Abstract
It is a daunting challenge to realize ultraviolet C (UVC) lasing (i.e., has a wavelength range from 200 to 275 nm) from upconversion nanocrystals due to their low upconversion efficiency. Here, we fabricate ${\rm{B}}{{\rm{a}}_2}{\rm{La}}{{\rm{F}}_7}{:}{\rm{Y}}{{\rm{b}}^{3 +}}({{90}}\;{\rm{mol}}\%)$, ${\rm{T}}{{\rm{m}}^{3 +}}({{5}}\;{\rm{mol}}\%)$ upconversion nanocrystals from amorphous borosilicate glass to support emission at ${\sim}{{263}}\;{\rm{nm}}$ under 980 nm ns laser excitation. The excitation threshold can be further reduced from ${\sim}{{130}}$ to ${\sim}{26.5}\;{\rm{mJ/c}}{{\rm{m}}^2}$ by using a cylindrical microcavity. We also found that the growth of defect-free ${\rm{B}}{{\rm{a}}_2}{\rm{La}}{{\rm{F}}_7}$ nanocrystals with a high concentration of codoping ${\rm{Y}}{{\rm{b}}^{3 +}}$ and ${\rm{T}}{{\rm{m}}^{3 +}}$ ions inside high optical damage threshold borosilicate glass is the key to achieving room-temperature UVC upconversion lasing under high-intensity excitation.
© 2020 Optical Society of America
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