Deep UV random lasing from NaGdF₄:Yb³⁺,Tm³⁺ upconversion nanocrystals in amorphous borosilicate glass

The realization of lanthanide-doped upconversion nanocrystals embedded in a robust and transparent solid medium is highly desired to achieve deep UV (<300nm) lasing. Here, we fabricate NaGdF₄:Yb³⁺,Tm³⁺ upconversion nanocrystals inside amorphous borosilicate glass to support ∼290nm random lasing emission under 980 nm excitation. We found that with careful control of the growth process, which is the key to achieve high-crystallinity nanocrystals, the nanocrystals can suppress defect-related quenching and enhance ¹I₆→³H₆(⁶I_J→⁸S_7/2) transition of Tm³⁺ (Gd³⁺) ions under five-photon absorption excitation so that high optical gain (>45cm^-1) at ∼290nm can be obtained.