ZnAl₂O₄:Eu³⁺ Nanoparticle Phosphors Co-doped with Li⁺ for Red Light-Emitting Diodes

In recent years, rare-earth doped phosphors have gathered immense attention in the luminescence field for lighting and electronic display applications. However, the unavailability of an efficient and low-cost red phosphor is a major challenge for the widespread deployment of white light-emitting diodes (WLEDs) for practical purposes. Here we report red light-emitting Li+ co-doped ZnAl2O4:Eu3+ nanophosphors synthesized by a modified sol–gel route. These nanophosphors show excellent red emission due to the 5D0 → 7Fj (j = 1, 2, 3, and 4) transition of Eu3+ ions under 394 nm excitation. Li+ co-doped ZnAl2O4:Eu3+ nanophosphors exhibit an almost 2-fold increase in photoluminescence (PL) intensity upon incorporation of the optimum amount of Li+ in the ZnAl2O4:Eu3+ matrix. Apart from that, Li+ co-doping leads to the improvement of CIE coordinates that is also reflected from the enhanced color purity offered by the co-doped nanophosphors. Steady-state as well as time-resolved PL spectra clearly reveal that addition of Li+ co-activator successfully reduces nonradiative transitions in the co-doped nanophosphors. Introduction of Li+ in Eu3+ doped ZnAl2O4 effectively neutralizes the charge imbalance problem and thus leads to a significant increase in the PL efficiency of the nanophosphors. The red LED fabricated by those co-doped nanophosphors exhibits strong red emission under a driving voltage of 3 V. Obtained results strongly highlight the bright prospect of Li+ co-doped ZnAl2O4:Eu3+ nanophosphors in the LED and display applications.