## Abstract

Systematic studies of cooperative upconversion and ${\mathrm{Yb}}^{3+}\u2013{\mathrm{Er}}^{3+}$ energy transfer in newly developed phosphate glasses were performed by a rate-equation formalism. The cooperative-upconversion coefficients of the ${}^{4}{I}_{13/2}$ level for different ${\mathrm{Er}}^{3+}$ concentrations were determined from the luminescence-decay curves for high pump intensities. A small cooperative-upconversion coefficient of $1.1\times {10}^{-18}{\mathrm{cm}}^{3}/\mathrm{s}$ was obtained for a high ${\mathrm{Er}}^{3+}$ concentration of $4\times {10}^{20}\hspace{0.5em}\mathrm{ions}/{\mathrm{cm}}^{3}.$ ${\mathrm{Yb}}^{3+}\u2013{\mathrm{Er}}^{3+}$ energy-transfer coefficients for an ${\mathrm{Er}}^{3+}$ concentration of $2\times {10}^{20}\hspace{0.5em}\mathrm{ions}/{\mathrm{cm}}^{3}$ codoped with different ${\mathrm{Yb}}^{3+}$ concentrations were calculated from the lifetime measurements of the ${}^{2}{F}_{5/2}$ level of ${\mathrm{Yb}}^{3+}\hspace{0.5em}\mathrm{ions}.$ For ${\mathrm{Er}}^{3+}$ codoped with an ${\mathrm{Yb}}^{3+}$ concentration of $6\times {10}^{20}\hspace{0.5em}\mathrm{ions}/{\mathrm{cm}}^{3},$ an energy-transfer coefficient of $1.1\times {10}^{-16}{\mathrm{cm}}^{3}/\mathrm{s}$ and an energy-transfer efficiency higher than 95% were determined from our measurements under weak excitation. The cooperative-upconversion coefficients of ${\mathrm{Yb}}^{3+}\u2013{\mathrm{Er}}^{3+}$-doped samples were found to be consistent with that of an ${\mathrm{Er}}^{3+}$-doped sample with the same ${\mathrm{Er}}^{3+}$ concentration. The weak cooperative-upconversion effect of high ${\mathrm{Er}}^{3+}$ concentrations and efficient ${\mathrm{Yb}}^{3+}\u2013{\mathrm{Er}}^{3+}$ energy transfer indicate that these newly developed ${\mathrm{Er}}^{3+}$- and ${\mathrm{Yb}}^{3+}\u2013{\mathrm{Er}}^{3+}$-doped phosphate glasses are excellent for active device applications.

© 2000 Optical Society of America

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