Broadband downconversion from oxygen-deficient centers to Yb^3+ in germanate glasses

We report broadband downconversion from ultraviolet to near-infrared in ${\mathrm{Yb}}^{3+}$-doped oxygen-deficient $\mathrm{Sr}\mathrm{O}–{\mathrm{Al}}_2{\mathrm{O}}_3–\mathrm{Ge}{\mathrm{O}}_2$ glasses. Oxygen-deficient centers are introduced in germanate glasses by adding metal Al instead of corresponding oxide $\left({\mathrm{Al}}_2{\mathrm{O}}_3\right)$. Tunable luminescence related to these defects is observed. Conversion of broadband ultraviolet light to blue-green tunable luminescence and to near-infrared emission is detected in glasses. The energy transfer efficiency increases with increasing ${\mathrm{Yb}}_2{\mathrm{O}}_3$ concentration. The dependence of energy transfer efficiency on wavelength is also discussed.