Influence of Tm3+ optical centers on spectroscopic properties at the 3F4-3H6 2-μm laser transition

•Tm3+ optical centers fluorescence spectra at 77K for 3F4-3H6 transition are obtained.•Tm3+ optical centers lifetimes at 77K for 3F4-3H6 transition are measured.•Tm3+ long-lifetime optical center is suggested to have tetragonal local symmetry.

Individual low temperature (77 K) fluorescence spectra of tetragonal (C4v), clustered, and long-lifetime optical centers of Tm3+ ions at the 3F4-3H6 transition are recorded and the lifetimes of these centers are measured. Analysis of the number and positions of the fluorescence lines of the long-lifetime optical center allows to suggest that it has tetragonal (C4v) local symmetry.