Optical spectroscopy of Sm3+ in C2 and C3i sites of Y2O3 ceramics

Abstract

The Sm3+ optical spectra in Y2O3 translucent ceramics are dominated by electric-dipole transitions connected to the centers of C2 symmetry, similar to those reported for single crystals. However, quasi-selective time-resolved excitation and emission spectroscopy investigation evidenced, for the first time, additional lines in the magnetic dipole allowed 6H5/2 → 4G5/2, 4F5/2 and 4G5/2 → 6H5/2, 7/2 transitions, associated with the centrosymmetric C3i centers. An energy level scheme for C3i and an improved one for C2 centers are proposed. The 4G5/2 emission lifetimes of these two structural centers (1.48 ms for C2 and 8.4 ms for C3i at 300 K) as well as the emission quenching are quite distinct, whereas Sm3+ ions in C2 centers are involved both in intra-center C2 → C2 cross-relaxation on intermediate levels and inter-center C2 ↔ C3i energy transfers (that imply only Stark levels of the ground 6H5/2 and metastable 4G5/2 manifolds), Sm3+ ions in C3i sites can participate only in the last processes. The spectroscopic data determined in this work (energy level structures, absorption and emission cross-sections, de-excitation processes parameters) suggest the prospect of Sm-doped Y2O3 ceramics as phosphor or four-level laser active materials on the highest intensity line at 608 nm in the 4G5/2 → 6H7/2 transition under GaN diode laser (~405 nm) pumping or as suppressors of amplified one-micron spontaneous emission for the Nd:Y2O3 lasers.