Research on the thermal-shifts and electron-phonon coupling parameters for two spectral lines in Nd3+-doped Gd3Sc2Ga3O12 and La3Lu2Ga3O12 garnets

摘要

The thermal red-shift of spectral line E 1 (R-2 - Y-3) and the thermal blue-shift of spectral line E-2 (R1 - Z5) for Nd3+ in Gd3Sc2Ga3O12 (GSGG) and La3Lu2Ga3O12 (LLGG) garnet crystals are studied by using a full expression including both the dynamic factor due to electron-phonon interaction and the static factor due to lattice thermal expansion. The results indicate that the full expression enables explaining not only the thermal red-shift, but also the thermal blue-shift. For both the spectral lines E-1 and E-2, the dynamic factor leads to the red-shift because the true electron-phonon coupling parameters alpha' are always negative, whereas the static factor results in the blue-shift due to the positive static parameter A. The observed thermal blue-shift of line E-2 for GSGG: Nd3+ and LLGG: Nd3+ is owing to the static factor being larger than the dynamic one rather than to the positive apparent electron-phonon parameter alpha obtained by a simple expression containing only the dynamic factor. The true electron-phonon parameters alpha' acquired by the full expression in sign (for line E-2) and in magnitude (for both the lines E-1 and E-2) differ from the apparent parameters a obtained from the simple expression. So, the reasonable studies of thermal-shift and electron-phonon coupling parameters should employ the full expression. (C) 2018 Elsevier GmbH. All rights reserved.