Ultralow-threshold wideband-tunable single-mode ultraviolet lasing from lanthanide-doped upconversion nanomaterials

Ultraviolet (UV) lasers with dynamic wavelength-tunability and high monochromaticity are crucial in a multitude of practical applications yet still remarkable challenges. Here, we show wide wavelength-tuning of single-mode UV lasing based on lanthanide-doped upconversion nanoparticles (UCNPs). The rationally designed Yb³⁺/Er³⁺/Tm³⁺/Gd³⁺/Ce³⁺ co-doped multilayer UCNPs, which exhibits a broad gain spectrum with the full width of half maximum of around 57 nm in the UV regime, are developed. More importantly, by taking advantages of a diffraction grating as the tuning component, stable single-mode emission can be achieved in the UCNPs-based external-cavity-extended Fabry–Pérot laser at room temperature. Specifically, the lasing threshold is around 137 µJ cm^–2, which is two orders of magnitude lower than that in the previously reported articles. Precise wavelength-tuning from 310 to 363 nm can be realized by adjusting the Littrow angle. This achievement highlights a portable alternative to continuously wideband-tunable UV lasers and opens up new opportunities for constructing compact solid-state UV photon sources.