Correlation between emission properties, valence states of Ce and chemical compositions of alkaline earth borate glasses

Although there are many reports investigating emission properties of Ce3+ centers, there is little report on the quantitative Ce3+/(Ce3++Ce4+) ratio, which is one of the most fundamental factors for designing phosphors. In this report, we have investigated the correlation among the optical and emission properties of Ce-doped alkaline earth borate glasses with the Ce3+/(Ce3++Ce4+) ratio determined by X-ray absorption near-edge structure analyses. It is confirmed that the additional carbon increases the population of Ce3+, which is also suggested from the optical absorption edge, Eg opt, due to Ce and the quantum yield (QY). We have revealed that the Ce3+ concentration of the Sr-substituted glass is completely the same as that of the Ca-substituted one that exhibits the highest efficiency, even though the Ce3+ ratio is suggested to depend on the substitution spices from the Eg opt and QY. Therefore, we can conclude that not only the Ce3+ amount but also the local structures of Ce3+ affect the emission properties. In other words, the luminescent efficiency of the Ce3+ centers in amorphous materials strongly depends on the various local coordination states.