Low Temperature Luminescence Behavior of Trace Cr and Fe Impurities in Gd3Ga5O12 Single Crystals.

Abstract

This article examines the influence of unintentional Cr3+ and Fe3+ impurity ions on the luminescent properties of Gd3Ga5O12 (GGG) single crystals. The characteristic features of the spectra excited by high-energy synchrotron radiation in the temperature range of 10–300 K are analyzed. It is shown that at 10 K the luminescence is dominated by a narrow-band emission of Cr3+ ions arising from the spin-forbidden 2E→4A2 transition, which indicates weak electron–phonon coupling and high crystalline homogeneity. It is revealed that with increasing temperature the intensity of this transition decreases significantly, while a broadband luminescence emerges, associated with the spin-allowed 4T2→4A2 transition and the contribution of Fe3+ ion emission. The temperature evolution of the spectra is shown to result from thermal redistribution of the Cr3+ excited-state populations, interlevel state mixing, and partial removal of the spin-forbidden nature of Fe3+ transitions due to lattice vibrations. Based on the study, conclusions are drawn regarding the role of impurity centers in energy transfer and nonradiative relaxation processes. The results are of interest both for fundamental photonics and for the development of efficient luminescent materials and optical devices designed to operate over a wide temperature range.