Investigation of energy transfer and frequency upconversion in Er3+/Ho3+ co-doped tellurite glasses

The energy-transfer mechanisms and frequency upconversion emissions in 0.5Er3+/xHo3+ co-doped tellurite glasses by exciting at 980 nm have been investigated. Three intense upconversion luminescence emissions are observed at around 525, 548, and 660 nm, which correspond to Er3+:2H11/2 → 4I15/2, Er3+:4S3/2 → 4I15/2 + Ho3+:5S2(5F4) → 5I8, and Er3+:4F9/2 → 4I15/2 + Ho3+:5F5 → 5I8 transitions, respectively. The upconversion emissions reach the maximum values when Ho2O3 is 0.5 mol%, and the intensities of the green and red light emissions were about 4.5 and 6 times stronger than those un-doped Ho2O3, respectively. The possible upconversion mechanisms and energy transfer between Er3+ and Ho3+ were also estimated and evaluated. All the three emissions are based on two photon absorption processes.