CaF₂‑Based Near-Infrared Photocatalyst Using the Multifunctional CaTiO₃ Precursors as the Calcium Source

Multistage formation of fluoride upconversion agents from the related-semiconductor precursors provides a promising route for the fabrication of near-infrared (NIR) photocatalysts with high photocatalytic activities. Herein, the cotton templated CaTiO₃ “semiconduction” precursors (C-CaTiO₃) were used to synthesize the NIR photocatalyst of Er³⁺/Tm³⁺/Yb³⁺–(CaTiO₃/CaF₂/TiO₂) (C-ETYCCT), and the functions of the Ca²⁺ source for CaF₂ and the heterostructure formations were displayed by C-CaTiO₃. The generated CaF₂ acted as the host material for the lanthanide ions, and the heterostructures were constructed among anatase, rutile, and the remaining CaTiO₃. The induced oxygen vacancies and Ti³⁺ ions enabled the samples to utilize most of the upconversion luminescence for photocatalysis. The NIR driven degradation rate of methyl orange (MO) over C-ETYCCT reached 52.34%, which was 1.6 and 2.5 times higher than those of Er³⁺/Tm³⁺/Yb³⁺–(CaTiO₃/TiO₂) (C-ETYCT) and Er³⁺/Tm³⁺/Yb³⁺–(CaTiO₃/CaF₂) (C-ETYCC), respectively. The degradation rates of MO and salicylic acid over C-ETYCCT with UV–vis–NIR light irradiation were also much higher than those of other samples, which were mainly results of the contributions of its high upconversion luminescence and the efficient electron–hole pair separation

Morphology Evolution and Degradation of CsPbBr₃ Nanocrystals under Blue Light-Emitting Diode Illumination

Under illumination of light-emitting diode (LED) or sunlight, the green color of all-inorganic CsPbBr₃ perovskite nanocrystals (CPB-NCs) often quickly changes to yellow, followed by large photoluminescence (PL) loss. To figure out what is happening on CPB-NCs during the color change process, the morphology, structure, and PL evolutions are systematically investigated by varying the influence factors of illumination, moisture, oxygen, and temperature. We find that the yellow color is mainly originated from the large CPB crystals formed in the illumination process. With maximized isolation of oxygen for the sandwiched film or the uncovered film stored in nitrogen, the color change can be dramatically slowed down whether there is water vapor or not. Under dark condition, the PL emissions are not significantly influenced by the varied relative humidity (RH) levels and temperatures up to 60 °C. Under the precondition of oxygen or air, color change and PL loss become more obvious when increasing the illumination power or RH level, and the large-sized cubic CPB crystals are further evolved into the oval-shaped crystals. We confirm that oxygen is the crucial factor to drive the color change, which has the strong synergistic effect with the illumination and moisture for the degradation of the CPB film. Meanwhile, the surface decomposition and the increased charge trap states occurred in the formed large CPB crystals play important roles for the PL loss