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

Abstract

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 473nm laser excitations as a function of Sm3+ ion concentration. The nano-garnets exhibit intense orange-reddish luminescence at 615nm attributed to the 4G5/2→6H7/2 transition. The optimum molar concentration of Sm3+ ions have been found to be about 3.0mol% with critical energy transfer distance of 16.8Å. The luminescence decay curves of the 4G5/2 level of Sm3+ ions measured under 560nm 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.