Temperature dependence behaviors of three-level transition in Nd3+/Al3+ Co-doped silica glass

Lasers at 900 nm originating from the three-level transition (4F3/2 → 4I9/2) of Nd3+-doped materials have become a research focus because of their application in two-photon imaging and deep-blue lasers generation using frequency-doubling. Although it is generally accepted that this three-level transition laser is more favorable at low-temperatures, we found an extraordinary temperature dependence of the three-level transition properties of Nd3+/Al3+ co-doped silica glass, i.e., the fluorescence branching ratio at 900 nm increased with increasing temperature. An analysis using Judd-Ofelt theory and energy level splitting revealed that the temperature-associated changes in electron cloud overlap and energy level splitting enhancement favored the fluorescence branching ratio at 900 nm, despite the enhanced non-radiative transitions, which generally deteriorate the emission intensity at 900, 1060 and 1330 nm. These results will improve our understanding of the temperature dependence of the three-level transition of Nd3+, and contribute to the application and development of 900 nm lasers.