Crystal Growth and Color Tuning of Large Mn(PO<sub>3</sub>OH)·3H<sub>2</sub>O Crystals via an Evaporation-Assisted\nAqueous Route at Room Temperature

Large\nMn(PO<sub>3</sub>OH)·3H<sub>2</sub>O crystals have been\nprepared from aqueous solutions containing MnCl<sub>2</sub> and (NH<sub>4</sub>)<sub>2</sub>HPO<sub>4</sub> by an evaporation-induced crystal\ngrowth technique. The slow solvent evaporation at room temperature\nmaintained the supersaturation of the precursor solution for a long\ntime, resulting in the continuous growth of Mn(PO<sub>3</sub>OH)·3H<sub>2</sub>O crystals. The addition of citric acid as a chelating agent\nand increasing the total volume of the precursor solutions helped\nto maintain the mild supersaturation conditions for a longer time\nperiod, and transparent, unbranched Mn(PO<sub>3</sub>OH)·3H<sub>2</sub>O crystals above 2 mm in size were produced by aging for 8\nweeks. The large Mn(PO<sub>3</sub>OH)·3H<sub>2</sub>O single\ncrystals exhibited a pink color, and the color became stronger by\ndoping with Co<sup>2+</sup> ions.