Relationship between the local structure and spontaneous emission probability of Er3+ in silicate, borate, and phosphate glasses

Abstract

Extended X-ray absorption fine structure (EXAFS) measurements have been performed on Er31 in silicate, borate, and phosphate glasses in order to investigate the local structure surrounding the Er31.Er31 ions coordinate to non-bridging oxygen ion sites, where alkali or alkaline earth ions terminate the network structure of silicate glasses. In borate glasses, the local structure surrounding Er31 ions is altered by the structural change ofthe borate anion. Er31 ions coordinate to non-bridging oxygen ion sites and BO4 structural units in the cases with and without the formation of non-bridging oxygen, respectively. The former is similar to the case in silicate glasses. Er31 ions selectively coordinate to the PyO site regardless of the glass composition variation. A correlation was observed between the spontaneous emission probability for 4I13/2 → 4I15/2 transition of Er3+ and the average Er–O distance calculated by EXAFS analysis. It shows the maximum value near 2.32 Å, and we conclude that the overlapping radial integral of the 4f and 5d orbitals of Er3+ would be the largest at the optimum Er31– O22 distance 2.3 Å.