Mechanisms of fluorescence enhancement in rare earth sol–gel glass containing Al 3

Analysis of glasses containing Eu and Tb dopants yields new insights about the role of Al 3+ 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. ► Al 3+ enhances RE fluorescence in sol–gel glasses through several mechanisms. ► At low Al 3+ concentration RE local site symmetry is modified. ► At high Al 3+ concentration coupling to phonon modes is reduced. ► Al 3+ co-doping increases RE tendency to reside on pore surfaces.