Structure and temperature effects on Nd3+ spectra in polycrystalline mixed scandium aluminum garnets Y3ScxAl5−xO12

Abstract

New spectroscopic data obtained from high resolution low temperature absorption and emission spectra of Nd3+ in mixed scandium aluminum garnets Y3ScxAl5−xO12 – (x=0–2) translucent ceramics revealed transition dependent composition effects: modification of the shapes (Lorentz at x=0 and 2, quasi-Gauss at x=1, x-dependent asymmetric for other x values, with obvious multicenter structure for low x), widths and shifts of the lines. Nd3+ electronic structure dependence on structural changes with composition is analyzed in terms of nephelauxetic effect and maximum splitting of manifolds: Sc3+ co-doping reduces the nephelauxetic effect, and the increase of 4F3/2 splitting from 85cm−1 (x=0) to 98cm−1 (x=2) denotes the lowering of local symmetry. The multicenter structure and inhomogeneous broadening of Nd3+ lines is attributed to crystal field distributions determined by the random occupancy of the octahedral sites by Sc3+ and Al3+. For low x (0.2) the resolved two satellites S1, S2 that accompany Nd:YAG lines are correlated to anisotropic crystal field perturbations produced by the n.n. Sc3+ by analogy to those determined by Y3+-antisites (excess of Y3+ ions that enter in octahedral sites of the melt-grown YAG crystals). The temperature evolution of the Nd3+ spectral characteristics (line intensity, shift, broadening) in the 10–300K range is analyzed in terms of thermal population of the Stark levels, of the effect on electron–phonon interaction and on lattice expansion. The relevance of the spectroscopic properties on the laser emission characteristics in these systems is discussed.