A deep red phosphor Li2MgTiO4:Mn4+ exhibiting abnormal emission: Potential application as color converter for warm w LEDs
Abstract The exploration of new red phosphor based on rare earth free ion activated oxide is of great practical value in the field of phosphors converted white light emitting diode (w LED) lightings. Here, we report on a novel Mn4+ doped Li2MgTiO4 phosphor prepared by a solid state reaction route, matching with the blue chips and showing strong deep red emission with an abnormal broad band centered at ~676 nm. The crystal structure of Li2MgTiO4 is identified and investigated by Rietveld refinement. The crystal field strength (Dq) and the Racah parameters (B and C) are estimated to evaluate the nephelauxetic effect of Mn4+ suffered in Li2MgTiO4 host lattice. The calculated results well conform to show linear dependence of E(2Eg) on b1 parameter which may provide an indication of the Mn4+emission position on the basis of b1. The photoluminescence properties are investigated systematically with the aid of diffuse reflection spectra, steady and transient state fluorescence measurements at high, low and room temperature. Concentration quenching and thermal quenching are elucidated in detail. As proof of concept, the as prepared Li2MgTiO4:Mn and commercial YAG:Ce phosphors are applied to the package of a blue LED chip to fabricate a warm w LED.