Although upconversion rare-earth (RE) materials have excellent luminescence properties, the luminescence intensity and thermal stability of phosphors are not favorable due to RE doping induced vacancies. This work focused on enhancing luminescence intensity and stability of phosphor by charge compensation and three-dimensional (3D) printing. The luminescence results showed that Ca_0.697Yb_0.2Er_0.0015Tm_0.0005F₂ with charge compensation exhibited luminescence intensity 3.2 times higher than that of Ca_0.798Yb_0.2Er_0.0015Tm_0.0005F₂ non-charge compensation. The luminescence of resin-coated luminescent materials is still stable after 6 months. The constructed white light-emitting diodes (WLEDs) also exhibit consistent and outstanding color rendering characteristics, with a color rendering index (CRI) of up to 81 and a low color temperature (CCT).

Heterojunction catalysts have been demonstrated to significantly enhance photocatalytic CO₂ reduction activity. However, the direction and rate of charge transfer at the catalyst interfaces remain the primary limiting factors for catalytic performance. In this study, a ternary heterojunction MgTi₂O₅ (MT)/TiO₂/g-C₃N₄ (CN) was prepared via in situ composite synthesis, and rare earth single-atom Ho, with abundant 4f electron energy levels, was utilized as an electron transfer channel within the heterojunction. This approach effectively facilitated electron transfer at the catalyst interface, and its photocatalytic activity and mechanism were thoroughly investigated. Remarkably, the catalyst exhibited distinct charge transport mechanisms under visible light and ultraviolet light. In the absence of a sacrificial agent, the sample MT:CN-1 demonstrated optimal performance under visible light, achieving a CO yield of 31.42 μmol·g⁻¹·h⁻¹, which is 9.8 times higher than that of pristine CN. Under ultraviolet light, the sample MT:CN-2 exhibited the best performance, with a CO yield of 40.61 μmol·g⁻¹·h⁻¹, representing a 4.2-fold enhancement compared to CN. Furthermore, the charge transfer mechanism of the catalyst was elucidated using in situ X-ray photoelectron spectroscopy (XPS) and femtosecond transient fluorescence spectroscopy techniques.