Role of Al 2O 3 in upconversion and NIR emission in Tm 3+ and Er 3+ codoped calcium fluoro phosphorous silicate glass system

Abstract

In this study, the principal role of Al 2O 3 on the features of the photoluminescence spectra of Tm 3+ ion and upconversion phenomenon in Tm 3+ and Er 3+ codoped CaF 2−Al 2O 3−P 2O 5−SiO 2 glass system has been investigated. The concentration of Al 2O 3 is varied from 2 to 10 mol% while that of Er 3+ and Tm 3+ is fixed. IR and Raman spectral studies have indicated that there is a gradual increase in the degree of disorder in the glass network with increase in the concentration of Al 2O 3 up to 6.0 mol%. This is attributed to the presence of Al 3+ ions in octahedral positions in larger proportions. When the glasses are doped with Tm 3+ ions, the blue and red emissions were observed, whereas in Er 3+ doped glasses blue, green and red emissions were observed. When the glasses are codoped with Tm 3+ and Er 3+ ions and excited at 790 nm, all the three emission lines were observed to be reinforced, especially in the glasses mixed with 6.0 mol% of Al 2O 3. The IR emission band detected at about 1.8 μm due to 3F 4→ 3H 6 transition of Tm 3+ ions is also observed to be strengthened due to codoping. The reasons for enhancement in the intensity of various emission bands due to codoping have been identified and discussed with the help of rate equations for various emission transitions.