Role of crystal water in luminescence properties of copper-doped hydronium alunite

Abstract

Copper-doped hydronium alunite [(H₃O)Al₃(SO₄)₂(OH)₆:Cu], a novel luminescent sulfate material, exhibiting blue luminescence was successfully synthesized under hydrothermal conditions. The originality of this luminescent material is such that the host crystal structure consists of crystal water (hydronium ions and hydroxyl radicals). Herein, we reported the results of a detailed investigation of changes in luminescence characteristics of the material with heat treatments. It was found that the material’s emission intensity was significantly reduced by heat treatment at temperatures ≥318 °C. The effect of varying amounts of copper and the extent of dehydration on the emission intensity was also investigated. As a result, a clear tendency was obtained that the luminescence intensity decreased as the weight loss increased due to dehydration. Thus, the presence of copper and crystal water are important factors affecting the luminescence of the material.