Nanocrystalline Sm3+-doped Lu3Ga5O12 garnets: An intense orange-reddish luminescent material for white light emitting devices

Nanocrystalline lutetium gallium garnets Lu3Ga5O12 doped with various concentrations of Sm3+ ions have been prepared by a low-cost and environmentally benign sol-gel method. The nanocrystalline structure of the Lu3Ga5O12 garnets has been identified by X-ray powder diffraction whereas their optical properties have been investigated through laser-excited spectroscopic techniques. The diffuse reflectance spectrum of Sm3+ ions in Lu3Ga5O12 nano-garnets has been measured for predicting its partial energy level structure. The luminescence spectra of Sm3+-doped Lu3Ga5O12 nano-garnets have been measured under both 405 and 473 nm laser excitations as a function of Sm3+ ion concentration. The nano-garnets exhibit intense orange-reddish luminescence at 615 nm attributed to the 4G5/2→6H7/2 transition. The optimum molar concentration of Sm3+ ions have been found to be about 3.0 mol% with critical energy transfer distance of 16.8 Å. The luminescence decay curves of the 4G5/2 level of Sm3+ ions measured under 560 nm resonant excitation have been found to be non-exponential. The non-exponential nature of the decay curves has been analyzed by Inokuti-Hirayama model and found that the dominant mechanism of interaction between active ions is of dipole-dipole type. All these results indicate that the present nano-garnets could be useful for white light emitting devices.