Mechanisms of fluorescence enhancement in rare earth sol–gel glass containing Al3+

Analysis of glasses containing Eu and Tb dopants yields new insights about the role of Al3+ co-doping in improving fluorescence yield of glasses containing rare earth (RE) dopants. Our work suggests that Al co-doping enhances fluorescence by two important mechanisms. (1) At low Al:RE ratio the site symmetry is lowered, allowing more admixture of opposite parity wavefunctions and increased transition probability. (2) At high Al:RE ratio, the highest frequency phonons are of lower energy; so nonradiative decay rates are reduced. In addition, a new technique – post-annealing immersion – is introduced, which allows the study of RE location in the sol–gel matrix. Al co-doping is observed to increase the tendency for RE ions to reside on pore surfaces.