Zhai Hai-Fa,Li Wan,Zhang Jie,Xing Dou-Dou,He Yi-Xiao,Zhang Pan-Pan,Liu Hai-Rui,Yang Ji-En,Wang Bo
Polyhedral CaMoO 4 microcrystallites with excitation-induced tunable luminescent characteristics were successfully synthesized by a hydrothermal method. Polyhedral morphologies with different shapes and exposed facets were observed for the samples prepared at different temperatures. Sharp-vertex polyhedron was obtained at 140 °C due to the increase of (001) surface energy and the sample exhibited the strongest PL emission intensity due to its regular polyhedron morphology. Green and blue light emissions were observed separately under different excitation wavelengths in single CaMoO 4 microcrystallites, which can be attributed to the charge transfer transitions within the [MoO 4 ] 2− complex and the shallow defects in the bandgap, respectively. The excitation-induced tunable luminescent characteristics make it to be a promising inorganic single-emitting component for optical applications.
Molybdate crystals tend to precipitate in nuclear waste glasses, significantly compromising their chemical and thermal stability, thereby rendering them unsuitable for long-term storage. However, the mechanisms by which glass composition influences the precipitation of molybdate crystals remain poorly understood. This study investigated this influence by preparing three series of molybdenum-doped sodium–calcium mixed aluminum borosilicate glasses using the melt-quenching technique. Solid-state nuclear magnetic resonance (SSNMR) spectroscopy, supplemented by Raman spectroscopy, was utilized to examine the glass structure at the atomic scale to reveal composition-dependent structural impacts on crystallization, while transmission electron microscopy (TEM) and X-ray diffraction (XRD) were employed to identify the precipitated crystals. The results demonstrate that increasing the Al2O3 content effectively suppresses molybdate crystal precipitation. It has been proven that high-valence cations differ in their ability to capture free oxygen, with the order of strength being Al3+ > Mo6+ > B3+ and Si4+. It is the strong ability of Al3+ to capture free oxygen and the formation of Al[4]–Ca2+–Mo[6] linkages that are responsible for inhibiting molybdate crystallization in the glass. An intriguing and important abnormal crystallization behavior was observed: a slight substitution of Na2O with CaO resulted in CaMO4 crystal precipitation, whereas larger substitutions paradoxically suppressed it. The findings reveal that in CaO–Na2O mixed aluminum borosilicate glasses, Al[4] preferentially attracts Na+ over Ca2+ to compensate for its negative charge. Meanwhile, Ca2+ ions are capable of forming an Al[4]–Ca2+–Mo[6] linkage, which Na+ ions cannot achieve. This fundamental difference results in the abnormal precipitation of CaMO4 crystals.
Radiative cooling can make the selective emitter cool below ambient temperature without any external energy. Recent advances in photonic crystal and metamaterial technology made a high-efficiency selective emitter achievable by precisely controlling the emitter’s Infrared emission spectrum. However, the high cost of the photonic crystals and meta-materials limit their application. Herein, an efficient bilayer selective emitter is prepared based on the molecular vibrations of functional nanoparticles. By optimizing the volume fraction of the functional nanoparticles, the bilayer selective emitter can theoretically cool 36.7 °C and 25.5 °C below the ambient temperature in the nighttime and daytime, respectively. Such an efficient cooling performance is comparable with the published photonic crystal and metamaterial selective emitters. The rooftop measurements show that the bilayer selective emitter is effective in the ambient air even under direct sunlight. The relatively low cost and excellent cooling performance enable the bilayer selective emitter to have great potential for a practical purpose.Keywords:radiative cooling;bilayer selective emitters;thermal radiation;functional thin films
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