Role of Al2O3 in upconversion and NIR emission in Tm3+ and Er3+ codoped calcium fluoro phosphorous silicate glass system

In this study, the principal role of Al2O3 on the features of the photoluminescence spectra of Tm3+ ion and upconversion phenomenon in Tm3+ and Er3+ codoped CaF2−Al2O3−P2O5−SiO2 glass system has been investigated. The concentration of Al2O3 is varied from 2 to 10 mol% while that of Er3+ and Tm3+ 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 Al2O3 up to 6.0 mol%. This is attributed to the presence of Al3+ ions in octahedral positions in larger proportions. When the glasses are doped with Tm3+ ions, the blue and red emissions were observed, whereas in Er3+ doped glasses blue, green and red emissions were observed. When the glasses are codoped with Tm3+ and Er3+ 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 Al2O3. The IR emission band detected at about 1.8 μm due to 3F4→3H6 transition of Tm3+ 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.