Synthesis, Luminescence and Nonlinear Optical Properties of Homoleptic Tetracyanamidogermanates ARE[Ge(CN2)4] (A = K, Cs, and RE = La, Ce, Pr, Nd, Sm, Eu, Gd)

Article abstract of DOI:10.1002/zaac.201600353

Two new series of tetracyanamidogermanates were prepared by solid-state reaction of appropriate amounts of REF₃ (RE = rare earth), A₂[GeF₆] (A = alkaline), and Li₂(CN₂) in evacuated silica tubes. Powder X-ray diffraction patterns of crystalline samples of KRE[Ge(CN₂)₄] and CsRE[Ge(CN₂)₄] were indexed isotypically to KRE[Si(CN₂)₄] and RbRE[Ge(CN₂)₄], respectively. Luminescence properties of Ce³⁺, Eu³⁺, and Tb³⁺ doped compounds and non-linear optical properties (NLO) of KRE[Ge(CN₂)₄] are reported.

Full text of DOI:10.1002/zaac.201600353

Journal of Inorganic and General Chemistry
DOI: 10.1002/zaac.201600353
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
Synthesis, Luminescence and Nonlinear Optical Properties of
Homoleptic Tetracyanamidogermanates ARE[Ge(CN2)4]
(A = K, Cs, and RE = La, Ce, Pr, Nd, Sm, Eu, Gd)
Konstantin Dolabdjian,[a] Christine Schedel,[a] David Enseling,[b] Thomas Jüstel,[b] and Hans-Jürgen Meyer*[a]
Abstract. Two new series of tetracyanamidogermanates were prepared
by solid-state reaction of appropriate amounts of REF3 (RE = rare
earth), A2[GeF6] (A = alkaline), and Li2(CN2) in evacuated silica tubes.
KRE[Ge(CN2)4] and CsRE[Ge(CN2)4] were indexed isotypically to
KRE[Si(CN2)4] and RbRE[Ge(CN2)4], respectively. Luminescence
properties of Ce3+, Eu3+, and Tb3+ doped compounds and non-linear
Powder X-ray diffraction patterns of crystalline samples of optical properties (NLO) of KRE[Ge(CN2)4] are reported.
Carbodiimide compounds have shown photoluminescence
properties, most remarkably for lanthanide (Ln) doped
RE2(CN2)3:Ln and Sr(CN2):Ln compounds.[5]
Introduction
Rare earth (RE) carbodiimide compounds are typically pre-
pared by solid-state metathesis reactions from RECl3 and
In 2008 the first tetracyanamidometallate was established by
Li2(CN2), allowing for various compositions of compounds.[1]
a modified solid-state metathesis reaction, revealing the char-
Reactions were investigated by thermal (DSC or DTA) studies,
acteristic [Si(CN2)4]n– ion.[6] This ion may be compared to the
revealing typical ignition temperatures of the metathesis in the
orthosilicate ion in a similar way as the condensed compound
range 450–600 °C.[2] Essentially, the same way of reaction
[7]
Si(CN2)2 may be related to SiO2.
may be applied to some carbodiimides of the first row of tran-
sition metals from Cr–Cu,[3] although their limited thermal sta-
bility sometimes requires more gentle preparation pro-
cedures.[4]
ARE[Si(CN2)4] (A = alkali, RE = rare earth) compounds ap-
pear chemically highly inert and Ln-doped (Ln = Ce, Eu, Tb)
compounds have shown remarkable photoluminescence prop-
erties.[8] Since then, the group of cyanamidometallates was at-
tributed with new representatives (Table 1), such as aluminates
LiEA2[Al(CN2)4],[9] gallates LiSr2[Ga(CN2)4],[10] and ger-
Crystal structures of all these compounds denoted herein as
carbodiimides may in fact involve the presence of carbo-
diimide [(N=C=N)2–] or cyanamide [(N–CϵN)2–] ions de-
pending on the packing arrangement with cations in structures. manates ARE[Ge(CN2)4].[11]
Table 1. Tetracyanamidometallate compounds containing the characteristic [M(CN2)4]n– ion.
Formula
Example(s)
Space group
Literature
ARE[Si(CN2)4]
ARE[Si(CN2)4]
ARE[Ge(CN2)4]
ARE[Ge(CN2)4]
ARE[Ge(CN2)4]
LiEA2[Al(CN2)4]
LiEA2[Al(CN2)4]
LiEA2[Ga(CN2)4]
A = K; RE = La–Gda,b)
A = Rb, Cs; RE = Y, La–Lua)
A = K; RE = La–Gda)
A = Rb; RE = La, Pr, Nd, Gd
A = Cs; RE = La–Lua)
EA = Sr, Eu
P21212
I4
[6a]
[6]
This work
[11]
This work
[9a]
¯
P21212
¯
I4
¯
I4
C2/c
P212121
C2/c
EA = Ba
EA = Sr
[9b]
[10]
a) Except Pm. b) Except Eu.
After silicates and germanates have shown good lumines-
cence properties[6b,11], this work’s subject is to introduce two
new series of tetracyanamidogermanates ARE[Ge(CN2)4] with
A = K, Cs and RE = La – Gd including studies of their photo-
luminescence and second harmonic generation properties.[11]
* Prof. Dr. H.-J. Meyer
E-Mail: juergen.meyer@uni-tuebingen.de
[a] Abteilung für Festkörperchemie und Theoretische Anorganische
Chemie
Institut für Anorganische Chemie
Universität Tübingen
Auf der Morgenstelle 18
72076 Tübingen, Germany
[b] Fachbereich Chemieingenieurwesen
FH Münster
Results and Discussion
Stegerwaldstraße 39
48565 Steinfurt, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201600353 or from the au-
thor.
The formation of ARE[Ge(CN2)4] compounds essentially in-
volves a solid-state reaction in which six fluoride ions of
[GeF6]2– are substituted by four carbodiimide ions.
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This reaction and the formation of ARE[Ge(CN2)4] com-
pounds is possible due to an in situ formed flux under moder-
ate temperature conditions, as has been previously reported on
basis of DTA studies.[2,11]
All preparations are performed by the same way of synthesis
shown in Equation (1). Doped ARE[Ge(CN2)4] compounds
were prepared by partial substitution of the rare earth ions by
5 mol% Ce3+, Eu3+, or Tb3+, employed as trifluorides in reac-
tions:
4Li2(CN2) + A2[GeF6] + REF3 Ǟ ARE[Ge(CN2)4] + 8LiF + AF (1)
Figure 2. Simulated XRD powder pattern of CsPr[Si(CN2)4] (black),
simulated with lattice parameters of CsPr[Ge(CN2)4] (red), recorded
Crystalline powders with a body color range from white to
grey were analyzed by XRD powder diffraction after AF pattern of CsPr[Ge(CN2)4] (blue) and LiF (green).
washed out with water. LiF remained as a side phase, due to
its poor solubility in water.
The powder patterns of KRE[Ge(CN2)4] compounds were
The patterns were compared to the homologous tetracyan-
indexed isotypically to KRE[Si(CN2)4], crystallizing in the
space group P21212. An example is shown for KPr[Ge(CN2)4]
(Figure 1).
amidosilicates as well as to their own simulated pattern for a
better visualization. Diffraction patterns of both compounds
were simulated using the atomic coordinates of the homolo-
gous KPr[Si(CN2)4] and CsPr[Si(CN2)4] and applying the in-
dexed cell parameters of the corresponding tetracyanamidoger-
manates. The experimental data is in good accordance with
the simulated data, however the reflections of KPr[Ge(CN2)4]
broaden strongly and vary in their intensity, which is probably
the result of a lower crystallinity and particle orientation.
All indexed lattice parameters are shown in Table 2 for
KRE[Ge(CN2)4] and Table 3 for CsRE[Ge(CN2)4].
The reflections were indexed within a deviation of the calcu-
lated and experimental values (2θ window) of 0.01.
The FOM was calculated with the program WinXPOW and
is defined by de Wolff.[12] The number N of single indexed
reflection and therefore the FOM vary due to different crystal-
linity of the products. They are in good agreement within each
Figure 1. Simulated XRD powder pattern of KPr[Si(CN2)4] (black),
simulated with lattice parameters of KPr[Ge(CN2)4] (red), recorded
pattern of KPr[Ge(CN2)4] (blue) and LiF (green).
CsRE[Ge(CN2)4] was processed in the same manner, but in- series, but can not be compared among the different space
¯
dexed isotypic to CsRE[Si(CN2)4] in space group I4 (Figure 2). groups.
Table 2. Lattice parameters /Å and unit cell volumes /Å3 of KRE[Ge(CN2)4] series with RE = La – Gd in space group P21212 and the number
N of single indexed reflections.
a
b
c
V
N
FOM
La
Ce
Pr
Nd
Sm
Eu
Gd
9.4785(8)
9.4668(6)
9.4657(6)
9.4415(7)
9.3900(5)
9.3290(7)
9.3103(5)
7.6824(7)
7.6229(6)
7.5781(4)
7.5566(5)
7.5312(4)
7.5296(5)
7.5143(5)
6.9977(5)
6.9483(4)
6.9105(4)
6.8720(7)
6.8241(3)
6.7886(5)
6.7476(7)
509.55(9)
501.42(7)
495.70(7)
490.29(9)
482.58(6)
476.85(8)
472.06(7)
26
29
31
33
30
27
28
115.6
118.0
126.2
132.1
128.4
116.6
113.9
Table 3. Lattice parameters /Å, unit cell volumes /Å3 of CsRE[Ge(CN2)4] series with RE = La – Gd in space group I4, number N of single
¯
indexed reflections and FOM (Figure of merit).
a
c
V
N
FOM
La
Ce
Pr
Nd
Sm
Eu
Gd
8.6694(5)
8.6254(3)
8.6231(3)
8.5889(3)
8.5533(5)
8.5153(4)
8.5051(1)
6.9817(4)
6.9265(3)
6.9051(3)
6.8674(3)
6.8223(4)
6.7809(4)
6.7583(6)
524.73(7)
516.31(5)
513.45(5)
506.61(5)
499.11(6)
491.68(6)
488.87(2)
32
34
35
34
29
29
31
259.6
284.5
289.5
281.6
245.0
247.3
257.9
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An illustration of the lanthanide contraction for both series IR Spectroscopy
of compounds is presented in Figure 3. The approximate linear
decrease of the unit cell volume as a function of the ionic radii
is observed as expected.
The presence of the tetracyanamidogermanate anion
[Ge(CN2)4]4– can be confirmed by means of infrared spec-
troscopy, as characteristic Ge–N and [NCN]2– vibrations are
expected. Conform spectroscopic data were found for both
series (A = K, Cs), with the exemplary infrared spectrum of
KGd[Ge(CN2)4] with observed vibrational frequencies listed
in Table 4. These data are in accord with the data of
RbLa[Ge(CN2)4].[11]
Table 4. Vibrational frequencies /cm–1 for KLa[Ge(CN2)4].
δ(Ge–N–C)
ν(Ge–N4)
521
725
δ(N–C–N)
606
2δ(N–C–N)
νs(N–C–N)
νas(N–C–N)
νas + νs (N–C–N)
1188
1277
2129
3372
A linear (CN2)2– ion has 3N–5 vibrational degrees of free-
dom. Theoretically the symmetrical stretching vibration is in-
active for carbodiimide compounds in IR spectroscopy, but
usually visible due to slight distortion, as in this case the cyan-
amide form. The bending vibration at 606 cm–1 is twofold de-
generate. Also visible in the fingerprint region are the bending
vibration and the stretching vibration of the GeN4 unit and the
bending vibration of Ge–N–C, which is also reported for other
compounds.[14]
In the structure of CsGd[Ge(CN2)4] there is one crystallo-
graphic (CN2)2– unit, whereas KGd[Ge(CN2)4] comprises two
different units. Nonetheless the surroundings are too similar
to see any difference in the wavenumber of their vibrational
bands.
Figure 3. Lanthanide contraction effect in the series of
KRE[Ge(CN2)4] (black) and CsRE[Ge(CN2)4] (red) compounds for
RE = La – Gd (left – right).
The characteristic motif in all ARE[Ge(CN2)4] structures is
the isolated [Ge(CN2)4]4– ion, which can be derived from an
orthogermanate, where oxido ligands are substituted with lin-
ear cyanamido units. The nearly tetrahedral environment of
tetracyanamidometallates with the penetrating orientation of
the cyanamido ligand is rarely seen in structures of carbodi-
imides, where a closest stick packing of linear (NCN) units
usually introduces layered arrangements of structures.[1,9b,10,13]
Rare-earth ions in ARE[Ge(CN2)4] structures occupy a site
with eightfold coordination environment, which nearly re-
sembles a trigonal-dodecahedral environment (Figure 4), as
has been reported for Y3+ in Y3Al5O12, referred as garnet
structure.
Luminescence Spectroscopy
Under the UV lamp the luminescence of the doped samples
did not differ significantly from the undoped samples of
ACe[Ge(CN2)4], AEu[Ge(CN2)4] and ATb[Ge(CN2)4] (A = K,
Cs). Luminescence measurements were carried out only for
doped samples.
The emission spectra of KGd[Ge(CN2)4]:Ce3+ (Figure 5a)
and CsGd[Ge(CN2)4]:Ce3+ (Figure 5b) under 360 nm exci-
tation, respectively, show two strongly overlapping emission
bands as expected for the interconfigurational [Xe]5d1 (2D) –
2
[Xe]4f1 (2F5/2, F7/2,) transition due to the spin-orbit splitting
2
of the FJ ground state of Ce3+. The emission maxima are lo-
cated in the violet blue spectral range, viz. at 430 nm and
416 nm. We compare the decay constant of the samples with
the decay constant of LuBO3:Ce. The emission from
LuBO3:Ce is in the same range than the emission of the Ce
Figure 4. Unit cell of KLa[Ge(CN2)4] (left) and eightfold coordination
environment of the RE ion (right).
As can be seen in the following luminescence measurements samples. The emission wavelength influences the decay
both materials are well suited as host materials for RE3+ acti- constant.[15] From the decay curves of the violet-blue PL
vators. Structures with the lower space group symmetry upon 375 nm excitation a decay constant of 4.6 ns for
P21212 appear more interesting due to the absence of inversion KGd[Ge(CN2)4]:Ce3+ and 8.1 ns for CsGd[Ge(CN2)4]:Ce3+
symmetry. This is a main criterion for many properties in func- was derived. This is distinctly shorter than for the violet-blue
tional materials, which is why SHG measurements were car- emitting scintillator LuBO3:Ce3+, which has a decay time of
ried out for one representative of KRE[Ge(CN2)4] compounds. 55 ns (see Table 5). The internal quantum yield is calculated
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by dividing the decay time of the sample by the decay time of
In contrast to the intraconfigurational 4f – 4f transitions of
the radiative transition.[16] As the decay time of the radiant Eu3+ and Tb3+, which are mostly unaffected by the crystal
transition we therefore use the 55 ns of the LuBO3 exemplarily, structure, the impact on the Ce3+ luminescence is much higher
which points to severe quenching of the photoluminescence since the energetic splitting of the d-orbitals is significantly
process and to an internal quantum yield solely in the order of higher than for f orbitals. This is a possible reason for the
10%. Excitation spectra, which were monitored for the maxi- difference in the Stokes shifts. Since the Ce3+ ion is assumed
mum of the respective emission bands, show two crystal-field to occupy the Gd3+ site, corresponding to a distorted trigonal
2
components of the [Xe]4f1 – [Xe]5d1 transition at about 295 dodecahedral environment, the D term of the Ce3+ [Xe]5d1
and 360 nm. The energetic splitting of these two bands is excited state configuration is expected to split into five energy
thus 0.76 eV, whereas the Stokes shift is 0.56 eV for levels by the crystal field interaction. The lack of three exci-
KGd[Ge(CN2)4]:Ce3+ and 0.46 eV for CsGd[Ge(CN2)4]:Ce3+. tation bands points either to five bands, which are so close to
each other that they cannot be resolved, or to photoionization
after excitation into those three crystal-field components at
higher energy, since these components are close to or already
located in the conduction band. However, the excitation bands
are somewhat shifted towards lower energy in comparison to
those observed in Ce3+ doped KLa[Si(CN2)4]:Ce.[6b] This
might also explain the longer decay time and thus higher in-
ternal quantum yield of the Cs comprising compound.
The excitation spectra of both germanates doped with Eu3+
display a broad ligand-to-metal charge-transfer excitation band
at 340 nm with a width of almost 150 nm (0.92 eV). The emis-
sion spectra upon 340 nm, i.e. ligand-to-metal charge-transfer
excitation are depicted in Figure 6 and Figure 7, and show the
typical emission line patterns due to the [Xe]4f6 – [Xe]4f6 in-
traconfigurational transitions of Eu3+.[15a] The most intense
emission lines are located at 594 nm (5D0
–
7F1), 616 nm
7
7
(5D0 – F2), and 698 nm (5D0 – F4). The asymmetry ratio of
Figure 5. (a) Excitation spectrum (monitored at 430 nm) and emission
spectrum (upon 360 nm excitation) of KGd[Ge(CN2)4]:Ce3+. (b) Exci-
tation spectrum (monitored for 416 nm) and emission spectrum (upon
Figure 6. Excitation spectrum (monitored at 593.5 nm) and emission
360 nm excitation) of CsGd[Ge(CN2)4]:Ce3+
.
spectrum (upon 340 nm excitation) of KGd[Ge(CN2)4]:Eu3+
.
Table 5. Decay times for the investigated samples compared to data of typical luminescent materials from literature.
Decay τ(1/e)
Emission peaks at
Excitation peaks at
Literature
KGd[Ge(CN2)4]:Ce3+
CsGd[Ge(CN2)4]:Ce3+
4.6 ns
8.1 ns
55 ns
1.6 ms
1.7 ms
4.6 ms
1.5 ms
1.5 ms
3–4 ms
416 nm
416 nm
418 nm
593 nm
593 nm
590 nm
546 nm
546 nm
543 nm
375 nm
375 nm
360 nm
340 nm
340 nm
220 nm
257 nm
257 nm
220 nm
This work
This work
[19]
This work
This work
[17b]
This work
This work
[6] [20]
LuBO3:Ce3+
.
KGd[Ge(CN2)4]:Eu3
CsGd[Ge(CN2)4]:Eu3+
.
Y3Al5O12:Eu3+
.
KGd[Ge(CN2)4]:Tb3+
CsGd[Ge(CN2)4]:Tb3+
Lu3Al5O12:Tb3+
.
.
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the Eu3+ emission (5D0
– –
7F2 5D0 7F1) are 1.11 for (Figure 8 and Figure 9). This band is assigned to an intercon-
/
CsGd[Ge(CN2)4]:Eu3+ and 1.25 for KGd[Ge(CN2)4]:Eu3+, figurational [Xe]4f8 to [Xe]4f75d1 transition of Tb3+, while the
which points to an inversion symmetric site (D2) with little narrow band width might be caused by the high energy re-
5
7
distortion. The unusual high intensity of the D0 – F4 transi- cording limit for these measurements due to the vanishing in-
tions is sometimes observed in Eu3+ activated materials, as, for tensity of the Xe lamp in this spectral range.
example, in garnets such as YAG, LuAG, Ca3Sc2Al3O12, or
Ca2Ga2SiO7.[17] Published explanations points to an impact of
the local site symmetry and to the covalent interaction between
Eu3+ and the surrounding structural elements.[18] The exci-
tation spectra shows next to the ligand-to-metal charge-transfer
bands, distinct lines at 362, 395, 418, 465, and 527 nm, due to
the [Xe]4f6 – [Xe]4f6 transitions as assigned in Figure 6 and
Figure 7.
Figure 9. Excitation spectrum (monitored at 546 nm) and emission
spectrum (upon 257 nm excitation) of CsGd[Ge(CN2)4]:Tb3+
.
Non-linear Optics
Figure 7. Excitation spectrum (monitored at 593.5 nm) and emission
spectrum (upon 340 nm excitation) of CsGd[Ge(CN2)4]:Eu3+
Since the development of lasers is increasing rapidly, non-
linear optical properties gained great importance for adjusting
variable frequency. With high energies of the electric field, the
oscillation of the dipole moments is distorted, which leads to
a nonlinear dependency of the polarization and the terms of
higher order gain weight.
.
Emission
spectra
(Figure 8
and
Figure 9)
of
KGd[Ge(CN2)4]:Tb3+ and CsGd[Ge(CN2)4]:Tb3+ recorded
upon 257 nm excitation reveal emission line multiplets as ex-
pected for the intraconfigurational [Xe]4f8 – [Xe]4f8 transi-
tions of Tb3+ at 488, 547, 588, 622, 649, 668, and 680 nm.
P = ε0χE + ε0χ(2)E2 + ε0χ(3)E3 + …
(2)
5
7
These are assigned to the respective D4 – Fn transitions with
n = 6 – 0. Remarkable is the rather narrow excitation band at
257 nm, which is observed for both investigated compounds
where P is the polarization; ε0 is the free space electric per-
mittivity; χ is the linear susceptibility; χ(n) is the nonlinear
susceptibility of n-th order, and E is the electric field.
Regarding effects of second order, as special case of the sum
frequency generation (SFG), the second harmonic generation
(SHG) is known as frequency doubling effect.
Depending on the crystal symmetry of the dielectric me-
dium, the distortion of the dipole oscillation is symmetric or
asymmetric. For structures with inversion symmetry, the value
for the non-linear susceptibility of second order is χ(2) = 0. In
the case of non-centrosymmetric crystal symmetry the suscep-
tibility is χ(2) ϶ 0, so the SHG can occur. This structural
requirement is valid for bulk material and may not be mistaken
with surface-SHG, which can occur in centrosymmetric struc-
tures as well due to a loss of symmetry on the surface.
Non-centrosymmetric tetracyanamidometallates are candi-
dates for non-linear optical properties, similar to other com-
pounds with tetrahedral anions, such as KTiOPO4 (KTP). The
SHG properties for KLa[Ge(CN2)4] (space group P21212) were
measured with the results shown in Figure 10 and Figure 11.
Figure 8. Excitation spectrum (monitored at 546 nm) and emission
spectrum (upon 257 nm excitation) of KGd[Ge(CN2)4]:Tb3+
.
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compounds with RE = Ce, Eu, and Tb are excited under an
UV lamp supporting the assumption that dopants occupy sites
of rare-earth ions. Comparison of the lifetimes indicates a sig-
nificant quenching of the luminescence. Excitation for Eu3+
comprising compounds is not limited to forbidden 4f – 4f-
transition due to the strongly red-shifted CT band.
All compounds appeared stable in air and water as well as
organic solvents like tetrahydrofuran or ethanol up to at least
60 degree.
NLO properties are exemplarily demonstrated for
KLa[Ge(CN2)]4. Compared to the important industrial KTP
standard an SHG intensity of only 10% was obtained.
Figure 10. Logarithmic values of intensity plotted against the exitation
power at the most intensive SHG spot for KLa[Ge(CN2)4] compared
to KTiO(PO4) (KTP).
Experimental Section
Synthesis: Starting materials A2GeF6 (A = K, Cs) were prepared in
two steps.
Figure 10 displays the exponential dependency for second
order optical polarization. In the double-logarithmic plot the
condition in terms of Equation (2) is a slope of 2 for the linear
fit [Equation (3)]:
GeO2 (Chempur, 99.999%) was dissolved in hydrofluoric acid (Merck
KGaA, 38–40% extra pure) in a molar ratio of 1:6 in order to obtain
H2GeF6. One equivalent A2CO3 (K2CO3: Merck pro analysi, Cs2CO3:
Sigma-Aldrich Chemie GmbH, 99.9%) was added and A2GeF6 pre-
cipitated as a colorless solid. The products were washed with water
and dried at 80 °C in air.
lg(P) ~ lg(E)2 ~ 2lg(E)
(3)
The emission spectrum in Figure 11 points out, that there is
no coexisting effect, since the only detectable signal is the
SHG-peak at 400 nm.
The preparation of Li2(CN2) has been reported previously.[1]
The starting materials K2GeF6, Li2CN2 and REF3 (RE = La – Gd) were
mixed in a molar ratio of 1:4:1 in a dry argon atmosphere in an agate
mortar and sealed in an evacuated silica tube. The mixture was heated
in a Carbolite crucible furnace up to 575 °C with a heating rate of
2 K·min–1, remained at this temperature for 72 h before cooling the
products to room temperature with 0.5 K·min–1. The ampoules were
opened in air with notable pressure.
Doped compounds were prepared with a concentration of 5 mol%
CeF3, EuF3, or TbF3 in starting materials. The degree of incorporation
was not determined for any product.
X-ray Powder Diffraction: XRD patterns of the well grinded prod-
ucts were collected with a Stadi-P (STOE, Darmstadt) powder dif-
fractometer using germanium monochromated Cu-Kα1 radiation (λ =
154.06 pm) and a Mythen 1 K detector.
Figure 11. Emission spectrum of KLa[Ge(CN2)4] compared to KTP
with an excitation wavelength of 800 nm and an excitation power of
112 μW.
Indexing was carried out with the program WinXPOW, Version 1.10:
KLa[Ge(CN2)4] was compared with KTiOPO4 (KTP), Diffractometer Software; Stoe&Cie GmbH, Darmstadt, Germany,
2001.
which is one of the most efficient SHG-materials in applica-
tion. Since the intensity is about 10% that of KTP,
KLa[Ge(CN2)4] is not on a competitive basis and is not sub-
jected for further studies. Though, this result is a proof of prin-
ciple and yet another interesting property for cyanamide-based
compounds.
Infrared Spectra: Vibrational spectra were recorded with a Bruker
Vertex 70 spectrometer within the range of 400–4000 cm–1 by using
KBr pellets.
Luminescence Spectroscopy: Excitation spectra, emission spectra,
and decay curves were collected with a fluorescence spectrometer
FLS920 (Edinburgh Instruments, UK) equipped with a 450 W ozone
free xenon discharge lamp (OSRAM) for the excitation and emission
spectra and a picosecond pulsed diode laser from Edinburgh Instru-
ments (model – EPL375) for recording the decay curves. A sample
chamber installed with a mirror optic for powder samples. For detec-
tion a R2658P single photon counting photo multiplier tube (Hamam-
atsu) was used. All luminescence spectra were recorded with a spectral
Conclusions
The synthesis of homoleptic tetracyanamidogermanates was
accomplished by solid-state metathesis reaction.
Samples of KRE[Ge(CN2)4] and CsRE[Ge(CN2)4] doped
with Ce3+, Eu3+, and Tb3+ show characteristic luminescence.
Similar luminescence behavior is obtained when undoped resolution of 1 nm, a dwell time of 0.2 s in 1 nm steps and 3 repeats.
Z. Anorg. Allg. Chem. 0000, 0–0
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Journal of Inorganic and General Chemistry
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Zeitschrift für anorganische und allgemeine Chemie
[7] R. Riedel, A. Greiner, G. Miehe, W. Dressler, H. Fuess, J. Bill,
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to a spectroscopic unit to acquire the nonlinear spectra. Further details
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Supporting Information (see footnote on the first page of this article):
Decay measurements of the title compounds.
Acknowledgements
We like to thank Prof. Dr. A. Meixner and Dr. Xiao Wang for the NLO-
measurements. K. Dolabdjian is grateful to the Landesgraduierten-
förderung of the Ministerium für Wissenschaft, Forschung und Kunst
Baden-Württemberg (Universität Tübingen) for the support of his work
with a fellowship. Support of the Deutsche Forschungsgesellschaft
(Bonn) via grant ME914/25-2 is acknowledged.
[14] F. A. Miller, G. L. Carlson, Spectrochim. Acta 1961, 17, 977–989.
[15] a) G. Blasse, B. C. Grabmaier, Luminescent Materials; Springer,
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2001 .
Keywords: Cyanamidometallate; Luminescence; Solid-state
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Received: September 23, 2016
Published Online: ᭿
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© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Journal of Inorganic and General Chemistry
ARTICLE
Zeitschrift für anorganische und allgemeine Chemie
K. Dolabdjian, C. Schedel, D. Enseling, T. Jüstel,
H.-J. Meyer* ..................................................................... 1–8
Synthesis, Luminescence and Nonlinear Optical Properties of
Homoleptic Tetracyanamidogermanates ARE[Ge(CN2)4] (A =
K, Cs, and RE = La, Ce, Pr, Nd, Sm, Eu, Gd)
Z. Anorg. Allg. Chem. 0000, 0–0
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© 0000 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim