Intense Near-UV Upconversion Luminescence in ${\rm Tm}^{3+}/{\rm Yb}^{3+}$ Co-Doped Low-Phonon-Energy Lithium Gallogermanate Oxide Glass

Intense near-ultraviolet (UV) upconversion emission of 365 nm has been obtained in Tm³⁺/Yb³⁺ co-doped lithium gallogermanate oxide glass upon a 980-nm laser diode excitation. This near-UV emission originates from the Tm³⁺:¹D₂→³H₆ transition. The cross relaxation process [¹G₄,³H₄]→[³F₄,¹D₂] is shown to play a critical role in population of the emitting level Tm³⁺¹D₂. The low phonon energy (~ 825 cm^-1) and high transparency at near-UV of the glass matrix also contribute to this emission. The emission cross section is calculated to be 6.46×10^-21cm², which is larger than Tm³⁺1.47 and 1.80-μm transitions. The results indicate that, other than single crystal and nano-glass-ceramic, this system is a promising alternative for development of near-UV lasers.