Although widely need from various applications, the luminescence of Cr³⁺ is easily prone to thermal quenching (TQ), causing remarkable intensity reduction as temperature rises, and posing a significant constraint in applications such as high-power lighting, solid-state lasers, and high-temperature optical sensing. Numerous strategies have been reported to realize anti-thermal quenching luminescence (ATQL) of Cr³⁺. However, researches into anti-thermal quenching upconversion luminescence (ATQUL) of Cr³⁺ are barely seen. Herein, taking advantage of the enhanced luminescence of Yb³⁺ facilitated by the Frenkel defects formed within Sc₂(WO₄)₃ (SWO) matrix upon heating, we have established Yb³⁺ $\to$ Cr³⁺ cooperative sensitization pathway for upconversion luminescence of Cr³⁺, and achieved ATQUL of Cr³⁺ in SWO:Yb/Cr. Our findings have not only offered novel perspectives for medium to high-temperature applications of Cr³⁺-based phosphors, the design principles are also extendable to other transition metal ions.

Metasurface significantly enriches the light-matter interaction and promotes the development of planar optics. In recent years, with the rapid advancements of terahertz (THz) technology, THz devices with switchable and reconfigurable functions have been intensively pursued. Liquid crystal (LC), a unique soft matter that combines the fluidity of liquids and the order of crystals, is now indispensable in displays and spatial light modulations. LC is integrated with metasurfaces to realize dynamic THz devices and apparatuses as well. This review summarizes the research progress in LC based THz metadevices in three different respects: LC planar THz devices, LC integrated metal metasurfaces, and LC integrated dielectric metasurfaces. Various technologies for fabrications of LC microstructures and integrations of LCs with metal or dielectric metasurfaces are presented. The obtained LC metadevices exhibit excellent responsiveness to external stimulus such as electric fields, magnetic fields, heat, and light. By this means, the amplitude, frequency, phase as well as polarization of THz waves are dynamically manipulated. The LC based tunable THz metadevices will significantly improve THz applications in imaging, communication, and sensing.