Structure around the Tm 3+ ion in a glass based on AlF 3

Abstract

Absorption and emission spectra of a Tm 3+-doped glass based on AlF 3 were estimated from crystal-field parameters based on crystal-field theory and Judd–Ofelt theory. On the basis of point charge approximation, two kinds of crystal-field parameters were obtained from two classes of structural models prepared by using molecular dynamics (MD) simulation. In the first class the structural models were prepared from initial coordinates given at random. The calculated spectra were in agreement with the observed ones. In the second class the structural models were prepared from fixed coordination polyhedra of Tm 3+ ions. The splitting of the energy levels and emission spectra of the Tm 3+ ion were calculated from the second type of structural models. It was found that the splitting of the 3F 4 and 1G 4 levels represented the coordination number of the Tm 3+ ion, and the splitting of the 3F 4 level could be evaluated from the emission spectrum of the 1G 4– 3F 4 transition. The observed emission spectrum of the 1G 4– 3F 4 transition at 20 K resembled the emission spectrum calculated from the models of 8-fold coordinated Tm 3+ ions.