Concentration-dependent luminescence of Tb3+ ions in high calcium aluminosilicate glasses

This study deals with the results on the concentration-dependent fluorescence properties of Tb3+-doped calcium aluminosilicate (CAS) glasses of composition (100−x)(58SiO2-23CaO-5Al2O3-4MgO-10NaF in mol%)-x Tb2O3 (x=0, 0.25, 0.5, 1, 2, 4, 8, 16, 24, 32, 40 in wt%). The FTIR reflectance spectra suggested the role of dopant ions as network modifiers in the glass network. The fluorescence spectra of low Tb3+-doped glasses have revealed prominent blue and green emissions from 5D3 and 5D4 excited levels to 7Fj ground state multiplet, respectively. The glass with 2 wt% of Tb2O3 has exhibited maximum intensity of blue emission from 5D3 level, while green emission from 5D4 level has increased linearly up to 24 wt% and showed reduction in the rate of increase for higher Tb2O3 concentrations. The concentration quenching of blue emission (5D3→7Fj) is attributed mainly to the resonant energy transfer (RET) assisted cross-relaxation (CR) among the excited and nearest neighbour unexcited Tb3+ ions in the glass matrix. The decline in rate of increase of green emission (5D4→7Fj) at higher concentrations has been explained due to a possible occurrence of cooperative energy transfers leading to 4f8→4f75d transition interactions. The blue and green emission decay kinetics have been recorded to compute the excited level (5D3 and 5D4) lifetimes, which confirmed the Tb3+ concentration quenching of the blue emission in these glasses.