Effect of micro-crystallization on near-infrared shielding performance of Li0.09K0.23WO3 doped glass for energy-saving window

Effect of micro-crystallization (based on annealing time and temperature) on near-infrared (NIR)-shielding properties of Li0.09K0.23WO3 doped glass was investigated. The tungsten bronze doped glass was prepared by a facile melt-quenching technique. Structure and optical properties of the glass and glass-ceramics were characterized by X-ray diffraction analysis (XRD), Raman, and UV–Vis–NIR spectrophotometry, respectively. Increasing the annealing temperature increases in the range from 400 °C to 500 °C, the tungsten-functional unit Li0.09K0.23WO3 structure, which is responsible for NIR-shielding, changes the structural state from amorphous state to crystalline state gradually. Thus, the NIR-shielding properties of glass are significantly enhanced. Furthermore, annealing glass samples at 450 °C, during timeframe from 2 h to 8 h, causes crystallization and grain growth of the functional units, thus NIR-shielding property of the glasses is enhancing. It worth to be mentioned, that the increase of annealing temperature and time duration causes excessive grain growth in the glass matrix, which leads to decreasing of the optical transmittance in the visible light wavelength region. We have found, that the glass sample annealing temperature is at 450 °C with treatment time of 6 h yields the best results. In such manner the optical transmittance at λ = 1500 nm wavelength is 16.5 % and the highest transmittance of visible light wavelength region reaches 65 %. We conclude, that the NIR-shielding properties are adjustable and can be tailored by annealing temperature and time duration, which is expected to enhance the design and vary visual aspects of energy-saving windows.