Formation of zinc silicate in supercritical water followed with in situ synchrotron radiation X-ray diffraction

Phase formation mechanism of a highly practical inorganic phosphor, α-Zn 2SiO 4:Mn 2+ crystal in supercritical water firstly has been investigated in situ with synchrotron radiation X-ray diffraction. Green-emitting α-Zn 2SiO 4:Mn 2+ crystal formed at a reaction time as low as 400 s at temperatures close to the critical point of water (374 °C) and at high-pressures of around 0.7 GPa compared with typical conditions ( ca. 1200 °C, 4 h) for conventional solid-state processes. The operating temperatures and pressures are close to industrial conditions for hydrothermal growth of single crystals, suggesting that supercritical water conditions can be used as a low environmental burden method for producing inorganic phosphors. In this study, it was confirmed that the hydrate mineral, hemimorphite (Zn 4(OH) 2Si 2O 7·H 2O) appears with the anhydrous mineral, willemite (α-Zn 2SiO 4) in supercritical water.