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)center dot 6H(2)O as starting materials. The anorthic MgWO4 phase can be prepared at a sintering temperature of 600 degrees C. As the calcination temperature is above 800 degrees 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 degrees 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 degrees 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.