Optical nanothermometer based on the calibration of the Stokes and upconverted green emissions of Er3+ ions in Y3Ga5O12 nano-garnets

The temperature-dependent green luminescence of Y3Ga5O12 nano-garnets doped with different concentrations of Er3+ ions has been measured from 300 to 850 K and, in more detail, in the biological range from 292 to 335 K. The green emissions were obtained by excitation under 488 nm blue or 800 nm near-infrared laser radiations. Both excitations give rise to bright green luminescence that can be seen by the naked eye, and which can be associated either with Stokes processes, i.e. multiphonon relaxations followed by green spontaneous emission, in the former case or with infrared-to-visible upconversion processes in the latter. The temperature-induced changes in the Er3+ green emissions have been calibrated for both excitations and results point to a strong dependence on the concentration of optically active Er3+ ions. The maximum value of the thermal sensitivity, 64 × 10−4 K−1 at 547 K, has been obtained for the nano-garnets doped with the lowest concentration of Er3+ ions, which is one of the highest values found in the literature. These results allow to conclude that a relatively low concentration of optically active ions is advisable and the changes induced by temperature on the green emissions are independent of the laser excitation radiation used, which is necessary to calibrate the temperature of the immediate environment of the Er3+-doped Y3Ga5O12 nano-garnets.This work have been partially supported by Ministerio de Economía y Competitividad de España (MINECO) under The National Program of Materials (MAT2010-21270-C04-02/-03, and MAT2013-46649-C4-3-P/-4-P), The Consolider-Ingenio 2010 Program (MALTA CSD2007-00045), and the Indo- Spanish Joint Programme of Cooperation in Science and Technology (PRI-PIBIN-2011-1153/DST-INT-Spain-P-38-11), and by the EU-FEDER funds. V. Venkatramu is also grateful to Council of Scientific and Industrial Research (CSIR), New Delhi for the sanction of major research project (No. 03(1229)/12/EMR-II, dated: 16th April, 2012). V. Monteseguro wishes to thank MICINN for the FPI grant (BES-2011- 044596)

Chemical pressure effects on the spectroscopic properties of Nd3+-doped gallium nano-garnets

[EN] Nd3+-doped RE3Ga5O12 (RE = Gd, Y, and Lu) nano-crystalline garnets of 40-45 nm in size have been synthesized by a sol-gel method. With the decrease of the RE atom size, the chemical pressure related to the decreasing volumes of the GaO4 tetrahedral, GaO6 octahedral and REO8 dodecahedral units drive the nano-garnets toward a more compacted structure, which is evidenced by the change of the vibrational phonon mode frequencies. The chemical pressure also increases the crystal-field strength felt by the RE3+ ions while decreases the orthorhombic distortion of the REO8 local environment. These effects alter the absorption and emission properties of the Nd3+ ion measured in the near-infrared luminescence range from 0.87 to 1.43 ¿m associated with the 4 F3/2¿4 IJ (J = 9/2, 11/2, 13/2) transitions. The 4 F3/2 luminescence decay curves show non-exponential behavior due to dipole-dipole energy transfer interactions among Nd3+ ions that increases with pressure.Authors are grateful to The Governments of Spain and India for the Indo-Spanish Joint Programme of Bilateral Cooperation in Science and Technology (PRI-PIBIN-2011-1153/DST-INT-Spain-P-38-11). Dr. Venkatramu is grateful to DAE-BRNS, Government of India for the award of DAE Research Award for Young Scientist (No. 2010/20/34/5/BRNS/2223). This work have been partially supported by MINECO under The National Program of Materials (MAT2013-46649-C4-2-P/-3-P/-4-P), The Consolider-Ingenio 2010 Program (MALTA CSD2007-00045), by Fundacion CajaCanarias (ENER-01), and by the EU-FEDER funds. V. Monteseguro wishes to thank MICINN for the FPI grant (BES-2011-044596). Authors also thank Agencia Canaria de Investigacion, Innovacion y Sociedad de la Informacion for the funds given to Universidad de La Laguna, co-financed by The European Social Fund by a percentage of 85%.Monteseguro, V.; Rathaiah, M.; Linganna, K.; Lozano-Gorrin, AD.; Hernandez-Rodriguez, MA.; Martin, IR.; Babu, P.... (2015). Chemical pressure effects on the spectroscopic properties of Nd3+-doped gallium nano-garnets. Optical Materials Express. 5(8):1661-1673. https://doi.org/10.1364/OME.5.001661S1661167358Pollnau, M., Hardman, P. ., Clarkson, W. ., & Hanna, D. . (1998). Upconversion, lifetime quenching, and ground-state bleaching in Nd3+:LiYF4. Optics Communications, 147(1-3), 203-211. doi:10.1016/s0030-4018(97)00524-5Brandle, C. D., & Barns, R. L. (1974). Crystal stoichiometry of Czochralski grown rare-earth gallium garnets. Journal of Crystal Growth, 26(1), 169-170. doi:10.1016/0022-0248(74)90223-1Venkatramu, V., Giarola, M., Mariotto, G., Enzo, S., Polizzi, S., Jayasankar, C. K., … Speghini, A. (2010). Nanocrystalline lanthanide-doped Lu3Ga5O12garnets: interesting materials for light-emitting devices. Nanotechnology, 21(17), 175703. doi:10.1088/0957-4484/21/17/175703Speghini, A., Piccinelli, F., & Bettinelli, M. (2011). Synthesis, characterization and luminescence spectroscopy of oxide nanopowders activated with trivalent lanthanide ions: The garnet family. Optical Materials, 33(3), 247-257. doi:10.1016/j.optmat.2010.10.039Krsmanović, R., Morozov, V. A., Lebedev, O. I., Polizzi, S., Speghini, A., Bettinelli, M., & Tendeloo, G. V. (2007). Structural and luminescence investigation on gadolinium gallium garnet nanocrystalline powders prepared by solution combustion synthesis. Nanotechnology, 18(32), 325604. doi:10.1088/0957-4484/18/32/325604Naccache, R., Vetrone, F., Speghini, A., Bettinelli, M., & Capobianco, J. A. (2008). Cross-Relaxation and Upconversion Processes in Pr3+ Singly Doped and Pr3+/Yb3+ Codoped Nanocrystalline Gd3Ga5O12: The Sensitizer/Activator Relationship. The Journal of Physical Chemistry C, 112(20), 7750-7756. doi:10.1021/jp711494dAntic-Fidancev, E., Hölsä, J., Lastusaari, M., & Lupei, A. (2001). Dopant-host relationships in rare-earth oxides and garnets doped with trivalent rare-earth ions. Physical Review B, 64(19). doi:10.1103/physrevb.64.195108Rodríguez-Carvajal, J. (1993). Recent advances in magnetic structure determination by neutron powder diffraction. Physica B: Condensed Matter, 192(1-2), 55-69. doi:10.1016/0921-4526(93)90108-iMonteseguro, V., Rodríguez-Hernández, P., Ortiz, H. M., Venkatramu, V., Manjón, F. J., Jayasankar, C. K., … Muñoz, A. (2015). Structural, elastic and vibrational properties of nanocrystalline lutetium gallium garnet under high pressure. Physical Chemistry Chemical Physics, 17(14), 9454-9464. doi:10.1039/c4cp05903dRay, S., León-Luis, S. F., Manjón, F. J., Mollar, M. A., Gomis, Ó., Rodríguez-Mendoza, U. R., … Lavín, V. (2014). Broadband, site selective and time resolved photoluminescence spectroscopic studies of finely size-modulated Y2O3:Eu3+ phosphors synthesized by a complex based precursor solution method. Current Applied Physics, 14(1), 72-81. doi:10.1016/j.cap.2013.07.027Nekvasil, V. (1978). The Crystal Field for Nd3+ in Garnets. Physica Status Solidi (b), 87(1), 317-323. doi:10.1002/pssb.2220870137Rodríguez-Mendoza, U. R., León-Luis, S. F., Muñoz-Santiuste, J. E., Jaque, D., & Lavín, V. (2013). Nd3+-doped Ca3Ga2Ge3O12garnet: A new optical pressure sensor. Journal of Applied Physics, 113(21), 213517. doi:10.1063/1.4809217Kaminska, A., Buczko, R., Paszkowicz, W., Przybylińska, H., Werner-Malento, E., Suchocki, A., … Saxena, S. (2011). Merging of the4F3/2level states of Nd3+ions in the photoluminescence spectra of gadolinium-gallium garnets under high pressure. Physical Review B, 84(7). doi:10.1103/physrevb.84.075483Allik, T. H., Stewart, S. A., Sardar, D. K., Quarles, G. J., Powell, R. C., Morrison, C. A., … Pinto, A. A. (1988). Preparation, structure, and spectroscopic properties ofNd3+:{La1−xLux}3[Lu1−yGay]2Ga3O12crystals. Physical Review B, 37(16), 9129-9139. doi:10.1103/physrevb.37.9129Wu, K., Yao, B., Zhang, H., Yu, H., Wang, Z., Wang, J., & Jiang, M. (2010). Growth and properties of Nd:Lu3Ga5O12 laser crystal by floating-zone method. Journal of Crystal Growth, 312(24), 3631-3636. doi:10.1016/j.jcrysgro.2010.09.029Jia, Z., Arcangeli, A., Tao, X., Zhang, J., Dong, C., Jiang, M., … Tonelli, M. (2009). Efficient Nd3+→Yb3+ energy transfer in Nd3+,Yb3+:Gd3Ga5O12 multicenter garnet crystal. Journal of Applied Physics, 105(8), 083113. doi:10.1063/1.3115442Guillot-Noel, O., Bellamy, B., Viana, B., & Gourier, D. (1999). Correlation between rare-earth oscillator strengths and rare-earth–valence-band interactions in neodymium-dopedYMO4(M=V,P, As),Y3Al5O12,andLiYF4matrices. Physical Review B, 60(3), 1668-1677. doi:10.1103/physrevb.60.1668Demidovich, A. A., Shkadarevich, A. P., Danailov, M. B., Apai, P., Gasmi, T., Gribkovskii, V. P., … Batay, L. E. (1998). Comparison of cw laser performance of Nd:KGW, Nd:YAG, Nd:BEL, and Nd:YVO 4 under laser diode pumping. Applied Physics B: Lasers and Optics, 67(1), 11-15. doi:10.1007/s003400050467Inokuti, M., & Hirayama, F. (1965). Influence of Energy Transfer by the Exchange Mechanism on Donor Luminescence. The Journal of Chemical Physics, 43(6), 1978-1989. doi:10.1063/1.1697063Lupei, V., & Lupei, A. (2000). Emission dynamics of the4F3/2level ofNd3+in YAG at low pump intensities. Physical Review B, 61(12), 8087-8098. doi:10.1103/physrevb.61.8087Maeda, K., Wada, N., Umino, M., Abe, M., Takada, Y., Nakano, N., & Kuroda, H. (1984). Concentration Dependence of Fluorescence Lifetime of Nd3+-Doped Gd3Ga5O12Lasers. Japanese Journal of Applied Physics, 23(Part 2, No. 10), L759-L760. doi:10.1143/jjap.23.l759Geusic, J. E., Marcos, H. M., & Van Uitert, L. G. (1964). LASER OSCILLATIONS IN Nd‐DOPED YTTRIUM ALUMINUM, YTTRIUM GALLIUM AND GADOLINIUM GARNETS. Applied Physics Letters, 4(10), 182-184. doi:10.1063/1.1753928Löhring, J., Nicklaus, K., Kujath, N., & Hoffmann, D. (2007). Diode pumped Nd:YGG laser for direct generation of pulsed 935 nm radiation for water vapour measurements. Solid State Lasers XVI: Technology and Devices. doi:10.1117/12.708220Maunier, C., Doualan, J. L., Moncorgé, R., Speghini, A., Bettinelli, M., & Cavalli, E. (2002). Growth, spectroscopic characterization, and laser performance of Nd:LuVO_4, a new infrared laser material that is suitable for diode pumping. Journal of the Optical Society of America B, 19(8), 1794. doi:10.1364/josab.19.00179

Nanocrystalline lanthanide-doped Lu3Ga5O12 garnets: interesting materials for light-emitting devices

Nanocrystalline Lu3Ga5O12, with average particle sizes of 40 nm, doped with a wide variety of luminescent trivalent lanthanide ions have been prepared using a sol\u2013gel technique. The structural and morphological properties of the powders have been investigated by x-ray powder diffraction, high resolution transmission electron microscopy and Raman spectroscopy. Structural data have been refined and are presented for Pr3+, Eu3+, Gd3+, Ho3+, Er3+ and Tm3+ dopants, while room temperature excited luminescence spectra and emission decay curves of Eu3+-, Tm3+- and Ho3+-doped Lu3Ga5O12 nanocrystals have been measured and are discussed. The Eu3+ emission spectrum shows typical bands due to 5D0 \u21927FJ (J = 0, 1, 2, 3, 4) transitions and the broadening of these emission bands with the non-exponential behaviour of the decay curves indicates the presence of structural disorder around the lanthanide ions. Lanthanide-doped nanocrystalline Lu3Ga5O12 materials show better luminescence intensities compared to Y2O3, Gd3Ga5O12 and Y3Al5O12 nanocrystalline hosts. Moreover, the upconversion emission intensity in the blue-green region for the Tm3+- and Ho3+-doped samples shows a significant increase upon 647.5 nm excitation with respect to other common oxide hosts doped with the same lanthanide ions

Bright white upconversion emission from Tm3+/Yb3+/Er3+ doped Lu3Ga5O12 nanocrystals

We report the synthesis of Tm3+/Yb3+/Er3+-doped Lu3Ga5O12 nanocrystals prepared by a simple sol-gel method exhibiting bright white light following excitation with lower energy near-infrared light (lambda(exc) = 980 nm) via an upconversion process. The combination of upconverted blue (from Tm3+), green, and red (from Er3+) emissions resulted in the white luminescence, which is intense and visible to the naked eye at a laser power less than 30 mW (3.4 W/cm(2)). The calculated Commission internationale de l'eclairage (CIE) color coordinates, which is the standard reference for defining colors, fall well within the white region and shift only slightly with the incident laser powers indicating that the material might be promising for the development of devices such as white light lasers and LEDs

Luminescence and decay characteristics of Tb3+-doped fluorophosphate glasses

Tb3+-doped fluorophosphate glasses with the composition of P2O5–K2O–SrF2–Al2O3–x Tb4O7 (where x = 0.1, 0.5, 1.0, 2.0 and 4.0 mol%) were prepared by a conventional high temperature melt quenching technique and characterized through absorption, emission, excitation and decay measurements. From the emission studies, a strong green emission at around 546 was observed, which corresponds to the 5D4 → 7F5 transition of Tb3+ ion. Green/blue intensity ratios (IG/IB) were evaluated as a function of Tb3+ concentration and vice versa. Higher IG/IB intensity ratio confirms the higher covalency between Tb–O bond and higher asymmetry around the Tb3+ ions in the present fluorophosphate glasses. The decay curves for the 5D4 level of Tb3+ ion were measured and found that they exhibited single exponential nature irrespective to the dopant concentration. The experimental lifetime was determined using single exponential fitting and found that it increased from 2.65 to 2.95 ms when Tb3+ concentration increased from 0.1 mol% to 4.0 mol%. The derived properties were compared to the other Tb3+-doped glasses in order to see the potentiality of the material for visible laser gain media at 546 nm

Luminescence characteristics of Nd3+ - doped K-Ba-Al-fluorophosphate laser glasses

Fluorophosphate glasses of composition P2O5 + K2O + KF + BaO + Al2O3 + Nd2O3 (PKFBAN), have been prepared with three (0.1, 1.0 and 2.0 mol%) Nd3+ ion concentrations and their detailed luminescence properties have been investigated. Judd-Ofelt theory has been used to analyse the optical absorption spectrum of 1.0 mol% Nd2O3-doped PKFBAN glass and evaluated the radiative properties. The predicted radiative lifetime of the F-4(3/2) level is found to be 348 mu s, which is slightly larger than the measured lifetime of 286 mu s. The measured lifetime of the F-4(3/2) level is found to decrease from 359 to 227 lis when the Nd2O3 ions concentration is increased from 0.1 to 2.0 mol%. The observed non-exponential nature of the decay curves is attributed to energy transfer between Nd3+ ions through dipole-dipole interaction. The systematic analysis yielded improved laser properties in K-Ba-Al-fluorophosphate glass with respect to those of K-Ba-Al-phosphate glasses

Composition and concentration dependence of spectroscopic properties of Nd3+-doped tellurite and metaborate glasses

The spectroscopic properties of tellurite glasses of composition (in mol%) TNKNd: (70 - x)TeO2-15Nb(2)O(5)-15K(2)O-xNd(2)O(3) (x = 0.1, 1.0, 1.5, 2.0 and 2.5) and TNLNd10: 69TeO(2)-15Nb(2)O(5)-15Li(2)O-1.0Nd(2)O(3) and lithium metaborate glass of composition LBNNd10: 89LiBO(2)-10Nb(2)O(5)-1.0Nd(2)O(3) have been investigated using absorption and emission spectra and decay curve analysis. An energy level analysis has been carried out considering the experimental energy positions of the absorption and emission bands, using the free-ion Hamiltonian model. The spectral intensities have been calculated by using the Judd-Ofelt theory and in turn the radiative properties such as radiative transition probabilities, emission cross-sections, branching ratios and radiative lifetimes have been estimated. The decay curves at the lower concentrations are exponential while they show a non-exponential behavior at higher concentrations (>= 1.0 mol%) due to energy transfer processes. The effective lifetimes for the F-4(3/2) level are found to decrease with increase in Nd2O3 concentration for all the glasses under investigation. The non-exponential decay curves have been well-fitted to the Yokota-Tanimoto model with S = 6, indicating that the nature of energy transfer is of dipole-dipole type and energy migration also plays an important role. The results obtained have been compared with Nd3+-doped phosphate, fluorophosphate, lead borate, tellurite, germanate and silicate glasses and Nd3+-doped VAG ceramic and Ca2Nb2O7 crystals. (C) 2010 Elsevier B.V. All rights reserved

Structural, elastic and vibrational properties of nanocrystalline lutetium gallium garnet under high pressure

[EN] An ab initio study of the structural, elastic and vibrational properties of the lutetium gallium garnet (Lu3Ga5O12) under pressure has been performed in the framework of the density functional theory, up to 95 GPa. Pressure dependence of the elastic constants and the mechanical stability are analyzed, showing that the garnet structure is mechanically unstable above 87 GPa. Lattice-dynamics calculations in bulk at different pressures have been performed and compared with Raman scattering measurements of the nanocrystalline Tm3+-doped Lu3Ga5O12 up to 60 GPa. The theoretical frequencies and pressure coefficients of the Raman active modes for bulk Lu3Ga5O12 are in good agreement with the experimental data measured for the nano-crystals. The contributions of the different atoms to the vibrational modes have been analyzed based on the calculated total and partial phonon density of states. The vibrational modes have been discussed in relation to the internal and external modes of the GaO4 tetrahedron and the GaO6 octahedron. The calculated infrared modes and their pressure dependence are also reported. Our results show that with this nano-garnet size the sample has essentially bulk properties.This work has been supported by Ministerio de Economia y Competitividad of Spain (MINECO) under the National Program of Materials (MAT2013-46649-C4-2/3/4-P) and the Consolider-Ingenio 2010 Program (MALTA CSD2007-00045) and by the EU-FEDER funds. V. Monteseguro, V. Lavin, and V. Venkatramu are also grateful to MINECO from Spain and Department of Science and Technology of India for financial support within the Indo-Spanish Joint Programme of Cooperation in Science and Technology (DST-INT-Spain-P-38-11/PRI-PIBIN-2011-1153). V. Monteseguro wishes to thank MICINN for the FPI grant (BES-2011-044596). F.J. Manjon acknowledges financial support from Generalitat Valenciana through project GVA-ACOMP-2013-012. V. Venkatramu is grateful to DAE-BRNS, Government of India, for the DAE Research Award for Young Scientist (No. 2010/20/34/5/BRNS/2223).Monteseguro, V.; Rodriguez-Hernandez, P.; Ortiz, HM.; Venkatramu, V.; Manjón, F.; Jayasankar, CK.; Lavin, V.... (2015). Structural, elastic and vibrational properties of nanocrystalline lutetium gallium garnet under high pressure. Physical Chemistry Chemical Physics. 17(14):9454-9464. https://doi.org/10.1039/c4cp05903dS945494641714León-Luis, S. F., Muñoz-Santiuste, J. E., Lavín, V., & Rodríguez-Mendoza, U. R. (2012). Optical pressure and temperature sensor based on the luminescence properties of Nd^3+ ion in a gadolinium scandium gallium garnet crystal. Optics Express, 20(9), 10393. doi:10.1364/oe.20.010393Venkatramu, V., Giarola, M., Mariotto, G., Enzo, S., Polizzi, S., Jayasankar, C. K., … Speghini, A. (2010). Nanocrystalline lanthanide-doped Lu3Ga5O12garnets: interesting materials for light-emitting devices. Nanotechnology, 21(17), 175703. doi:10.1088/0957-4484/21/17/175703Jaque, D., & Vetrone, F. (2012). Luminescence nanothermometry. Nanoscale, 4(15), 4301. doi:10.1039/c2nr30764bSpeghini, A., Piccinelli, F., & Bettinelli, M. (2011). Synthesis, characterization and luminescence spectroscopy of oxide nanopowders activated with trivalent lanthanide ions: The garnet family. Optical Materials, 33(3), 247-257. doi:10.1016/j.optmat.2010.10.039T. Tröster , in Handbook on the Physics and Chemistry of Rare Earths, ed. K. A. Gschneidner, Jr., J.-C. G. Bünzli and V. K. Pecharsky, Elsevier Science B.V., 2003, ch. 217, vol. 33, p. 515Karato, S., Wang, Z., Liu, B., & Fujino, K. (1995). Plastic deformation of garnets: systematics and implications for the rheology of the mantle transition zone. Earth and Planetary Science Letters, 130(1-4), 13-30. doi:10.1016/0012-821x(94)00255-wSeijo, L., & Barandiarán, Z. (2014). Large splittings of the 4f shell of Ce3+ in garnets. Physical Chemistry Chemical Physics, 16(8), 3830. doi:10.1039/c3cp53549eVenkatramu, V., Luis, S. F. L., Lozano-Gorrin, A. D., Jyothi, L., Babu, P., Rodriguez-Mendoza, U. R., … Lavin, V. (2012). Structural and Luminescence Properties of Ho3+/Yb3+-Doped Lu3Ga5O12 Nano-Garnets for Phosphor Applications. Journal of Nanoscience and Nanotechnology, 12(6), 4495-4501. doi:10.1166/jnn.2012.6179Papagelis, K., Kanellis, G., Ves, S., & Kourouklis, G. A. (2002). Lattice Dynamical Properties of the Rare Earth Aluminum Garnets (RE3Al5O12). physica status solidi (b), 233(1), 134-150. doi:10.1002/1521-3951(200209)233:13.0.co;2-zPapagelis, K., Arvanitidis, J., Ves, S., & Kourouklis, G. A. (2003). Pressure evolution of the phonon modes and force constants of Tb3Al5O12 and Lu3Al5O12. physica status solidi (b), 235(2), 348-353. doi:10.1002/pssb.200301584Monteseguro, V., Rodríguez-Hernández, P., Vilaplana, R., Manjón, F. J., Venkatramu, V., Errandonea, D., … Muñoz, A. (2014). Lattice Dynamics Study of Nanocrystalline Yttrium Gallium Garnet at High Pressure. The Journal of Physical Chemistry C, 118(24), 13177-13185. doi:10.1021/jp501570cMonteseguro, V., Rodríguez-Hernández, P., Lavín, V., Manjón, F. J., & Muñoz, A. (2013). Electronic and elastic properties of yttrium gallium garnet under pressure fromab initiostudies. Journal of Applied Physics, 113(18), 183505. doi:10.1063/1.4804133Guo, H., Zhang, M., Han, J., Zhang, H., & Song, N. (2012). First principles study of structural, phonon, optical, elastic and electronic properties of Y3Al5O12. Physica B: Condensed Matter, 407(12), 2262-2266. doi:10.1016/j.physb.2012.03.011Mujica, A., Rubio, A., Muñoz, A., & Needs, R. J. (2003). High-pressure phases of group-IV, III–V, and II–VI compounds. Reviews of Modern Physics, 75(3), 863-912. doi:10.1103/revmodphys.75.863Xu, Y.-N., & Ching, W. Y. (1999). Electronic structure of yttrium aluminum garnet(Y3Al5O12). Physical Review B, 59(16), 10530-10535. doi:10.1103/physrevb.59.10530Hohenberg, P., & Kohn, W. (1964). Inhomogeneous Electron Gas. Physical Review, 136(3B), B864-B871. doi:10.1103/physrev.136.b864Blöchl, P. E. (1994). Projector augmented-wave method. Physical Review B, 50(24), 17953-17979. doi:10.1103/physrevb.50.17953Kresse, G., & Joubert, D. (1999). From ultrasoft pseudopotentials to the projector augmented-wave method. Physical Review B, 59(3), 1758-1775. doi:10.1103/physrevb.59.1758Perdew, J. P., Ruzsinszky, A., Csonka, G. I., Vydrov, O. A., Scuseria, G. E., Constantin, L. A., … Burke, K. (2008). Restoring the Density-Gradient Expansion for Exchange in Solids and Surfaces. Physical Review Letters, 100(13). doi:10.1103/physrevlett.100.136406Chetty, N., Muoz, A., & Martin, R. M. (1989). First-principles calculation of the elastic constants of AlAs. Physical Review B, 40(17), 11934-11936. doi:10.1103/physrevb.40.11934Baroni, S., de Gironcoli, S., Dal Corso, A., & Giannozzi, P. (2001). Phonons and related crystal properties from density-functional perturbation theory. Reviews of Modern Physics, 73(2), 515-562. doi:10.1103/revmodphys.73.515Beckstein, O., Klepeis, J. E., Hart, G. L. W., & Pankratov, O. (2001). First-principles elastic constants and electronic structure ofα−Pt2Siand PtSi. Physical Review B, 63(13). doi:10.1103/physrevb.63.134112J. F. Nye , Physical properties of crystals. Their representation by Tensor and Matrices, Oxford University Press, 1957K. Parlinsky , Computer code PHONON. See: http://wolf.ifj.edu.pl/phononYu, F., Yuan, D., Cheng, X., Duan, X., Wang, X., Kong, L., … Li, Z. (2007). Preparation and characterization of yttrium gallium garnet nanoparticles by citrate sol–gel method at low temperature. Materials Letters, 61(11-12), 2322-2324. doi:10.1016/j.matlet.2006.09.003Venkatramu, V., León-Luis, S. F., Rodríguez-Mendoza, U. R., Monteseguro, V., Manjón, F. J., Lozano-Gorrín, A. D., … Lavín, V. (2012). Synthesis, structure and luminescence of Er3+-doped Y3Ga5O12 nano-garnets. Journal of Materials Chemistry, 22(27), 13788. doi:10.1039/c2jm31386cMao, H. K., Xu, J., & Bell, P. M. (1986). Calibration of the ruby pressure gauge to 800 kbar under quasi-hydrostatic conditions. Journal of Geophysical Research, 91(B5), 4673. doi:10.1029/jb091ib05p04673Errandonea, D., Meng, Y., Somayazulu, M., & Häusermann, D. (2005). Pressure-induced transition in titanium metal: a systematic study of the effects of uniaxial stress. Physica B: Condensed Matter, 355(1-4), 116-125. doi:10.1016/j.physb.2004.10.030Klotz, S., Chervin, J.-C., Munsch, P., & Le Marchand, G. (2009). Hydrostatic limits of 11 pressure transmitting media. Journal of Physics D: Applied Physics, 42(7), 075413. doi:10.1088/0022-3727/42/7/075413Euler, F., & Bruce, J. A. (1965). Oxygen coordinates of compounds with garnet structure. Acta Crystallographica, 19(6), 971-978. doi:10.1107/s0365110x65004747Birch, F. (1947). Finite Elastic Strain of Cubic Crystals. Physical Review, 71(11), 809-824. doi:10.1103/physrev.71.809V. Milman , R. H.Nobes, E. V.Akhmatskaya, B.Winkler, C. J.Pickard and J. A.White, in Ab Initio Study of the Structure and Compressibility of Garnets, in Properties of Complex Inorganic Solids 2, ed. A. Meike, A. Gonis, P. E. A. Turchi and K. Rajan, Kluwer Academic/Plenum, New York, 2000, p. 417V. Monteseguro , et al., unpublishedKaminska, A., Buczko, R., Paszkowicz, W., Przybylińska, H., Werner-Malento, E., Suchocki, A., … Saxena, S. (2011). Merging of the4F3/2level states of Nd3+ions in the photoluminescence spectra of gadolinium-gallium garnets under high pressure. Physical Review B, 84(7). doi:10.1103/physrevb.84.075483M. Born and K.Huang, Dynamical Theory of Crystal Lattices, Oxford University Press, 1954Wang, J., Yip, S., Phillpot, S. R., & Wolf, D. (1993). Crystal instabilities at finite strain. Physical Review Letters, 71(25), 4182-4185. doi:10.1103/physrevlett.71.4182Hua, H., Mirov, S., & Vohra, Y. K. (1996). High-pressure and high-temperature studies on oxide garnets. Physical Review B, 54(9), 6200-6209. doi:10.1103/physrevb.54.6200Pugh, S. F. (1954). XCII. Relations between the elastic moduli and the plastic properties of polycrystalline pure metals. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 45(367), 823-843. doi:10.1080/14786440808520496Arvanitidis, J., Papagelis, K., Christofilos, D., Kimura, H., Kourouklis, G. A., & Ves, S. (2004). High pressure Raman study of Y3Al5O12. physica status solidi (b), 241(14), 3149-3154. doi:10.1002/pssb.200405230Hurrell, J. P., Porto, S. P. S., Chang, I. F., Mitra, S. S., & Bauman, R. P. (1968). Optical Phonons of Yttrium Aluminum Garnet. Physical Review, 173(3), 851-856. doi:10.1103/physrev.173.85

Synthesis and luminescence properties of Er3+-doped Lu3Ga5O12 nanocrystals

The concentration-dependent luminescence properties of sol-gel-derived nanocrystalline Lu3(1-x)Er3xGa5O12 powders (where x = 0.01, 0.05 and 0.1) have been studied. Laser-excited luminescence spectra, emission decays and upconversion luminescence of Er3+-doped Lu3Ga5O12 nanocrystalline samples have been measured. The decay curve of the (H-2(11/2), S-4(3/2)) emission exhibits a non-exponential behavior presumably due to cross-relaxation process. Moreover, near-infrared to visible upconversion luminescence has been observed in the green region for 1.0 mol% Er3+ ions in Lu3Ga5O12 nanocrystals upon 815 nm excitation. The power dependence of the anti-Stokes luminescence suggests that upconversion is probably achieved through the sequential absorption of two photons. To the best of our knowledge, this is the first report on the preparation and optical properties of Er3+-doped Lu3Ga5O12 in the form of nanocrystalline powders

Structure, morphology and optical characterization of Dy3+-doped BaYF5 nanocrystals for warm white light emitting devices

The barium yttrium fluoride BaYF5 nanocrystalline powders doped with different concentrations of Dy3+ ions have been synthesized via a hydrothermal method and studied their structural, morphological, thermal, vibrational, and optical properties. These nanopowders have been crystallized in a single phase of the tetragonal structure with the average size of around 30 nm having spherical shape in morphology. Upon excitations at 350 and 387 nm, Dy3+ -doped BaYF5 nanocrystals exhibit strong blue and yellow emissions ascribed to the F-4(9/2) -> H-6(15/2) and F-4(9/2) -> H-6(13/2) transitions, respectively. Decay curves of the F-4(9/2) level of Dy3+ ion in BaYF5 nanocrystals exhibit non-exponential nature due to the dipole-dipole interaction between Dy3+ ions, confirmed by Inokuti-Hirayama model. The quantum yield for these nanocrystals have been found to be increased from 4.64% to 11.61% as the concentration of Dy3+ ions increases from 1.0 mol% to 2.0 mol% and then decreased to 10.68% as the dopant concentration increased to 5.0 mol%. Moreover, color coordinates and correlated color temperatures have been evaluated as a function of concentration and excitation wavelength and found to be in the warm white light region for all Dy3+ concentrations