Articol cresteri cristale granat

1. CONDENSED MATTER
SYNTHESIS AND PRELIMINARY CHARACTERIZATION
OF ERBIUM LITHIUM NIOBIUM GALLIUM GARNET
O. TOMA1
, L. GHEORGHE1
, A.M. VLAICU2
1
National Institute for Laser, Plasma and Radiation Physics, Solid-State Quantum Electronics
Laboratory, 409 Atomistilor Street, 077125, Magurele, Jud. Ilfov, Romania,
E-mail: octavian.toma@inflpr.ro; E-mail: lucian.gheorghe@inflpr.ro
2
National Institute for Materials Physics, 105 bis Atomistilor Street, Magurele, Jud. Ilfov, Romania
Received November 29, 2010
The synthesis of a new garnet, Er3Li0.275Nb0.275Ga4.45O12 (ErLNGG), by solid-
state reaction, is reported. A comparison of the fluorescence spectra of Er3+
in ErLNGG
and in Er-doped (5 at. %) Calcium Lithium Niobium Gallium Garnet (CLNGG)
suggests an ordering of the partially disordered CLNGG when Ca2+
ions are completely
substituted by Er3+
ions.
Key words: Partially disordered crystals, CLNGG, ErLNGG.
1. INTRODUCTION
The rare-earth-doped partially disordered garnets from the calcium niobium
gallium garnet (CNGG) family are intensely studied in present due to their broad
spectral bands combined with mechanical and thermal properties superior to
glasses. Their wide absorption bands make them suitable active media for laser-
diode-pumped solid-state lasers [1-3], while their wide emission bands can be used
to obtain tunable solid-state lasers and ultrashort-pulse lasers [4-6].
Although Nd3+
and Yb3+
ions are the most interesting for these applications,
erbium-doped CNGG and calcium lithium niobium gallium garnet (CLNGG) were
also studied for the possibility of improving the laser emission on transitions 4
I11/2
→ 4
I13/2 and 4
I13/2 → 4
I15/2. To our knowledge, the investigation of the spectroscopic
parameters of these crystals was limited up to now to low dopant concentrations
[7,8].
In this paper, the solubility limit of Er3+
in CLNGG is found to be 100 at. %;
this value is proved by the synthesis of the erbium lithium niobium gallium garnet
(ErLNGG). The synthesized crystalline powder is investigated by X-ray diffraction
and optical spectroscopy. The luminescence spectra of ErLNGG are compared with
the spectra obtained in Er(5 at. %):CLNGG.
Rom. Journ. Phys., Vol. 56, Nos. 7–8, P. 928–934, Bucharest, 2011

2. 2 Characterization of erbium lithium niobium gallium garnet 929
2. EXPERIMENTAL
For the synthesis of the erbium lithium niobium gallium garnet and erbium-
doped calcium lithium niobium gallium garnet, a solid-state reaction technique was
used. A Nabertherm LHT 02/18 furnace was used for the thermal treatments.
The X-ray diffraction analysis was performed using a Bruker diffractometer
with Cu Kα1 radiation.
The luminescence spectra of the ErLNGG were obtained using a powder
sample in a quartz cuvette; the powder was obtained by grinding the synthesized
ceramic pellet in an agate mortar with pestle. For the luminescence of
Er(5%):CLNGG, a bulk crystalline sample was used.
The luminescence spectra on the transition (4
S3/2, 2
H211/2) → 4
I15/2 were
excited in UV (wavelength range 300–400 nm) using a Xe-Hg arc lamp with a
CuSO4 solution filter and a Schott UG1 glass filter. The luminescence was
collected using a concave mirror and focused on the entrance slit of a Horiba Jobin-
Yvon 1000M Series II monochromator. The detector was an EMI S-20
photomultiplier. For the recording of data we used a SR540 optical chopper and a
SR830 lock-in amplifier from Stanford Research Systems.
For the luminescence spectra of the transition 4
F9/2 → 4
I15/2, a Xe arc lamp
with the same pair of filters was used for excitation; the luminescence was focused
with a lens on the entrance slit of a 1-m Jarrell-Ash monochromator. The detector
was a similar EMI S-20 photomultiplier. For the recording of data the same setup
as above was used.
3. RESULTS AND DISCUSSION
The stoichiometric composition of the erbium lithium niobium gallium garnet
was chosen to correspond to the optimum lithium content of CLNGG [9]:
Er3Li0.275Nb0.275Ga4.45O12. For its synthesis, the following raw materials were used:
Li2CO3 (Serva International, pulvis p. a.), Nb2O5 (Johnson Matthey Chemicals Ltd.,
spectrographically standardized), Ga2O3 (Alfa Aesar, 99.999%), and Er2O3
(Aldrich Chem. Co., 99.99+%). The raw materials were mixed in the right
proportions and homogenized using an agate mortar and pestle. The mixture was
then pressed in a pellet and kept for 15 h at 900°C to decompose the Li2CO3;
afterwards, the pellet was thermally treated for 36 h at 1300°C. A polycrystalline
ceramic pellet was obtained. Polycrystalline CLNGG ceramics were obtained by
the same method [10], using CaCO3 (Riedel – de Haën, precipitated, puriss.)
instead of Er2O3.
For the synthesis of the Er(5 at. %):CLNGG crystal, the raw materials consist
of CLNGG and ErLNGG, ground and mixed in the right proportion. The mixture
was homogenized using the agate mortar and pressed in pellets. The pellets were

3. O. Toma, L. Gheorghe, A.M. Vlaicu 3930
thermally treated for 36 h at 1300°C; after the treatment, they were used for
growing an Er(5%):CLNGG single crystal by the Czochralski technique.
The growth was performed by pulling from the melt contained in a platinum
crucible of 30 mm diameter and 30 mm height, in air. The pulling rate was 2 mm/h
at a rotation rate of 20 rpm. The melting was done by induction heating at 1450° C.
The Er(5%):CLNGG single crystal was grown using a <111> - oriented seed
obtained from a preliminary platinum wire-grown crystal.
For the luminescence measurements, a parallelipiped was cut from the single
crystal.
Fig. 1 – X-ray diffraction pattern of the ErLNGG powder. The main diffraction lines are labeled
with the corresponding Miller indices.
The X-ray diffraction pattern of the ErLNGG powder is presented in Fig. 1;
the most intense diffraction lines were labeled in this figure. The relationship
between interplanar spacings and Miller indices, found from the X-ray diffraction
pattern, is given in Table 1; the peaks were identified using the data from [11]. The
results of the X-ray diffraction analysis demonstrate that the sintered ceramic
ErLNGG exhibits a garnet structure with the lattice parameter a = 12.2514 Å at
room temperature. This value is smaller than the lattice parameters found for
CLNGG (12.51 Å) and NLNGG (12.508 Å) [10]. This is in accord with the ionic
radius of Er3+
being smaller than the ionic radii of Nd3+
and Ca2+
in dodecahedral
coordination.

4. 4 Characterization of erbium lithium niobium gallium garnet 931
Fig. 2 – X-ray diffraction pattern of Er(5%):CLNGG. The main diffraction peaks are labeled
with the corresponding Miller indices.
The X-ray diffraction pattern of the powder obtained from grown
Er(5%):CLNGG is presented in Fig. 2; it is similar with the one presented in Fig. 1
and confirms the garnet structure of Er(5%):CLNGG.
Table 1
Parameters of the diffraction lines in Fig. 1: diffraction angle, interplanar spacing, intensity
(in counts and percent) and Miller indices.
2θ (º) d (Å)
Intensity
(counts)
Intensity (%) (h k l)
17.72 5 5709 21.4 (2 1 1)
20.47 4.33 1129 4.2 (2 2 0)
27.21 3.27 2773 10.4 (3 2 1)
29.13 3.06 7617 28.6 (4 0 0)
32.66 2.74 26645 100 (4 2 0)
34.3 2.61 517 1.9 (3 3 2)
35.88 2.5 13059 49 (4 2 2)
37.38 2.4 820 3.1 (4 3 1)
40.28 2.24 2729 10.2 (5 2 1)
41.66 2.17 922 3.5 (4 4 0)
45.61 1.99 2697 10.1 (5 3 2)
46.85 1.94 435 1.6 (6 2 0)

5. O. Toma, L. Gheorghe, A.M. Vlaicu 5932
Table 1 (continued)
48.08 1.89 585 2.2 (5 4 1)
50.47 1.81 626 2.3 (6 3 1)
51.64 1.77 3625 13.6 (4 4 4)
52.79 1.73 414 1.6 (5 4 3)
53.9 1.7 6891 25.9 (6 4 0)
55.02 1.67 1168 4.4 (7 2 1)
56.11 1.64 7069 26.5 (6 4 2)
59.34 1.56 762 2.9 (7 3 2)
60.38 1.53 3220 12.1 (8 0 0)
61.43 1.51 459 1.7 (7 4 1)
62.44 1.49 363 1.4 (8 2 0)
63.47 1.46 469 1.8 (6 5 3)
64.46 1.44 452 1.7 (6 6 0)
65.46 1.42 389 1.5 (7 4 3)
67.44 1.39 453 1.7 (7 5 2)
68.43 1.37 1918 7.2 (8 4 0)
70.37 1.34 3939 14.8 (8 4 2)
71.32 1.32 591 2.2 (6 5 5)
72.28 1.31 1525 5.7 (6 6 4)
73.22 1.29 413 1.6 (7 5 4)
75.11 1.26 586 2.2 (9 3 2)
76.03 1.25 361 1.4 (8 4 4)
76.97 1.24 448 1.7 (8 5 3)
77.91 1.23 385 1.4 (8 6 0)
78.82 1.21 457 1.7 (7 7 2)
79.75 1.2 613 2.3 (10 2 0)
80.65 1.19 383 1.4 (9 4 3)
82.5 1.17 616 2.3 (7 6 5)
84.32 1.15 373 1.4 (8 7 1)
85.22 1.14 2893 10.9 (8 6 4)
86.13 1.13 507 1.9 (9 6 1)
87.05 1.12 1422 5.3 (10 4 2)
89.76 1.09 577 2.2 (10 5 1)
The luminescence spectra of transitions (4
S3/2, 2
H211/2) → 4
I15/2 and 4
F9/2 → 4
I15/2
in ErLNGG are presented in Figs. 3 and 4, compared with the spectra of the same
transitions in Er(5%):CLNGG. The excited levels of lower energy presented weak
luminescence and the spectra of the transitions originating on these levels could not
be recorded using the available setups. For an easier comparison, all spectra were
normalized, respectively, at their absolute maxima. The spectra presented in the

6. 6 Characterization of erbium lithium niobium gallium garnet 933
same figure were recorded with the same resolution. As can be seen in Figs. 3 and
4, the spectra corresponding to Er(5%):CLNGG present broad lines, while the lines
corresponding to ErLNGG are narrower, denoting an ordering of the crystal at the
100 at. % concentration of Er3+
.
This increase of the order in ErLNGG can be at least partly explained by the
replacement of the Ca2+
sublattice, ocuppied in Er(5%):CLNGG by a random
distribution of Er3+
and Ca2+
ions, by an ordered sublattice of Er3+
ions in ErLNGG.
The only type of disorder that remains is due to the random distribution of Li+
,
Nb5+
and Ga3+
cations in the three cationic coordination spheres closest to Er3+
[12,13].
Fig. 3 – Normalized luminescence spectra of transition (4
S3/2, 2
H211/2) → 4
I15/2
in ErLNGG (black line) and Er(5%):CLNGG (gray line).
Fig. 4 – Normalized luminescence spectra of transition 4
F9/2 → 4
I15/2
in ErLNGG (black line) and Er(5%):CLNGG (gray line).

7. O. Toma, L. Gheorghe, A.M. Vlaicu 7934
4. CONCLUSIONS
A new garnet, Er3Li0.275Nb0.275Ga4.45O12, was synthesized by a solid-state
reaction technique. The X-ray diffraction analysis confirms its garnet phase; the
lattice parameter is 12.2514 Å at room temperature, and the diffraction lines were
identified. A preliminary analysis of the fluorescence of this garnet suggests that
the disorder of Er-doped CLNGG is partly removed by the complete substitution of
Ca2+
with Er3+
.
Acknowledgements. The authors are indebted to Dr. S. Georgescu for useful discussions and
suggestions.
This work was supported by the project no. 159/13.08.2010 of the Romanian National Council
of the Scientific Research in Universities (CNCSIS).
REFERENCES
1. Y. X. Shi, Q. A. Li, D. X. Zhang, B. H. Feng, Z. G. Zhang, H. J. Zhang, J. Y. Wang, Opt.
Commun. 283, 2888–2891 (2010).
2. H. H. Yu, H. J. Zhang, Z. P. Wang, J. Y. Wang, Y. G. Yu, Z. B. Shi, X. Y. Zhang, M. H. Jiang,
Optics Express 17, 19015–19020 (2009).
3. K. N. He, Z. Y. Wei, D. H. Li, Z. G. Zhang, H. J. Zhang, J. Y. Wang, C. Q. Gao, Optics Express
17, 19292–19297 (2009).
4. G. Q. Xie, L. J. Qian, P. Yuan, D. Y. Tang, W. D. Tan, H. H. Yu, H. J. Zhang, J. Y. Wang, Laser
Physics Letters 7, 483–486 (2010).
5. A. Schmidt, U. Griebner, H. J. Zhang, J. Y. Wang, M. H. Jiang, J. H. Liu, V. Petrov, Opt.
Commun. 283, 567–569 (2010).
6. G. Q. Xie, D. Y. Tang, W. D. Tan, H. Luo, H. J. Zhang, H. H. Yu, J. Y. Wang, Opt. Lett. 34, 103–105
(2009).
7. A. V. Malov, P. A. Ryabochkina, A. V. Popov, E. V. Bol'shakova, Quantum Electron. 40, 377–380
(2010).
8. Yu. K. Voronko, S. B. Gessen, N. A. Eskov, V. V. Osiko, A. A. Sobol, S. N. Ushakov, L. I. Tzimbal,
Russ. J. Quantum Electron. (Kvantovaia Elektronika) 17, 721 (1990).
9. Y. M. Yu, V. I. Chani, K. Shimamura, T. Fukuda, J. Crystal Growth 171, 463–471 (1997).
10. L. Gheorghe, M. Petrache, V. Lupei, J. Crystal Growth 220, 121–125 (2000).
11. E. L. Dukhovskaya, Y. G. Saksonov, A. G. Titova, Izv. Akad. Nauk SSSR, Neorg. Mater. 9, 809
(1973).
12. A. Lupei, V. Lupei, L. Gheorghe, L. Rogobete, E. Osiac, A. Petraru, Optical Materials 16, 403–411
(2001).
13. Yu. K. Voronko, A. A. Sobol, A. Ya. Karasik, N. A. Eskov, P. A. Rabochkina, S. N. Ushakov,
Optical Materials 20, 197–209 (2002).