Synthesis and optical properties of yttria-doped ZrO2 nanopowders

Article abstract of DOI:10.1016/j.jallcom.2007.04.011

Yttria-doped zirconia (YDZ) nanopowders were synthesized via a solvothermal route using ethanol as solvent. Evolution of crystal phases for different amount of yttria-doped samples were studied by X-ray diffraction (XRD). Morphology and component of the as-synthesized cubic YDZ were characterized by scanning electron microscopy (SEM) and energy dispersion spectrum (EDS). Defects of the sample were detected using ultraviolet-vis (UV-vis) absorption spectrum and photoluminescence (PL) spectrum. The results indicated that cubic structured nanocrystals can be obtained through doping 4 mol% Y₂O₃ into ZrO₂ lattice. The particles had sphere morphology with an average crystal size of 10 nm and agglomerated into bigger spheres with a diameter of about 120 nm. Mechanism of the agglomeration was also discussed. UV spectra showed two absorption peaks, red shift for both of the adsorption edges was observed. PL spectra with excitation wavelength of 260 and 420 nm revealed six fluorescence peaks which were regarded as various energy levels in the band gap and as the evidence of existence of oxygen vacancies in the as-synthesized sample.

Full text of DOI:10.1016/j.jallcom.2007.04.011

Journal of Alloys and Compounds 458 (2008) 474–478
Synthesis and optical properties of yttria-doped ZrO2 nanopowders
Huaming Yang∗, Jing Ouyang, Xiaolong Zhang,
Ning Wang, Chunfang Du
Department of Inorganic Materials, School of Resources Processing and Bioengineering,
Central South University, Changsha 410083, China
Received 27 February 2007; received in revised form 31 March 2007; accepted 2 April 2007
Available online 6 April 2007
Abstract
Yttria-doped zirconia (YDZ) nanopowders were synthesized via a solvothermal route using ethanol as solvent. Evolution of crystal phases
for different amount of yttria-doped samples were studied by X-ray diffraction (XRD). Morphology and component of the as-synthesized cubic
YDZ were characterized by scanning electron microscopy (SEM) and energy dispersion spectrum (EDS). Defects of the sample were detected
using ultraviolet–vis (UV–vis) absorption spectrum and photoluminescence (PL) spectrum. The results indicated that cubic structured nanocrystals
can be obtained through doping 4 mol% Y2O3 into ZrO2 lattice. The particles had sphere morphology with an average crystal size of 10 nm and
agglomerated into bigger spheres with a diameter of about 120 nm. Mechanism of the agglomeration was also discussed. UV spectra showed two
absorption peaks, red shift for both of the adsorption edges was observed. PL spectra with excitation wavelength of 260 and 420 nm revealed six
fluorescence peaks which were regarded as various energy levels in the band gap and as the evidence of existence of oxygen vacancies in the
as-synthesized sample.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Nanostructured materials; Chemical synthesis; Optical properties; X-ray diffraction
1. Introduction
expansion of about 3–5% in volume [10–12], which will cause
the cracking of ceramics and will handicap the large scale usage
of ZrO2 unless it has been stabilized. Previous studies were
focused on zirconia stabilization by different kinds of addi-
tives, such cations with lower valence than Zr4+ as Al3+, Y3+,
Ca2+, even oxides such as CeO2, SiO2, TiO2 whose cations have
the same valence with that of the hostage have been introduced
into the lattice of ZrO2 to form heat standing materials [13–18].
Among these additives, yttria (Y2O3) was an effective stabilizer
and was most widely used. When quantitative lower valence
doping cations (i.e., Y3+) were introduced into the ZrO2 lattice,
they would substitute the position of Zr4+ and would induce
the mobile oxygen vacancies’ creation in the oxygen sub-lattice
for the sake of keeping electrical neutrality [19]. The vacancies,
which distributed evenly around the zirconium atoms, would
decrease the repulsion force of O–O bond and merge the volume
expansion or shrinkage during fluctuation of temperature.
In recent years, nanosized zirconia materials have attracted
much attentions, ZrO2 nanomaterials with different grain diame-
ters and various surface topography have been obtained through
many methods such as spray pyrolysis, nonhydrolytic sol–gel,
hydrothermal synthesis, template method, co-precipitation and
Zirconia (ZrO2) is a kind of functional materials with many
unique properties. It is the only transitional metal oxide that
presents both acidity and alkalescence centers, along with the
high performance in mechanical, thermal, optical, catalytic
properties and high ionic conductivity at elevated temperatures
(>1000 K) [1–4], so, ZrO2 has been widely used in the fields
of functional ceramics as well as electronic materials, oxygen
sensors, humidity sensors, anode in fuel cells and catalytic mem-
brane reactors [5–9].
It is well established that zirconia has three crystal struc-
tures and will undergo transformation along with the following
avenue:
◦
◦
◦
monoclinc1←170→Ctetragonal2←370→Ccubic2←715→Cliquid
Martensitic transformation will occur when zirconia changes
from tetragonal to monoclinic structure, along with lattice
∗
Corresponding author. Tel.: +86 731 8830 549; fax: +86 731 8710 804.
E-mail address: hmyang@mail.csu.edu.cn (H. Yang).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2007.04.011

H. Yang et al. / Journal of Alloys and Compounds 458 (2008) 474–478
475
so on [20–24]. But there exist many shortcomings for those
methods, including subsequent heat treatment at high tem-
peratures required, easily reuniting at room temperature, poor
dispersibility, non-uniform grain diameter distribution, low spe-
cific surface area and activity, etc. In addition, the solvothermal
route has not been intensively studied for the synthesis of ZrO2
nanomaterials, countering on the superiority of this method such
as easily controlling the grain size, particle morphology, crys-
talline phase and surface chemistry by simply regulating sol
composition, reaction temperature, solvent property, additives
and aging time [25].
Recently, more and more attentions were attracted to the
potential application of ZrO2 as host for telecommunication
amplifiersandrepeatersaswellascathoderadiationtubes, which
were originated from the much lower phonon energy of ZrO2
than that of SiO2 host, because the stretching frequency of sil-
ica matrix is ∼1100 cm−1 and that of zirconia matrix is only
∼470 cm−1. Thus, higher efficiency of luminescence yielding
could be expected from zirconia matrix, because the lower the
phonon energy of the host matrix, the lower probability of non-
radiative relaxation, and the higher the quantum yielding of
luminescence [26]. Therefore, to study the optical properties
of ZrO2 nanomaterials is of great interest. Although the detailed
PL mechanism for the bulk YDZ and high temperature aged
YDZ particles has been intensively studied [27–29], and PL
spectra have been detected for pure ZrO2 nanopowders, which
illustrated three emission peaks under excitation of high energy
UV light (λ = 212 nm), and a red colored emission light cen-
tered at 602 nm was observed under lower energy violet light
excitation (λ = 412 nm) [30]. To the best of our knowledge, the
optical properties (including UV–vis and PL) of YDZ nano-
materials and their mechanisms are still keeping in obscure. In
present work, the solvothermal synthetic method was adopted in
the synthesizing of YDZ nanoparticles. Evaluation of the crys-
talline phase for different amount of yttria-doped samples and
morphology of the sample were studied. Optical properties of
the nano-scaled YDZ materials have been studied and possible
mechanisms for these phenomena were discussed.
Sirion200 field emission scanning electron microscopy (SEM) equipped with
Oxford EDAX energy dispersion spectrum (EDS) analyzer. Ultraviolet visible
(UV–vis) absorption spectrum of the powder was carried out on Shimadzu UV-
2450 spectrometer. Room temperature photoluminescence (RTPL) spectrum of
the sample was detected on a Hitachi H-2500 fluorescence spectrometer using
a Xe lamp as the light source.
3. Results and discussion
Fig. 1a shows the XRD patterns of YDZ nanocrystals synthe-
sized in ethanol at 180 ◦C with different quantity of Y2O3 dopant
in the zirconia. As it is difficult to distinguish between tetragonal
and cubic phase from the XRD patterns due to the XRD peaks
resemblance of the two phases and to peak broadening resulted
from the nanocrystal size effect, all of the relevant diffraction
peaks were indexed according to the cubic symmetry. As can
be seen from Fig. 1 that only monoclinic ZrO2 (JCPDS No. 65-
1024) existed in the resulted product when no yttria was added
(curve Fig. 1a), but both cubic and monoclinic ZrO2 existed
when 2.5 mol% of Y2O3 was introduced into the zirconia lattice
(curve Fig. 1b). Pure cubic phase ZrO2 (JCPDS No. 49-1642,
a = 0.5128 nm) was observed on XRD curve of 4 mol% Y2O3
doped ZrO2 which is shown in Fig. 1c, suggesting that 4 mol%
quantity of Y2O3 can reach cubic structured ZrO2 nanocrystals
in our experimental conditions. As regards, the latter charac-
terizations were all applied to the 4 mol% Y2O3 doped ZrO2
sample (4YDZ as the abbreviation here after). The calculated
crystal size of the resulted sample shown in Fig. 1c is 9.5 nm
according to Sherrer’s equation based on full width at half max-
imum (FWHM) of c-ZrO2 (1 1 1) facts. Lattice parameter of
the cubical indexed yttria stabilized zirconia is 0.5141 nm, a bit
larger than the reference, which may be attributed to the yttrium
dopant entering the zirconia lattice.
Although it has been established that 6–8 mol% of Y2O3 were
required to fully stabilize cubic ZrO2 crystals [31], the ab-initio
calculation plus transmission electron microscopy (TEM) inves-
tigation revealed that c-ZrO2 can even keep stable when size of
the nanocrystals was less than 2 nm [32]. Another report sug-
gested that t-ZrO2 were stable for crystal size between 15 nm
2. Experimental
2.1. Material synthesis
Thestartingmaterialsincludezirconylchlorideoctahydrate(ZrOCl2·8H2O),
yttrium nitrate (Y(NO3)3), and ethanol (CH3CH2OH). All reagents were analyt-
ical grade and used without further purification. In a typical synthesis process,
1 mmol of raw sources followed the composition of (Y2O3)x(ZrO2)100−x (x = 0,
1, 2.5, 4) were disolved into 200 mL de-ionized water and precipitated by
0.1 mol L−1 ammonia until pH of the system turned to 7, then the gel were
centrifuged and treated in hermetically closed autoclaves in ethanol circum-
stance at 180 ◦C for 16 h. The products were washed with ethanol and then dried
at 60 ◦C in air.
2.2. Characterization
Crystalline phase evolution of the resulted powder was detected by X-ray
diffraction (XRD) analysis with a RIGAKU D/max-2550VB+ 18 kW powder
˚
diffractometer with Cu K␣-radiation (λ = 1.541806A), data were collected from
10◦ to 90◦ of 2θ with a step width of 0.02◦. The particles suspension was dropped
on an aluminum stub for morphology and composition characterization by FEI
Fig. 1. XRD curves for samples of (a) pure ZrO2, (b) 2.5 mol% Y2O3 and (c)
4 mol% Y2O3 doped ZrO2 via solvothermal process.

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H. Yang et al. / Journal of Alloys and Compounds 458 (2008) 474–478
and 60 nm [26]. The crystal size of our sample revealed to be
9.5 nm, so, it is not surprising that our sample reached the pure
cubic structured ZrO2 by doping only 4% of the yttrium oxide.
In aqua ZrOCl2 solvent, the tetrameric ion
8+
(Zr(OH)2·4H2O)4
is the major species, the four zirco-
nium atoms in each unit are arranged in a square, and each
of them is coordinated by four bridging –OH groups and four
H2O molecules [33,34]. In alkali circumstance (i.e., NH4OH
was dropped into the solution), the tetrametric ions would
release H+ ions from the coordinated water and consequently
add some nondridging –OH groups onto the zirconium atoms
(8−4x)+
to produce the (Zr(OH)2+x·(4 − x)H2O)4
groups. After
certain dosage of OH− ions was dropped into the solution,
pH of the mixture would turn to be neutral, which is the
destination of our titration, and the (Zry(OH)2+x−2y·zH2O)n
groups would come into being. In solvothermal conditions, the
(Zry(OH)2+x−2y·zH2O)n groups should dehydrate to form ZrO2.
As a result, the process for ZrO2 and Y2O3 formation in our
experimental conditions should be illustrated as the following:
8+
(Zr(OH)2·4H2O)4
↔ (Zr(OH)2+x·(4 − x)H2O)4(8−4x)+ + 4xH+
(1)
(2)
(8−4x)+
(Zr(OH)2+x·(4 − x)H2O)4
↔ (Zry(OH)2+x−2y·zH2O)n↓ + mH2O
(Zry(OH)2+x−2y·zH2O)n = nyZrO2 + lH2O
Y(NO3)3 + 3NH4OH = Y(OH)3↓ + 3NH4NO3
2Y(OH)3 = Y2O3 + 3H2O
(3)
(4)
(5)
Fig. 2. (a) SEM image of 4YDZ sample, tiny white particles are ZrO2 nanocrys-
tals, sphere particles are agglomerates, and holes are spaces between each
agglomerates; (b) EDS spectrum of the selected area, the inset is the element
integration value, where carbon (C) are not included in the table according to
the original experiment.
Fig. 2a shows the SEM image of 4YDZ sample. The size
of white particles was observed to be about 10 nm in diameter
which is perfectly accepted with that calculated from XRD data.
Moderate aggregation of the nanoparticles, however, seems to
be present in this sample. Sizes of the conglomeration are about
120 nm according to the SEM images. EDS spectrum of the
4YDZ sample was shown in Fig. 2b, indicating that the sam-
ples are consisted of O, Y and Zr elements, where C should be
attributed to the adsorbed organic solvent and Al peak existence
is caused by the supporting stub of the SEM sample, no peaks
belonged to other impurities appeared on the spectrum. Accord-
ing to the element integrating data shown in the inserted table,
the atomic content (3.64%) of Y is larger than that from the
experiment date (1.81%). This may be caused by the deviation
of the instrument detection, as zirconium adheres to yttrium in
the Periodic Table and their electron shells are similar, it was
rather difficult for the detector to distinguish the differences of
energy between X-ray yielded from Y atoms and that from Zr
atoms.
eration of ZrO2 nanoparticles in gel as effective as possible is
of great importance in preparing ZrO2 nanomaterials, especially
when the nanoparticles should further be used as the building
blocks of functional materials. The DLVO theory [35] has dom-
inated interpretation of aggregating behavior of micro-particles
in colloid and interface circumstance. According to the famous
theory, there exists an energy barrier (V) for agglomeration of the
particles in colloid, where V is determined by many physical and
chemical properties of the constituents of the colloid. It has been
illustrated by Hua et al. [34] that, in solvothermal conditions, the
dielectric constant (ε) of the media solvent and surface poten-
tial (ϕ) of the ZrO2 surface take the most responsibility for the
agglomeration behavior of these particles. In solvent with high ε
value, the as-prepared nanoparticles tend to form the irregularly
shaped hard aggregates, rather than sphere soft agglomerates.
Solvent with relatively lower ε will decrease the energy barrier
for particles’ agglomeration and will produce the sample consist
of soft agglomerates. Furthermore, surface groups will take the
dominant effect on stabilizing the nanoparticles and on forming
the soft agglomerates, rather than hard aggregates. As can be
summarized in Fig. 3 that, ZrO2 nanoparticles initialize from
Meanwhile, ZrO2 is easy to form sphere aggregates in most
cases, such as the ZrO2 micro spheres with diameter of 0.8–2 ␮m
synthesized by hydrolysis of zirconium tetraalkoxide [7] and
the spherical hard-aggregations with an average diameter up to
3 ␮m prepared by solvothermal route in the mingled solvent of
methanol and acetone [34]. Therefore, to prevent the conglom-

H. Yang et al. / Journal of Alloys and Compounds 458 (2008) 474–478
477
Fig. 3. Schematical summarizing for aggregate behavior of ZrO2 in ethanol thermal treating.
(Zry(OH)2+x−2y·zH2O)n colloid under solvothermal treatment
(step I in Fig. 3), then the particles tend to form soft agglomerates
in submicro scale (step II).
through linearly fitting the corresponding plots at the biggest
slope of wavelength against adsorption coefficient (␣) spectrum
and then extrapolating the fitting line to ␣ = 0 to derive the band
gap (Eg) [39]. The fitting lines for both of the absorption peaks
were also shown in Fig. 4, the edges observed were 4.83 eV for
the stronger absorption and 3.44 eV for the weaker one. Com-
pared with microwave synthesized ZrO2 nanoparticles [30], for
which an absorption onset of about 3.5 eV and a peak at about
4.25 eV were observed, and with the bulk YDZ, about 5.2 eV
according to Ref. [21] and 5.0–5.5 eV according to Ref. [28],
our results indicated a red shift of the absorption edge for the
as-prepared 4YDZ sample.
The room temperature photoluminescence (RTPL) spectra of
the 4YDZ nanoparticles obtained at two different excitations are
shown in Fig. 5. It was suggested that the emissions appear at
short wavelength excitation should be ascribed to the near band-
edge transitions [20,40], so, light beam with energy similar to
the absorption edge of the high level direct band transition was
chosen as the excitation energy (Fig. 5a). Under this condition,
five fluorescence emission bands centered at 356 nm, 396 nm,
412 nm, 450 nm and 468 nm were observed respectively, sug-
gesting that the excited electrons transfer to at least five lower
energy levels through vibration or because of energy splitting,
andthenradiativerelaxationoccurandyieldphotonswithenergy
equal to the gap between bottom of the excited levels and the
ground state. In Fig. 5b, a much lower wavelength was cho-
sen for the purpose of probing the possibility of luminescence
at low energy excitation and for contrasting with that of pure
ZrO2 nanoparticles, the result showed that one emission peak
was centered at 513 nm in the PL spectrum. Compared with PL
emission for pure ZrO2 nanoparticles [30], increase of energy
Hard aggregates will come into being from those agglomer-
ates in the post-synthesis treating process if too many hydroxyl
groups exist on surface of the particles (step III). Ethanol is a
solvent with low dielectric constant (equals to 25.3 at 20 ◦C) and
the ε value will decrease sharply when temperature for its stand-
ing is uplifted (20.21 at 55 ◦C) [36], as a result, it was adapted
as the solvothermal reaction media in the synthesis process and
was used as the dispersion solvent in the post-synthesis dry-
ing process to avoid the aggregate effect in the high ε (66.73 at
60 ◦C) aqueous media. The product revealed to have remained
its topology in sub-micro scale agglomerates rather than further
evolved into hard spheres, the result again verified the DLVO
theory and suggested that ethanol is fairly well for solvothermal
synthesize of ZrO2 nanomaterials.
ZrO2 is an active and typical photon absorber and photocata-
lyst among wide band gap (Eg) metal oxides, it has two permitted
direct band to band transitions at 5.2 and 5.79 eV [37], but the
width of energy gap varies from 3.25 to 5.8 eV with variation
of different synthesis techniques [38]. UV–vis absorption and
diffuse reflectance spectra are useful skills for evaluating the
direct band gap of materials, so they were introduced here to
evaluate the energy transitions of the as-prepared sample. The
UV–vis absorption and diffuse reflection spectrum of 4YDZ
nanoparticles was observed in the region of 190–900 nm, which
was shown in Fig. 4, a strong absorption peak was observed at
wavelength of about 197 nm and a relatively weaker adsorption
increment appeared at wavelength of 275 nm, the corresponding
reflecting decrement peaks were observed at the same wave-
length. The absorption edge of each band could be obtained
Fig. 4. UV–vis absorption and reflection spectra of 4YDZ sample.
Fig. 5. PL spectra of the 4YDZ sample excited at (a) 260 nm and (b) 420 nm.

478
H. Yang et al. / Journal of Alloys and Compounds 458 (2008) 474–478
of emission phonons were observed for the 4YDZ sample both
to the higher UV excitation and the relatively lower violet-blue
light excitation.
[4] R.I. Merino, V.M. Orera, O. Povill, et al., J. Phys. Chem. Solids 58 (1997)
1579–1585.
[5] H.R. Chen, J.L. Shi, Y. Yang, Appl. Phys. Lett. 81 (2002) 2761–2763.
[6] T.C. Valmalette, M. Isa, Chem. Mater. 14 (2002) 5098–5102.
[7] J. Widoniak, S.E. Assmann, G. Maret, Eur. J. Inorg. Chem. (2005)
3149–3155.
[8] R. Sharma, D. Naedele, E. Schweda, Chem. Mater. 13 (2001) 4014–4018.
[9] H. Chen, J. Gu, J. Shi, et al., Adv. Mater. 17 (2005) 2010–2014.
[10] P.M. Kelly, L.R.F. Rose, Prog. Mater. Sci. 47 (2002) 463–557.
[11] S. Deville, G. Guenin, J. Chevalier, Acta Mater. 52 (2004) 5709–5721.
[12] J. Tang, F. Zhang, P. Zoogman, et al., Adv. Funct. Mater. 15 (2005)
1595–1602.
[13] A. Kaiser, A.J. Feighery, D.P. Fagg, et al., Ionics 4 (1998) 215–219.
[14] A. Madubuonu, H. Drings, R. Roewer, et al., Phys. Status Solidi A 203
(2006) R64–R65.
[15] J. Thornton, A. Majumdar, G. McAdam, Surf. Coat. Technol. 94/95 (1997)
112–117.
[16] B. Bolhimi, A. Morales, A.G. Ruiz, J. Solid State Chem. 142 (1999)
409–418.
[17] B. Savoini, D. Caceres, I. Vergara, et al., J. Nucl. Mater. 277 (2000)
199–203.
[18] R. Jossen, M.C. Heine, S.E. Pratsinis, et al., Chem. Vap. Depos. 12 (2006)
614–619.
As large amount of surface defects should exist on the as-
synthesized 4YDZ nanoparticles because of their high surface
area, amongst these defects the existence of surface and inner
oxygen vacancies should take the most responsibility for the
photoluminescence phenomenon of the 4YDZ sample, as they
will induce the formation of new energy levels in the band-
gap. The emission under violet-blue excitation is the evidence
of new level exists in the band-gap. The emission is induced from
the electrons on mid-gap trap states radiative relaxation to the
ground state. Formation of oxygen vacancies can be attributed
to intrinsic oxygen desorption (as illustrated as formula (6)) and
to dopants caused nonstoichiometry (formula (7)):
OO = 2O2 + 2e− + VO
(6)
••
Y3+
Zr4+−→ YZr + 2VO
(7)
••
where OO is a oxygen atom in regular site, e− an electron in con-
duction band, VO•• the doubly positive ionized oxygen vacancy,
and YZr is the singly negative ionized substitution site when a
Zr (IV) was substituted by Y(III).
[19] R. Ramamoorthy, D. Sundararaman, S. Ramasamy, Solid State Ionics 123
(1999) 271–278.
[20] H. Cao, X. Qiu, B. Luo, et al., Adv. Funct. Mater. 14 (2004) 243–246.
[21] Y.Y. Huang, B.Y. Zhao, Y.C. Xie, Appl. Catal. A 172 (1998) 327–331.
[22] H. Xu, D.H. Qin, Z. Yang, et al., Mater. Chem. Phys. 80 (2003) 524–
528.
4. Conclusions
[23] R. Piticescu, C. Monty, D. Millers, Sensor Actuat. B 109 (2005) 102–
106.
[24] J.C. Vartuli, J.G. Santiesteban, P. Traverso, et al., J. Catal. 187 (1999)
131–138.
[25] C.S. Kim, B.K. Moon, J.H. Park, et al., J. Cryst. Growth 254 (2003)
405–410.
[26] R. Reisfeld, M. Zelner, A. Patra, J. Alloy. Compd. 300/301 (2000) 147–151.
[27] B. Savoini, C. Ballesteros, J.E.M. Santiuste, et al., Phys. Rev. B 57 (1998)
13439–13447.
[28] N.G. Petrik, D.P. Taylor, T.M. Orlando, J. Appl. Phys. 85 (1999)
6770–6776.
[29] K. Hachiya, H. Oku, J. Kondoh, Phys. Rev. B 71 (2005) 064111.
[30] J. Liang, Z. Deng, X. Jiang, et al., Inorg. Chem. 41 (2002) 3602–3604.
[31] A.V. Virkar, J.-F. Jue, Method for forming t’-phase zirconia for high tem-
perature applications, US Patent 6,168,745, January 2, 2001.
[32] S. Tsunekawa, S. Ito, Y. Kawazoe, et al., Nano Lett. 3 (2003) 871–875.
[33] A. Clearfield, G.P.D. Serrette, A.H. Khazi-Syed, Catal. Today 20 (1994)
295–312.
[34] Z.L. Hua, X.M. Wang, P. Xiao, et al., J. Eur. Ceram. Soc. 26 (2006)
2257–2264.
[35] R. Hogg, T.W. Healy, D.W. Fuerstenau, Trans. Faraday Soc. 62 (1966)
1638–1651.
This work involved solvothermal synthesize of spherical
yttria-doped zirconia nanopowders with an average diameter
of about 10 nm. The nanoparticles had a soft-aggregation with
about 120 nm spheres. Band gaps for the two direct band transi-
tions indicated a red shift. PL emission was observed under both
UV excitation and violet-blue excitation, at least five levels of
energy were observed for the electrons excited by UV light, and
the shorter wavelength excited PL emission was recognized as
evidence of oxygen vacancy in the ZrO2 lattice.
Acknowledgements
This work was supported by Program for New Century
Excellent Talents in University (NCET-05-0695), Program of
Innovative Education for undergraduates in Central South Uni-
versity (2005-93-23, 2006-9-ZE009) and Mittal Innovative Key
Project (05M003).
[36] J.A. Dean, Lange’s Handbook of Chemistry, 15th ed., Mcgraw-hill, Inc.,
New York, 1999.
References
[37] A.V. Emeline, N. Serpone, Chem. Phys. Lett. 345 (2001) 105–110.
[38] S.G. Botta, J.A. Navıo, M.C. Hidalgo, et al., J. Photochem. Photobio. A
129 (1999) 89–99.
[39] K. Chee-Kin, R.A. Carolyn, J. Vacu. Sci. Technol. A 8 (1990) 3345–
3346.
[1] Z. Wang, B. Yang, Z. Fu, et al., Appl. Phys. A 81 (2005) 691–694.
[2] G.J. Rhee, J.O. White, A. Lee, et al., J. Appl. Phys. 90 (2001) 6110–6113.
[3] M.R. Davolos, S. Feliciano, A.M. Pires, et al., J. Solid State Chem. 171
(2003) 268–272.
[40] J. Liang, X. Jiang, G. Liu, et al., Mater. Res. Bull. 38 (2003) 161–168.