Crystal Growth and Color Tuning of Large Mn(PO₃OH)·3H₂O Crystals via an Evaporation-Assisted Aqueous Route at Room Temperature

Large Mn(PO₃OH)·3H₂O crystals have been prepared from aqueous solutions containing MnCl₂ and (NH₄)₂HPO₄ by an evaporation-induced crystal growth technique. The slow solvent evaporation at room temperature maintained the supersaturation of the precursor solution for a long time, resulting in the continuous growth of Mn(PO₃OH)·3H₂O crystals. The addition of citric acid as a chelating agent and increasing the total volume of the precursor solutions helped to maintain the mild supersaturation conditions for a longer time period, and transparent, unbranched Mn(PO₃OH)·3H₂O crystals above 2 mm in size were produced by aging for 8 weeks. The large Mn(PO₃OH)·3H₂O single crystals exhibited a pink color, and the color became stronger by doping with Co²⁺ ions.