UP-CONVERSION IN TM3+-DOPED ZBLAN GLASSES

Upconversion emission spectra (at 650 nm excitation) and excitation spectra (from 620-680 nm) are presented for Tm-doped ZBLAN glasses. Two blue emission bands become apparent with maxima at 450 and 480 nm. The proposed upconversion mechanism explains the spectra and is in agreement with the observed quadratic dependence of the intensities of both emission bands with excitation power. Cross-relaxation processes, decreasing the upconversion efficiency, become active for Tm concentrations above 0.2 mol%.