Spectroscopic studies on multiphoton processes in erbium doped fluoride and oxide glasses

Abstract

Spectroscopic analyses of the multiphoton process in erbium doped fluoride and telluride glasses (60TeO 2–25BaO–10ZnO–4YO 3/2–1ErO 3/2 and 40AlF 3–22BaF 2–22CaF 2–15YF 3–1ErF 3 in mol%) were carried out by monitoring the upconversion luminescence with excitation spectra and time-resolved luminescence decays. The two-step upconversion mechanisms by excited state absorption and by energy transfer are explained. Under continuous-wave excitation, the excitation profile of the Er 3+ green emission was correlated with the squared absorption spectra in the fluoride glass, indicating energy transfer upconversion. In the telluride glass, the profiles deviated because the excited state absorption from the 4I 13/2 level was larger. Under pulse excitation, the upconversion by energy transfer was larger in both glasses. To clarify the energy transfer scheme contributing to the green upconversion, the luminescence decay curves were analyzed quantitatively with proper rate equations and calculations of the radiative decay rates. The intermediate level was attributed uniquely to be the 4I 11/2 in both telluride and fluoride glasses.