Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles

Article abstract of DOI:10.1021/acs.nanolett.8b01912

Halide perovskites are known to support excitons at room temperatures with high quantum yield of luminescence that make them attractive for all-dielectric resonant nanophotonics and meta-optics. Here we report the observation of broadly tunable Fano resonances in halide perovskite nanoparticles originating from the coupling of excitons to the Mie resonances excited in the nanoparticles. Signatures of the photon-exciton ( hybrid ) Fano resonances are observed in dark-field spectra of isolated nanoparticles, and also in the extinction spectra of aperiodic lattices of such nanoparticles. In the latter case, chemical tunability of the exciton resonance allows reversible tuning of the Fano resonance across the 100 nm bandwidth in the visible frequency range, providing a novel approach to control optical properties of perovskite nanostructures. The proposed method of chemical tuning paves the way to an efficient control of emission properties of on-chip-integrated light-emitting nanoantennas.

Full text of DOI:10.1021/acs.nanolett.8b01912

Subscriber access provided by - Access paid by the | UCSB Libraries
Communication
Tunable Hybrid Fano Resonances in Halide Perovskite Nanoparticles
Ekaterina Tiguntseva, Denis G. Baranov, Anatoly Pushkarev, Battulga Munkhbat, Filipp E Komissarenko,
Marius Franckevicius, Anvar A. Zakhidov, Timur Shegai, Yuri S. Kivshar, and Sergey V. Makarov
Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.8b01912 • Publication Date (Web): 02 Aug 2018
Downloaded from http://pubs.acs.org on August 2, 2018
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
Tunable Hybrid Fano Resonances in Halide
Perovskite Nanoparticles
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Ekaterina Y. Tiguntseva,† Denis G. Baranov,∗,‡,† Anatoly P. Pushkarev,†
Battulga Munkhbat,‡ Filipp Komissarenko,† Marius Franckeviˇcius,¶ Anvar A.
Zakhidov,§,† Timur Shegai,‡ Yuri S. Kivshar,k,† and Sergey V. Makarov∗,†
†ITMO University, St. Petersburg 197101, Russia
‡Department of Physics, Chalmers University of Technology, 412 96 Gothenburg, Sweden
¶Center for Physical Sciences and Technology, LT-10257 Vilnius, Lithuania
§University of Texas at Dallas, Richardson TX 75080, USA
kNonlinear Physics Centre, Australian National University, Canberra ACT 2601, Australia
E-mail: denisb@chalmers.se; s.makarov@metalab.ifmo.ru
Abstract
Halide perovskites are known to support excitons at room temperatures with high
quantum yield of luminescence that make them attractive for all-dielectric resonant
nanophotonics and meta-optics. Here we report the observation of broadly tunable
Fano resonances in halide perovskite nanoparticles originating from the coupling of
excitons to the Mie resonances excited in the nanoparticles. Signatures of the photon-
exciton (’hybrid’) Fano resonances are observed in dark-field spectra of isolated nanopar-
ticles, and also in the extinction spectra of aperiodic lattices of such nanoparticles. In
the latter case, chemical tunability of the exciton resonance allows reversible tuning of
the Fano resonance across the 100 nm bandwidth in the visible frequency range, pro-
viding a novel approach to control optical properties of perovskite nanostructures. The
1
ACS Paragon Plus Environment

Nano Letters
Page 2 of 23
1
2
3
4
5
6
proposed method of chemical tuning paves the way to an efficient control of emission
properties of on-chip-integrated light-emitting nanoantennas.
7
8
9
Keywords
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Fano resonance, halide perovskites, excitons, nanophotonics, Mie resonances
Recently emerged novel platform for the study of light-matter interaction is associated
with the physics of halide perovskites, which are compounds of the form ABX3, where A
stands for organic (e.g., CH3NH3=MA) or inorganic (e.g., Cs) cations, B is usually lead
(Pb), and X is replaced by I, Br, or Cl.1 Halide perovskites represent a class of intriguing
dielectric materials with pronounced exciton resonances at room temperature, and high
quantum yield.2 Emission wavelengths of hybrid perovskites can be varied gradually over
the entire visible spectrum (400–800 nm) by replacing or mixing the anion compounds (I,
Br, or Cl) during the material synthesis process. These advantages, combined with low-
cost fabrication methods, allow for creating various perovskite-based active nanophotonic
structures and metadevices,3 such as metasurfaces,4,5 two-dimensional photonic crystals,6,7
nanoantennas,8 nanowaveguides and Fabry-Perot resonators,9 as well as whispering-gallery-
mode resonators.10
Coupling of an exciton to a resonant nanostructure may significantly alter the optical
response of the entire system. When a narrow exciton resonance of any material couples to
a broader cavity resonant mode, one can expect interference effects manifested in the char-
acteristic Fano lineshape in the spectrum.11–14 Such a hybrid Fano resonance is a ubiquitous
phenomenon encountered whenever a single resonance of a system interferes with either a
non-resonant background or another broader mode.15 Coherent coupling of an exciton with a
cavity mode has been observed in various configurations, involving organic molecules,11,16–19
semiconductors,20 carbon nanotubes,21 and transition metal dichalcogenides.22,23 However,
the Fano regime in an optically resonant perovskite nanostructure, which would enable novel
2
ACS Paragon Plus Environment

Page 3 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
opportunities owing to unique advantages of this class of materials, has not been explored.
Recent observation of perovskite nanoantennas exhibiting enhanced photoluminescence due
to intrinsic Mie resonances8 suggests that one can expect interference between exciton and
Mie resonance even in an isolated perovskite nanoparticle, as sketched in Fig. 1(a).
Here, we report on the first experimental observation of hybrid Fano resonances in isolated
perovskite nanoparticles and two-dimensional aperiodic structures of such nanoparticles. The
Fano resonances originate from a coupling of perovskite excitons to the geometry-driven Mie
resonances, and they are observed in the dark-field scattering and extinction spectra. The
unique material properties of the perovskite nanoparticles allow to tune chemically their
excitonic states over 100 nm frequency range in a reversible manner. Our findings may
have far reaching implications for a design of perovskite-based optoelectronic devices with
optimized optical characteristics as well as on-chip integrated reconfigurable light-emitting
nanoantennas.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Results and Discussion
Fano resonance in single perovskite nanoparticles. First, we inspect light scattering by a
single spherical perovskite nanoparticle in free space within the framework of Mie theory.25
Due to moderately high background refractive index of lead tribromide perovskites (e.g.,
MAPbBr3 or CsPbBr3), such nanoparticles exhibit prominent Mie resonances.8 Further-
more, since they possess pronounced exciton state with binding energy more than 70 meV26
(Fig. 1(b)), it is expected that coherent coupling of Mie modes of the particle to the excitons
of perovskite27 will result in a pronounced Fano resonance. To confirm this, we adopted
the permittivity of bulk MAPbBr3 from Ref. 24 and calculated spectra of scattering effi-
ciency, Qscat = σscat/πr2 of spherical nanoparticles versus particle radius r. The results
shown in Fig. 1(c) indeed exhibit an asymmetric behavior inherent for Fano resonance close
to the exciton resonance of perovskite at 520 nm correlated with the absorption peak. At
3
ACS Paragon Plus Environment

Nano Letters
Page 4 of 23
1
2
3
4
5
6
7
8
9
(a)
(b)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2.4
exciton
MAPbBr3
2.2
2.1
1.9
exciton
0.3
0.2
0.1
0
Mie mode
T=300 K
400
500
600
700
800 900 1000
Wavelength (nm)
(c)
(d)
Backward scattering (a.u.)
exciton
Scattering efficiency
200
180
160
140
120
100
80
200
180
160
140
120
100
80
max
MQ
ED
MD
exciton
0
400
500
600
700
800
400
500
Wavelength (nm)
600
700
800
Wavelength (nm)
Figure 1: Coupling of the exciton and Mie resonances in a perovskite nanopar-
ticle. (a) Schematic illustration of the coupling between the Mie resonance of a perovskite
nanoparticle and the exciton resonance of MAPbBr3 material. (b) Real and imaginary parts
of MAPbBr3 refractive index at room temperature adopted from Ref. 24. (c) Analytically
calculated scattering efficiency Qscat of a spherical MAPbBr3 nanoparticle in free space.
Overlaid lines depict approximate dispersion of the electric dipole, magnetic dipole, and
magnetic quadrupole resonances of the particle. The arrow indicates position of MAPbBr3
exciton. (d) Analytically calculated backward scattering for the same system. Overlaid lines
depict approximate dispersion of the first and second Kerker conditions, when intensity of
back scattered light is minimal or maximal, respectively.
4
ACS Paragon Plus Environment

Page 5 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
shorter wavelengths, the scattering efficiency is always suppressed: Mie resonances become
overdamped due to higher optical losses in perovskite above the bandgap energy.
Besides the dip in the scattering efficiency, the system exhibits another kind of asymmetric
dip in the backward scattering intensity, as depicted in Fig. 1(d). This dip corresponds to
the first Kerker condition,28 manifested as destructive interference between the electric and
magnetic dipoles in the backward direction, and it has a linear-like dispersion, as shown in
Fig. 1(d), in contrast to the Mie-exciton dip whose spectral position does not change with
nanoparticle radius.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In order to demonstrate experimentally the hybrid Mie-exciton Fano resonances in in-
dividual nanostructures, we fabricate MAPbBr3 nanoparticles by laser ablation29 of a per-
ovskite thin film (for details, see Methods). The resulting nanoparticles have spheroidal
shape and were dispersed with particle-to-particle distances of several microns, allowing to
measure the optical properties from individual particles (see Fig. 2(b)). The particles sizes
range mostly from 50 nm up to 400 nm, as revealed by scanning electron microscopy (SEM),
as shown in Fig. 2(d). Our optical measurements (see Methods for details) showed that
the spectral position of the photoluminescence (PL) peak from each nanoparticle does not
depend on the particle size, is centered at 539 nm, and has a line width of around 20 nm, as
shown in Fig. 2(a).
In Fig. 2(d), we present several experimental optical dark-field (DF) spectra collected
from single MAPbBr3 nanoparticles of different radius placed on a glass substrate as shown
in Fig. 2(c) (for details, see Methods). All spectra exhibit a clear dip at the exciton resonance
wavelength, which is the result of coherent coupling between the exciton and Mie resonances
of the spherical particles. To fit the spectra, we performed numerical simulations of light
scattering by a spherical MAPbBr3 nanoparticle on a glass substrate in COMSOL (for details,
see Methods). Fitting the DF spectra with the numerical results along with the corresponding
SEM images allow us to estimate the radii of the nanoparticles. Slight discrepancy between
experimental and numerically calculated spectra can be attributed to nonsphericity of the
5
ACS Paragon Plus Environment

Nano Letters
Page 6 of 23
1
2
3
4
5
6
7
8
9
(a)
(d)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
130 nm
135 nm
160 nm
165 nm
500
520
540
560
580
600
Wavelength (nm)
(b)
(с)
180nm
NA=0.42
S-pol
250
MAPbBr3
265 nm
GLASS
539
500
600
700
800
Wavelength (nm)
Figure 2: Coherent Mie-exciton coupling in single MAPbBr3 nanoparticles. (a)
PL spectra of a single MAPbBr3 nanoparticle. (b) The dark-field optical image (left) and
optical image of a single MAPbBr3 nanoparticle emitting light under cw UV excitation
(right). Scale bars in the photos are 1 µm. (c) Scheme of the dark-field optical spectroscopy
of single nanoparticles. (d) Measured dark-field spectra of MAPbBr3 nanoparticles (solid)
fitted with the simulated spectra (dashed). Inset: SEM images of MAPbBr3 nanoparticles
and their diameters. Scale bar in the SEM images is 200 nm.
6
ACS Paragon Plus Environment

Page 7 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
particles, as shown in Fig. 2(d). Nevertheless, despite the size and shape variations in our
experiments, the Fano dip always appears at the exciton wavelength for the particles with
diameters at least up to D ≈180 nm.
Tunable Fano resonances in nanoparticle structures. Although our measurements on
single nanoparticles essentially reveal Fano resonance features, achieving such regime in
large clusters of perovskite nanoparticles is much more attractive from the perspective of
optoelectronic30 and sensing applications.31 In addition, a possibility to tune the spectral
position of this resonance would be highly prospective for matching the Fano resonance with
various molecular transitions and optical resonances of other nanostructures.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In order to study the feasibility of the Fano resonance in macroscopic lattices of per-
ovskite nanoparticles and ways of its tunability, we fabricate a layer of randomly distributed
perovskite nanoparticles, see Fig. 3(a), with the same composition, where the organic cation
MA is replaced by an inorganic one (cesium, Cs), with similar excitonic, optical, and elec-
tronic properties.32 This composition (CsPbBr3) is more stable to environmental conditions
and to light-induced ions movement (segregation effect).33 On the other hand, MAPbBr3 in
more preferable for the laser ablation to create well-separated and large enough nanoparticles
supporting Mie resonances, but this material is not suitable for chemical tuning by the anion
exchange (see Secs. S5,S6 of Supporting information).
To produce aperiodic lattices of 80–600 nm halide perovskite nanoparticles (Fig. 3(a,b)),
the strategy of dispersion of the material in the polymer matrix (e.g. polyethylene oxide
(PEO), polyvinylpyrrolidone (PVP) or poly(9-vinylcarbazole) (PVK)) is adopted (for de-
tails, see Methods). Mixing 70 000 Mw PEO in DMF (10 mg/ml) and CsPbBr3 in DMSO
(137 mg/ml) solutions in 1:3 mass ratio affords the formation of a thin film containing
nanoparticles covered by a polymer layer (less than 50 nm, Ref. 30) after its spin-casting
and annealing at 110oC for 3 min. The choice of PEO is dictated by its ability to act as
a solid electrolyte facilitating the ionic transport and subsequent charge carriers injection
inside the luminescent layer in efficient pero-LEDs.30,34
7
ACS Paragon Plus Environment

Nano Letters
Page 8 of 23
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
HСl vapor
(b)
(a)
(c)
experimental
15
normal fit
10
5
doping process
Cl
H
H
Br
Cs
Cs
Cs
Br
Pb
Cl
Cl
Cl
1 mm
H
Br
Pb
Pb
H
0
100 150 200 250 300
Radius (nm)
(d) 2.4
2.3
1.0
(e)
0 sec
7 sec
0.8
0.6
0.4
0.2
0.0
18 sec
60 sec
152 sec
300 sec
2.2
2.1
2.0
1.9
1.8
1.7
300 400 500 600 700 800 900 1000
300 400 500 600 700 800 900 1000
Wavelength (nm)
Wavelength (nm)
Figure 3: Chemical doping of perovskite nanoparticles. (a) SEM image with a tilted
(45 degrees) view and (b) size distribution of chemically synthesized perovskite nanoparticles
(bars) with normal fit of this distribution (curve). (c) Schematic illustration of extinction
measurements: a cluster of perovskite nanoparticles of various radii placed on a glass sub-
strate is normally illuminated from top. Bottom: illustration of chemical doping of perovskite
particles. Br atoms in the atomic lattice of CsPbBr3 are being replaced with Cl under ex-
posure to dense vapor of hydrochloric acid. (d,e) Real and imaginary parts of refractive
indices of smooth CsPbBr3 films exposed to HCl vapor for various durations measured via
ellipsometry. The arrows indicate the direction of tuning.
8
ACS Paragon Plus Environment

Page 9 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
Tuning spectral position of the exciton is usually achieved via replacement of bromine (Br)
atoms with chlorine (Cl) atoms in the atomic lattice of CsPbBr3 during material synthesis.
However, this process is complicated by a very poor solubility of CsCl in organic solvents.
Therefore, we exploit a novel approach of chemical vapor anion exchange (CVAE) to form
mixed halide perovskites, which is schematically shown in Fig. 3(c). Complex refractive
indices of the perovskite films before and after CVAE process measured by ellipsometry are
presented in Fig. 3(d,e), revealing dramatic tuning of the exciton resonance position along
with significant modification of the refractive index in the entire spectral range.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
The intermediate phases of the aperiodic lattices of perovskite nanoparticles are obtained
via exposing CsPbBr3 samples to HCl vapor for 7, 18, 60, 152, and 300 s at 120oC (for details,
see Methods), yielding CsPbBr3−xClx (0 < x ≤ 3) nanoparticles that exhibit PL peaks at
503, 485, 466, 445, and 423 nm, respectively, see Fig. 4(a). To evaluate the reliability of the
obtained CsPbBr3−xClx (0 ≤ x ≤ 3) materials for the long term photonic applications, we
implement stability tests for continuous films. The samples are aged in the ambient air under
exposure to 80 mW cm−2 halogen lamp light. The films stability is monitored by measuring
the value of peak optical absorption at the exciton wavelength, which is changing over time.
Figure 4(b) shows a very slow decrease of this value by several percents upon aging the
perovskite films during 100 hours. Since higher chlorine content in the perovskite structure
increases the material band gap, the nanoparticles films with more chlorine content absorbed
less incident light from the halogen lamp and demonstrated reduced photobleaching rates in
comparison with that of PEO:CsPbBr3 film.
Experimentally measured extinction spectra (−logT) of the aperiodic lattices for differ-
ent doping concentrations shown in Fig. 4(c) exhibit pronounced asymmetric dips near the
exciton wavelengths, indicating that Fano resonance survives for extremely broad size dis-
tribution of nanoparticles. Expectedly, this feature of the extinction spectrum experiences
shift from 540 nm down to 420 nm upon increasing exposure of perovskite nanoparticles
to HCl. Since the PL emission wavelength (λPL) monotonically changes with concentration
9
ACS Paragon Plus Environment

Nano Letters
Page 10 of 23
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4: Chemical tuning of the Fano resonance in an aperiodic lattice of
nanoparticles. (a) Experimentally measured spectral positions of PL peak (blue squares),
Fano resonance (red triangles), and their bi-exponential fitting for a two-dimensional struc-
ture of perovskite nanoparticles chemically doped different time in HCl vapor. (b) Stability
of CsPbBr3−xClx thin films: peak absorption by the nanoparticles structures vs. time under
exposure to a halogen light source. (c) Measured extinction spectra of perovskite nanopar-
ticles with chemically tuned anion. Lorentzian-like curves around each spectrum show the
corresponding measured PL spectrum for each doping concentration. (d) Theoretically cal-
culated extinction spectra of a cluster of chemically tuned perovskite nanoparticles with the
size distribution from Fig. 3(b). The curves are shifted vertically for clarity.
10
ACS Paragon Plus Environment

Page 11 of 23
Nano Letters
1
2
3
4
5
6
7
8
of chlorine in the crystal lattice, the kinetics of the doping process is well described by a
bi-exponential law: λPL(t) = α1exp(−t/τ1) + α2exp(−t/τ2) + β.
We believe the fast exponent (τ1=10.94 s) specifies the chlorine doping of the initial tetrag-
9
onal phase of CsPbBr3 that is formed in the 88–130oC temperature range.35 In this case, the
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
˚
bromine substitution occurs easily because of the large lattice constants (a = b = 8.259A,
˚
c = 5.897A) and relatively low lattice energy. On the contrary, slow exponent (τ2=268.61
s) describes the further chemical modification of the cubic phase of formed CsPbBr3−xClx
˚
material possessing more dense lattice (a = b = c < 5.874A) with energy sufficient to resist
its structural transformation. The other fitting parameters are the following: α1 = 41.39 nm,
α2 = 89.86 nm, β = 394.2 nm.
The position of the Fano dip in the spectra, depending on duration of exposure to HCl
vapor, can be also described by the bi-exponential behavior with two exponents having short
τ1=9.82 s and long τ2=215.34 s time constants. The other fitting parameters for the Fano
dip are the following: α1=39.87 nm, α2=82.72 nm, β=393.7 nm.
In order to understand the origin of the Fano resonance in these spectra, we calculate
extinction by a lattice of perovskite nanoparticles with the use of an analytical model. Ex-
tinction of light propagating through a layer of particles with volume density N is caused by
absorption and diffuse scattering by the particles. The extinction coefficient of the medium
therefore is given by κ = 4πNσext with σext being the extinction cross section of the parti-
cles calculated with the Mie theory25 and the permittivities obtained from the ellipsometry
measurements shown in Fig. 4(d,e). Since reflection from a polymer film is negligible, trans-
mission through the film may be evaluated as T = e−κL with L being the film thickness.
To account for variation of the particles sizes, we calculated the averaged extinction cross
ꢀ
R
R
section σ¯ = f (R) σextdR
f (R) dR with f(R) being the statistical distribution of the
nanoparticles radii. According to the observed distribution of the nanoparticles sizes, see
Fig. 3(b), we assume the normal distribution of radii with the mean value of 160 nm and
standard deviation of 60 nm.
11
ACS Paragon Plus Environment

Nano Letters
Page 12 of 23
1
2
3
4
5
6
7
8
9
The resulting calculated extinction spectra (−logT) in Fig. 4(d) show reasonable agree-
ment with the experimental data in Fig.4(c), reproducing spectral positions of the Fano
dip. Discrepancy in the overall shape of the spectra may originate from the presence of the
glass substrate and non-sphericity of the particles, which shift Mie resonances. Nevertheless,
the modeling reveals the crucial contribution of the scattering part to the total extinction
spectra, resulting in appearance of a dip in extinction at the spectral position of the mate-
rial absorbance maximum (see comparison of absorption and scattering efficiencies of single
nanoparticles in Supporting information). The absorption maximum corresponding to the
exciton state gets ”hidden” into the Fano feature of the extinction spectrum. This result
is important for correct interpretation of experimentally measured transmittance spectra in
standard commercial spectrophotometers from very non-homogeneous perovskite films.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(a)
(b)
CsPbBr
CsPbBr
3
3
CsPbBr Cl
CsPbCl
3-x
x
3
↑HBr (60 s)
↑HCl (45 s)
↑HBr (45 s)
↑HCl (60 s)
350 400 450 500 550 600 650 700
350 400 450 500 550 600 650 700
Wavelength (nm)
Wavelength (nm)
Figure 5: Reversible chemical tuning of the Fano resonances. (a) Measured extinction
spectra of a lattice of perovskite nanoparticles with different compositions tuned via the
chemical vapor anion exchange method. Arrows indicate the tuning process in forward
direction by exposing the initial CsPbBr3 compound to HCl acid vapor for 300 seconds,
and in backward direction by exposing the resulting material to HBr vapor for the same
amount of time. (b) Similar extinction spectra for smaller exposure intervals, resulting in
intermediate compounds.
The presented technique of perovskite nanoparticles tuning via chemical doping is com-
12
ACS Paragon Plus Environment

Page 13 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
pletely reversible. Figure 5 demonstrates that after exposing clusters of CsPbBr3 nanopar-
ticles to HCl vapor for 300 s (for details, see Methods), and then for the same time to HBr
vapor, extinction spectrum returns exactly to its original state. This approach potentially
allows for multiple and precise tuning of resonant properties of a perovskite nanoparticle,
which might be integrated into some specific photonic circuit or nanophotonic design. Such
a direct in-place doping and broad spectral reconfiguration of light-emitting nanoantennas
cannot be achieved easily with the conventional semiconductor technologies, making tunable
halide perovskite indispensable in such kind of applications.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Finally, it is interesting to discuss the feasibility of reaching the strong light-matter
coupling regime between excitons and Mie resonances in a single perovskite nanoparticle.
With an increase of the coupling strength, coherent coupling of two resonances may switch to
the strong coupling regime, characterized by the presence of mixed exciton-polariton modes
in the system spectrum separated by the vacuum Rabi splitting.36–38 Exciton-polaritons
have recently been observed in micrometer-scale perovskite nanowires;39,40 however, Rabi
splitting was only detected in the dispersion of the waveguide mode, as opposed to splitting
of individual resonant modes. In our case, the strength of the coupling may be hindered by
the insufficient background refractive index of perovskites (≈ 2), which lowers the Q−factor
and increases the mode volume of the Mie modes. Potentially, alternative geometries, such
as a particle on a mirror, an oligomer, or a chain of nanoparticles, can provide a more
viable platform for realization of the strong coupling regime with a nanophotonic perovskite
structure.
Conclusion
We have observed a novel type of Fano resonance in isolated Mie-resonant halide perovskite
nanoparticles and also in disordered lattices of such nanoparticles. The Fano resonance has
been recorded as an asymmetric dip in the scattering spectra being originated from destruc-
13
ACS Paragon Plus Environment

Nano Letters
Page 14 of 23
1
2
3
4
5
6
7
8
9
tive interference between the exciton resonance and the Mie dipole mode of a nanoparticle.
Furthermore, the Fano resonances in disordered structures of CsPb(Br1−xClx)3 nanoparticles
have been tuned controllably over 100 nm in the visible frequency range by the chemical-
vapor-anion exchange. The proposed method of reversible tunability of the Fano resonances
can be useful for perovskite-based light-emitting nanoantennas integrated into a photonic
circuitry. Also, tunable Fano resonances can be employed for coloring or light outcoupling
in perovskite-based optoelectronic devices, especially for multilayer and multicolor architec-
tures for white-light emitting metadevices.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Methods
Fabrication of individual MAPbBr3 nanoparticles by laser ablation. For fabrication of nanopar-
ticles we use the laser printing method.29 In this approach, nanoparticles are fabricated from
a perovskite thin film in the forward-transfer geometry, when the receiving substrate is placed
under the film with a spacing of 50 µm. A solution of perovskite precursor (MAPbBr3)
is prepared in a N2-filled dry-box as follows: methylammonium bromide (MABr) in γ-
butyrolactone with dimethyl sulfoxide (GBL:DMSO) at the concentration of 1.5 M is used
to dissolve 1.5 M of lead bromine (PbBr2) in DMF. The solution is stirred and heated (70◦C)
overnight and used after filtration through 0.45 µm PTFE syringe filter. A perovskite layer
deposition is performed by a solvent-engineering technique inside the N2-filled dry-box, in-
cluding two step spin-coating process.41 At the first step, a solution precursor MAPbBr3 is
deposited at rotation speed 1000 rpm. The second step is the dripping 200 µl of the toluene
at 3000 rpm, which does not dissolve perovskite during the film formation. Each film is
annealed at 100◦C for 10 min.41 Glass substrates are washed by sonication in deionized wa-
ter, toluene, acetone, and isopropanol, consequently. Despite low cost and simplicity, this
method allows for the formation of high-quality films emitting light with high quantum yield
(up to 70 %).42 The perovskite nanoparticles are fabricated by employing Yb+3 femtosecond
14
ACS Paragon Plus Environment

Page 15 of 23
Nano Letters
1
2
3
4
5
6
7
8
9
laser pulses at λ = 1050 nm with energy around 50 nJ focused by 10× objective (NA=0.25).
According to our data, size of the nanoparticles was in the range of 50–500 nm, their shape
is quasi-spherical with some facets, whereas their position on a receiving substrate is random
(for details, see Supporting information and Ref. 8).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Optical properties of individual nanoparticles. We study optical resonances of the fabri-
cated perovskite nanoparticles deposited on a silica glass substrate, by using confocal dark-
field optical spectroscopy. The nanoparticles are excited at an oblique angle (65 degrees
with respect to the normal of the surface) by linearly polarized light from a halogen lamp
(HL-2000-FHSA) through a weakly-focusing objective (Mitutoyo M Plan Apo NIR, 10×,
NA = 0.28). Scattered light is collected from the top by an 50× objective (Mitutoyo M
Plan APO NIR, NA = 0.42), sent to Horiba LabRam HR spectrometer and projected onto
a thermoelectrically cooled charge-coupled device (CCD, Andor DU 420A-OE 325) with a
150-g/mm diffraction grating.
Fabrication of clusters of CsPbBr3 perovskite nanoparticles. Lead(II) bromide (99.999%),
cesium bromide (99.999%) and N,N-dimethylformamide (DMF, anhydrous, 99.8%) are pur-
chased from Sigma-Aldrich. Dimethyl sulfoxide (DMSO, anhydrous, 99.8%) and poly(ethylene
oxide) (average Mw 70 000) are purchased from Alfa Aesar and Agilent, respectively. All
materials are used as received.
Perovskite solution is prepared by dissolving PbBr2 (73.4 mg, 0.2 mmol) and CsBr
(63.6 mg, 0.3 mmol) in 2 ml of DMSO. An excess of cesium bromide is taken to fully
convert lead bromide into the perovskite. The solution is stirred for 1 h without heating.
o
PEO (30 mg) is dissolved in 3 ml of DMF by stirring overnight at 70 C. 170 mg of the
perovskite solution is mixed with 510 mg of the PEO solution to give perovskite-polymer
o
ink. The ink is stirred at 120 C for 30 min and then filtered by using 0.45 µm syringe fil-
ter with PTFE membrane. Fused silica substrates are cleaned subsequently with detergent
water, acetone, and isopropanol for 5 min with sonication, then treated with oxygen plasma
at 100 W power for 3 min. The organic-inorganic composite films are spin-casted onto the
15
ACS Paragon Plus Environment

Nano Letters
Page 16 of 23
1
2
3
4
5
6
7
8
o
substrates at 1500 rpm for 1 min and further annealed at 110 C for 3 min on a hotplate.
Solution preparation and film deposition are carried out inside N2 filled glovebox with both
O2 and H2O level not exceeding 1 ppm.
9
Chemical vapor anion exchange method. Doping of the CsPbBr3:PEO films by chlorine
is conducted outside the glovebox at ≈30% humidity. The sample is placed in a glass Petri
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
o
dish bottom and preheated on the hotplate at 120 C for 2 min before the treatment. A
glass low form weighing bottle (40×25 mm, 25 ml) is preheated in an oven at 120 oC as well.
Then 3 mg of HCl azeotrope (37%, Vecton) onto a glass substrate is put near the sample,
and all the system is encapsulated by the hot glass weighing bottle. After specific lapse of
time the system is dismantled and the sample is heated up to 200oC at 40oC deg/min rate
to eliminate possible structural defects of the crystal lattice. To confirm the reversibility of
the anion exchange in the perovskite crystal lattice CsPbCl3:PEO film obtained is treated
in a similar manner by 3 mg of HBr azeotrope (40%, Vecton). All the samples are cooled
down to room temperature before the measurements.
Optical degradation measurements. Optical degradation studies of perovskite films were
undertaken while measuring integrated absorption of the samples at different times with
AvaSpec-HS1024x58/122 fiber optic spectrometer (Avantes). For photodegradation studies,
samples were continuously illuminated with halogen lamp which was collimated and focused
on sample producing power density of about 80 mW cm−2.
Ellipsometry. Ellipsometry measurements were carried out in air using J.A. Woollam
M2000 ellipsometer over the wavelength range of 245–1000 nm with a step of 1 nm. Inci-
dence angles from 65o to 75o relative to the surface normal were scanned with a step of 5o for
reflection ellipsometry. The analysis of ellipsometric data was performed using the software
WVASE-32 (J.A. Woolam Co.). Thicknesses of perovskite films on silicon substrates were
determined by P-7 Stylus Profiler (KLA Tencor). Using the obtained perovskite film thick-
ness, the optical constants (refractive index n and extinction coefficient k) were extracted
from the ellipsometric data using the point-by-point method.
16
ACS Paragon Plus Environment

Page 17 of 23
Nano Letters
1
2
3
4
5
6
7
8
Shape and size characterization. The fabricated nanoparticles are visualized and in-
spected using a field-emission scanning electron microscopy (SEM, JEOL, Cross Beam 1540
XB).
9
Optical characterization of lattices of perovskite nanoparticles. All samples with nanopar-
ticles clusters are visualized in an optical microscope (Axio Imager.A2m, Carl Zeiss) with
different objectives (×10, ×20, ×50) under illumination by a halogen light source (HAL 300)
in reflection mode and by 365-nm line of a mercury lamp (HBO 100) in a luminescent mode
(see images in Supporting information). Extinction spectra are measured in a UV-VIS-NIR
spectrophotometer (Shimadzu UV-2600).
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Numerical simulations of dark field scattering. Simulations are performed with the use of
commercial software COMSOL. Permittivity of bulk MAPbBr3 is adapted from Ref. 24. Par-
ticles are placed on a glass substrate and illuminated by an s-polarized total field/scattered
field source incident at an angle of 65 degrees. Scattered light is collected by a power monitor
with NA≈ 0.4 corresponding to the objective used in the experiment.
Authors information
Corresponding Authors
*E-mail (D.G.B.): denisb@chalmers.se; *E-mail (S.V.M.): s.makarov@metalab.ifmo.ru.
Notes
The authors declare no competing financial interests.
Supporting Information Available
Information on size distribution of nanoparticles, multipole decomposition of electromag-
netic field for spherical nanoparticles, scattering and absorption efficiencies, information on
17
ACS Paragon Plus Environment

Nano Letters
Page 18 of 23
1
2
3
4
5
6
chemical tuning of MAPbBr3 nanoparticles, laser fabrication of CsPbBr3 nanoparticles, and
morphology characterization of MAPbBr3 and CsPbBr3 films used for laser ablation.
7
8
9
Acknowledgement
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
This work was supported by the Ministry of Education and Science of the Russian Federation
(project 16.8939.2017/8.9, for the sample preparation) and the Russian Science Foundation
(project 17-73-20336, for the optical characterization). D.G.B. and T.S. acknowledge a
support from the Knut and Alice Wallenberg Foundation. M.F. acknowledges a funding from
the European Social Fund according to the activity ‘Improvement of researchers’ qualification
by implementing world-class R&D projects of Measure No. 09.3.3-LMT-K-712-01-0031. Y.K.
acknowledges a support from the Strategic Fund of the Australian National University. A.Z.
acknowledges a partial support from the Welch Foundation (grant AT 16-17).
References
(1) Sutherland, B. R.; Sargent, E. H. Nature Photonics 2016, 10, 295–302.
(2) Sutter-Fella, C. M.; Li, Y.; Amani, M.; Ager III, J. W.; Toma, F. M.; Yablonovitch, E.;
Sharp, I. D.; Javey, A. Nano Letters 2015, 16, 800–806.
(3) Makarov, S.; Furasova, A.; Tiguntseva, E.; Hemmetter, A.; Berestennikov, A.;
Pushkarev, A.; Zakhidov, A.; Kivshar, Y. arXiv preprint arXiv:1806.08917 2018,
(4) Makarov, S. V.; Milichko, V.; Ushakova, E. V.; Omelyanovich, M.; Cerdan Pasaran, A.;
Haroldson, R.; Balachandran, B.; Wang, H.; Hu, W.; Kivshar, Y. S.; Zakhidov, A. A.
ACS Photonics 2017, 4, 728–735.
(5) Gholipour, B.; Adamo, G.; Cortecchia, D.; Krishnamoorthy, H. N.; Birowosuto, M.;
Zheludev, N. I.; Soci, C. Advanced Materials 2017, 29, 1604268.
18
ACS Paragon Plus Environment

Page 19 of 23
Nano Letters
1
2
3
4
(6) Chen, S.; Roh, K.; Lee, J.; Chong, W. K.; Lu, Y.; Mathews, N.; Sum, T. C.; Nur-
5
6
mikko, A. ACS Nano 2016, 10, 3959–3967.
7
8
9
(7) Gharajeh, A.; Haroldson, R.; Li, Z.; Moon, J.; Balachandran, B.; Hu, W.; Zakhidov, A.;
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Gu, Q. Optics Letters 2018, 43, 611–614.
(8) Tiguntseva, E.; Zograf, G. P.; Komissarenko, F. E.; Zuev, D. A.; Zakhidov, A. A.;
Makarov, S. V.; Kivshar, Y. S. Nano Letters 2018, 18, 1185–1190.
(9) Zhu, H.; Fu, Y.; Meng, F.; Wu, X.; Gong, Z.; Ding, Q.; Gustafsson, M. V.; Trinh, M. T.;
Jin, S.; Zhu, X. Nature Materials 2015, 14, 636.
(10) Tang, B.; Dong, H.; Sun, L.; Zheng, W.; Wang, Q.; Sun, F.; Jiang, X.; Pan, A.;
Zhang, L. ACS Nano 2017, 11, 10681.
(11) Wiederrecht, G. P.; Wurtz, G. A.; Hranisavljevic, J. Nano Letters 2004, 4, 2121.
(12) Govorov, A. O.; Bryant, G. W.; Zhang, W.; Skeini, T.; Lee, J.; Kotov, N. A.;
Slocik, J. M.; Naik, R. R. Nano Letters 2006, 6, 984–994.
(13) Adato, R.; Artar, A.; Erramilli, S.; Altug, H. Nano Letters 2013, 13, 2584–2591.
(14) Chen, X.-W.; Sandoghdar, V.; Agio, M. Physical Review Letters 2013, 110, 153605.
(15) Limonov, M. F.; Rybin, M. V.; Poddubny, A. N.; Kivshar, Y. S. Nature Photonics
2017, 11, 543–554.
(16) Liu, G. L.; Long, Y.-T.; Choi, Y.; Kang, T.; Lee, L. P. Nature Methods 2007, 4, 1015.
(17) Ni, W.; Yang, Z.; Chen, H.; Li, L.; Wang, J. Journal of the American Chemical Society
2008, 130, 6692–6693.
(18) Ni, W.; Ambjornsson, T.; Apell, S. P.; Chen, H.; Wang, J. Nano Letters 2010, 10, 77.
19
ACS Paragon Plus Environment

Nano Letters
Page 20 of 23
1
2
3
4
5
6
7
8
(19) Zhang, Y.; Meng, Q.-S.; Zhang, L.; Luo, Y.; Yu, Y.-J.; Yang, B.; Zhang, Y.; Esteban, R.;
Aizpurua, J.; Luo, Y.; Yang, J.-L.; Dong, Z.-C.; Hou, J. Nature Communications 2017,
8, 15225.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(20) Achermann, M. The Journal of Physical Chemistry Letters 2010, 1, 2837–2843.
(21) Falk, A. L.; Chiu, K.-C.; Farmer, D. B.; Cao, Q.; Tersoff, J.; Lee, Y.-H.; Avouris, P.;
Han, S.-J. Physical Review Letters 2017, 118, 257401.
(22) Kern, J.; Tru¨gler, A.; Niehues, I.; Ewering, J.; Schmidt, R.; Schneider, R.; Najmaei, S.;
George, A.; Zhang, J.; Lou, J.; Hohenester, U.; Michaelis De Vasconcellos, S.; Brats-
chitsch, R. ACS Photonics 2015, 2, 1260–1265.
(23) Abid, I.; Bohloul, A.; Najmaei, S.; Avendano, C.; Liu, H.-L.; Pechou, R.; Mlayah, A.;
Lou, J. Nanoscale 2016, 8, 8151–8159.
(24) Brittman, S.; Garnett, E. C. Journal of Physical Chemistry C 2015, 120, 616–620.
(25) Bohren, C. F.; Huffman, D. R. Absorption and Scattering of Light by Small Particles;
John Wiley & Sons, 2008.
(26) Tanaka, K.; Takahashi, T.; Ban, T.; Kondo, T.; Uchida, K.; Miura, N. Solid State
Communications 2003, 127, 619–623.
(27) Platts, C.; Kaliteevski, M.; Brand, S.; Abram, R.; Iorsh, I.; Kavokin, A. Physical Review
B 2009, 79, 245322.
(28) Kerker, M.; Wang, D.-S.; Giles, C. JOSA 1983, 73, 765–767.
(29) Dmitriev, P.; Makarov, S.; Milichko, V.; Mukhin, I.; Gudovskikh, A.; Sitnikova, A.;
Samusev, A.; Krasnok, A.; Belov, P. Nanoscale 2016, 8, 5043–5048.
(30) Bade, S. G. R.; Li, J.; Shan, X.; Ling, Y.; Tian, Y.; Dilbeck, T.; Besara, T.; Geske, T.;
Gao, H.; Ma, B. ACS Nano 2015, 10, 1795–1801.
20
ACS Paragon Plus Environment

Page 21 of 23
Nano Letters
1
2
3
4
(31) Wu, C.; Khanikaev, A. B.; Adato, R.; Arju, N.; Yanik, A. A.; Altug, H.; Shvets, G.
5
6
Nature Materials 2012, 11, 69.
7
8
9
(32) Kulbak, M.; Cahen, D.; Hodes, G. Journal of Physical Chemistry Letters 2015, 6,
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2452–2456.
(33) Sutton, R. J.; Eperon, G. E.; Miranda, L.; Parrott, E. S.; Kamino, B. A.; Patel, J. B.;
Horantner, M. T.; Johnston, M. B.; Haghighirad, A. A.; Moore, D. T. Advanced Energy
Materials 2016, 6, 1502458.
(34) Chen, P.; Xiong, Z.; Wu, X.; Shao, M.; Ma, X.; Xiong, Z.-h.; Gao, C. The Journal of
Physical Chemistry Letters 2017, 8, 1810–1818.
(35) Hirotsu, S.; Harada, J.; Iizumi, M.; Gesi, K. Journal of the Physical Society of Japan
1974, 37, 1393–1398.
(36) Khitrova, G.; Gibbs, H. M.; Kira, M.; Koch, S. W.; Scherer, a. Nature Physics 2006,
2, 81–90.
(37) T¨orma¨, P.; Barnes, W. L. Rep. Prog. Phys 2015, 78, 013901.
(38) Baranov, D. G.; Wersa¨ll, M.; Cuadra, J.; Antosiewicz, T. J.; Shegai, T. ACS Photonics
2018, 5, 24.
(39) Du, W.; Zhang, S.; Shi, J.; Chen, J.; Wu, Z.; Mi, Y.; Liu, Z.; Li, Y.; Sui, X.; Wang, R.;
Qiu, X.; Wu, T.; Xiao, Y.; Zhang, Q.; Liu, X. ACS Photonics 2018, 5, 2051–2059.
(40) Evans, T. J.; Schlaus, A.; Fu, Y.; Zhong, X.; Atallah, T. L.; Spencer, M. S.; Brus, L. E.;
Jin, S.; Zhu, X.-Y. Advanced Optical Materials 2018, 6.
(41) Jeon, N. J.; Noh, J. H.; Kim, Y. C.; Yang, W. S.; Ryu, S.; Seok, S. I. Nature Materials
2014, 13, 897–903.
21
ACS Paragon Plus Environment

Nano Letters
Page 22 of 23
1
2
3
4
5
6
7
8
(42) Deschler, F.; Price, M.; Pathak, S.; Klintberg, L. E.; Jarausch, D.-D.; Higler, R.; Hut-
tner, S.; Leijtens, T.; Stranks, S. D.; Snaith, H. J. Journal of Physical Chemistry Letters
2014, 5, 1421–1426.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
22
ACS Paragon Plus Environment

Page 23 of 23
Nano Letters
1
2
3
4
Graphical TOC Entry
5
6
7
Chemical doping
Tuning
8
9
Cs
Cs
Cs
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Cl
Cs
Cs
Cl
Pb
Br
Br
Cl
BrH
exciton
-
+
Cs
Cl
H
Cs
Mie mode
H
Cl
23
ACS Paragon Plus Environment