Mechanisms and absolute quantum yield of upconversion luminescence of fluoride phosphors

Mechanisms of upconversion luminescence (UCL) of SrF2:Er phosphors corresponding to the G411/2→I415/2, H29/2→I415/2, F45/2→I415/2, F47/2→I415/2, H211/2→I415/2, S43/2→I415/2, F49/2→I415/2, and I49/2→I415/2 transitions upon excitation of the I411/2 level of Er3+ ions were investigated. Energy transfer upconversion processes are responsible for the populating of the H29/2, H211/2, S43/2, and F49/2 levels. Cooperative process is the dominant mechanism of luminescence from S43/2 and F49/2 levels for SrF2:Er with high concentrations of Er3+ ions. The UCL from G411/2 and F45/2 is explained by excited-state absorption. Cross-relaxation processes take part in the population of F49/2 and I49/2 levels. For quantifying material performance, the Er3+-concentration dependence of UCL and the absolute quantum yields of SrF2:Er were studied. The most intensive visible luminescence was obtained for SrF2:Er (14.2%) with 0.28% maximum quantum yield.