Crystal-Field Strength Variations and Energy Transfer in Cr3+-Doped GGG Transparent Nanoceramics

Interpretation of the spectroscopic properties of Cr3+ions in garnets is sufficiently complicated by the variation of the crystal-field strength. Occupation by Cr3+ions of octahedral sites with different local crystal-field strengths alters their emission spectra. In the present work, we report the changes in the emission spectra of Cr3+:GGG nanoceramics synthesized by the high isostatic pressure (HIP) method. The influence of the energy transfer process between Cr3+ions on their emission spectra is shown. The room temperature excitation and emission spectra are similar for the samples doped with different concentrations of Cr3+ions. At the same time, in the low-temperature emission spectra, the impact of 4T2g(4F) → 4A2g(4F) broadband emission on the overall Cr3+emission increases with Cr3+concentration. Since Racah parameters are within the measurement error for Cr3+:GGG nanoceramics, the difference in low-temperature emission spectra was explained by the increase in energy transfer between Cr3+ions, thus increasing the ratio of emission intensity of Cr3+ions in the low crystal field to the total luminescence.