EPR and optical spectroscopy of Cr3+ ions in Y3Ga5O12 crystalline thin films

The emission spectrum of Cr³⁺ in Y₃Ga₅O₁₂ crystalline thin films at 10K is composed of the sharp R₁-line, its phonon sideband, and the very weak broadband. The lineshape of R₁-line at the peak wavelength of 689.8 nm cannot be fitted to a single Gaussian. This suggests that there exist several different Cr³⁺ sites in the thin film. This fact is confirmed by lifetime measurements; the radiative decay of the fluorescence is decomposed into multiple-exponential curves. The dominant component (2.8 ms) of the decay curve for the broadband emission is equal to those (2.4 ms) for R₁-line and its phonon sidebands. This result is discussed in terms of a tunneling model.