The upconversion mechanism of Er3+ ions has been studied for lead-germanate glasses containing Er2O3 concentrations from 0.1 mol % to 2 mol %. Intense green emission was observed at room temperature due to 4S3/2→4I15/2 transition excited by a cw near-infrared laser beam at 797 nm. This green emission shows a similar intensity for samples with different Er3+ ion concentrations. A weak blue emission of 410 nm originating from the 2H9/2→4I15/2 transition was also observed. This blue emission and a red emission from the 4F9/2 level increase with the increase in Er3+ ion concentration. The bright green emission is attributed to the excited level absorption while the blue emission is due to a third step excitation where energy transfer between excited ions owing to their Coulomb interaction plays a key role.
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Pan et al. (1995) studied this question.
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