Synthesis and improved photoluminescence of hexagonal crystals of Li 2 ZrF 6 :Mn 4+ for warm WLED application.

A series of red-emitting phosphors composed of Li2ZrF6:Mn4+ (LZF:Mn) have been synthesized via an ionic-exchange reaction route at room temperature. The microstructure and optical characterizations have been investigated according to the detailed experiments. The morphology of the phosphor LZF:Mn changes with the concentration of HF, the reaction time and temperature. The uniform crystals of LZF:Mn with regular hexagonal tablets have been obtained in 30-40 wt% HF solutions by conducting the reaction at room temperature for about 8 h. The influences of reaction parameters on the morphology and photoluminescence properties of LZF:Mn have been systematically investigated. The luminescence intensity of LZF:Mn has been optimized by controlling the synthesis procedure and parameters. The white light-emitting diode (WLED) fabricated with LZF:Mn and Y3Al5O12:Ce3+ (YAG:Ce) on InGaN LED chip displays a warm white light with correlated color temperature (CCT) at 3789.4 K and color rendering index (CRI) of 91.