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 Tm
³⁺
/Yb
³⁺
co-doped lithium gallogermanate oxide glass upon a 980-nm laser diode excitation. This near-UV emission originates from the Tm
³⁺
:
¹
D
₂
→
³
H
₆
transition. The cross relaxation process [
¹
G
₄
,
³
H
₄
]→[
³
F
₄
,
¹
D
₂
] is shown to play a critical role in population of the emitting level Tm
³⁺¹
D
₂
. 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
^-21
cm
²
, which is larger than Tm
³⁺
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.