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-Zn2SiO4:Mn2+ crystal in supercritical water firstly has been investigated in situ with synchrotron radiation X-ray diffraction. Green-emitting α-Zn2SiO4:Mn2+ 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 (Zn4(OH)2Si2O7·H2O) appears with the anhydrous mineral, willemite (α-Zn2SiO4) in supercritical water.