NIR to visible upconversion in Er3+-doped fluoride glass under 1550 and 980 nm excitations

The upconversion luminescence of Er3+-doped fluoride glass under 1550 and 980 nm pumpings is investigated. The emissions pumped by 488 nm excitation is also obtained and used as a comparison. Absorption and emission spectra are tested and visible to infrared emissions (520, 550, 667, 800, 850, 980, 1535, and 2708 nm) are clearly observed. Upconversion luminescence from 980 or 1550 nm to green or red visible luminescence is a two or three-photon process, respectively. The red to green emission intensity ratios are 0.06 and 0.11 when the sample is excited under 488 and 980 nm pumpings, respectively. However, significantly brighter red emission is observed under 1550 nm pumping and the ratio is as high as 12.5, which is most decided by non-radiative decay processes between 4I9/2 and 4I11/2 levels. In addition, mechanisms of the upconversion by multiphoton absorption and energy transfer processes are discussed based on the energy-level diagram of Er3+ and upconversion luminescence spectra. These results benefit investigations on upconversion luminescence materials, particularly Er3+-doped glasses.