Structure around the Tm3+ ion in a glass based on AlF3

Absorption and emission spectra of a Tm3+-doped glass based on AlF3 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 Tm3+ ions. The splitting of the energy levels and emission spectra of the Tm3+ ion were calculated from the second type of structural models. It was found that the splitting of the 3F4 and 1G4 levels represented the coordination number of the Tm3+ ion, and the splitting of the 3F4 level could be evaluated from the emission spectrum of the 1G4–3F4 transition. The observed emission spectrum of the 1G4–3F4 transition at 20 K resembled the emission spectrum calculated from the models of 8-fold coordinated Tm3+ ions.