High quantum yield red-emission phosphor Li2Ge4O9:Mn4+ for WLEDs application

Abstract

A series of high quantum yield Li2Ge4O9:Mn4+ phosphors are prepared by solid-state reaction method, and their structure has been determined by X-ray powder diffraction with Rietveld refinement. The excitation spectra of Li2Ge4O9:Mn4+ exhibits two excitation bands at 300–400 nm and 400–500 nm corresponding to 4A2→4T1 and 4A2→4T2 transition of Mn4+ ions respectively, and emission spectra from 625 to 750 nm with the strongest emission peak at 671 nm owing to the 4E→4A2 transition of Mn4+ ions. The optimal Mn4+ doping concentrations of Li2Ge4O9 host are determined to be 0.3 mol% and the optimum synthesis temperature is found 800 °C. The Li2Ge4O9:Mn4+ phosphor demonstrated high quantum yield. The as-prepared phosphor shows excellent water-resistance and thermal stability property compared with commercial used K2SiF6:Mn4+ phosphor. Finally, a white LED with improved Ra (from 72.5 to 82) and reduced Tc (from 6530 K to 6107 K) was fabricated by using a 450 nm blue chip with Y3Al5O12:Ce3+ and the as-prepared Li2Ge4O9:0.003Mn4+ phosphor.