Highly enhanced blue-emission of LnOCl:Tm prepared by dehydration of Ln(OH)2Cl:Tm (Ln = La and Gd)

Tm3+-doped dihydroxychlorides Ln(OH)2Cl:Tm (Ln = La and Gd) have been prepared by the solvothermal reaction. Subsequent thermal dehydration of these hydroxychloride precursors produced the PbFCl-type blue-emitting oxychloride phosphors LnOCl:Tm of different morphologies. The dehydration of La(OH)2Cl:Tm rods results in LaOCl:Tm with highly porous particle surface, which showed a quite low photoemission intensity. The elimination of surface porosity by using a surfactant yields a rhomboidal-shape phosphor particles and significantly enhances the emission intensity of LaOCl:Tm. In contrast, GdOCl:Tm obtained from Gd(OH)2Cl:Tm reveals no porous surface of particles and exhibits the blue-emission about 20 times stronger than that of the same composition directly prepared under the ambient pressure. It is suggested that this indirect synthesis of PbFCl-type oxychloride phosphors from corresponding hydroxychlorides provides a selective route to control the shape and porosity of particles under the solvothermal condition and consequently to increase the photoemission efficiency.