Heavily Eu2O3-doped yttria-aluminoborate glasses for red photoconversion with a high quantum yield: luminescence quenching and statistics of cluster formation

We report on the photoluminescence (PL) properties of heavily Eu2O3 doped Y2O3-Al2O3-B2O3 glasses as a high-gain red-emitting material for photoconversion. A UV-to-red conversion efficiency of up to 60% is achieved in this material. Concentration quenching is related to the formation of -{Eu-O-Me-O-Eu}-( Me = B, Y, Al) and -{Eu-O-Eu}- linkages in the first and second coordination shell, respectively, of Eu3+. For a quantitative consideration, we employ a statistical approach to estimate the number of those species as a function of europium concentration. In this way, a crossover composition is obtained at a dopant concentration of similar to 3 mol% of Eu2O3 where further addition of europium directly increases the number of -{Eu-O-Eu}-. In the latter species, the critical distance for concentration quenching of PL is achieved so that for concentrations above the crossover, PL quantum efficiency decreases. This observation is confirmed experimentally through lifetime analyses as well as direct measurements of internal quantum efficiency. The proposed tool can now be used to predict and optimize cluster formation and concentration quenching in rare-earth doped glasses.