Mechanisms of Li+Ions in the Emission Enhancement of KMg4(PO4)3:Eu2+for White Light Emitting Diodes

Codoping with Li⁺ is a prevalent strategy to improve the optical efficiency of luminescent materials, while the mechanisms of enhancement are still ambiguous. Herein, we delineate the major ways by which Li⁺ enhanced the emission of orthophosphate phosphor KMg₄(PO₄)₃:Eu²⁺ and quantify the relative contributions of each mechanism. Results from X-ray diffraction, scanning electron microscopy, and steady-state and time-resolved fluorescence spectroscopies show that the 3.8-fold increase in emission intensity caused by optimized Li⁺ doping was attributed to flux effect (∼30.84%), crystal-field splitting (∼5.30%), and a reduction in concentration quenching (∼63.86%), respectively. The as-synthesized materials also show excellent thermal stability and an increased internal quantum efficiency of 84.02% compared with 53.13% of nondoped phosphors. The white light emitting diodes employing KMg₄(PO₄)₃:Eu²⁺,Li⁺ as a blue-emitting component exhibit superior electroluminescence properties. The above results demonstrate that introducing Li⁺ ions can obviously enhance the luminescence efficiency of KMg₄(PO₄)₃:Eu²⁺ phosphor.