Effect of phase transition on optical and photoluminescence properties of nano-MgWO₄ phosphor prepared by a gamma-ray irradiation assisted polyacrylamide gel method

This study demonstrates the synthesis of the MgWO₄ nanoparticles by a gamma-ray irradiation assisted polyacrylamide gel method through using the citric acid as chelating agent and H₂WO₄ and Mg(NO₃)₂·6H₂O as starting materials. The anorthic MgWO₄ phase can be prepared at a sintering temperature of 600 °C. As the calcination temperature is above 800 °C, a mixed phase including anorthic and monoclinic MgWO₄ phases are observed. The prepared MgWO₄ particles are almost spherical and the particle size increases with the increasing of sintering temperature. The optical and photoluminescence properties of the MgWO₄ nanoparticles change appears to be strongly dependent on the calcining temperature and phase transition. The photoluminescence spectra show that a major emission band around 430 nm is observed when the excitation wavelength is 340 nm of the MgWO₄ xerogel powders calcined at below 600 °C. The intensity of emission peak at 430 nm decreases with the decreasing of sintering temperature. In addition, a major emission band around 468 nm is observed when the excitation wavelength is 280 nm of the MgWO₄ xerogel powders calcined at above 700 °C. The intensity of emission peak at 468 nm increases with the increasing of sintering temperature. The result confirmed that the anorthic MgWO₄ no luminous for the first time. The photofluorescence enhancement of MgWO₄ nanoparticles can be attributed to the type-I band alignment.