Simple charge compensation for superb red light emission enhancement

In recent years, Mn⁴⁺doped oxide phosphors have attracted extensive attention in the field of indoor plant light supplementation due to their red emission. In this study, a rare earth-free red phosphor, Li₃Mg₂NbO₆(LMN):Mn⁴⁺, was prepared by high-temperature solid-state reaction. The resultant phosphor exhibited red emission within the 600–800 nm band, with a peak at 668 nm, when excited by 351 nm and 468 nm. DFT calculations of charge density and formation energies determined that Mn⁴⁺tends to occupy the Mg²⁺sites, leading to a charge imbalance that affects the luminescence intensity of the material. In light of the foregoing, charge compensation strategy was adopted in order to achieve charge balance through excessive doping of Li⁺, Na⁺and K⁺alkali metal ions. The optimal doping concentrations of Li⁺, Na⁺and K⁺were determined to be 0.35, 0.4 and 0.3, respectively. The luminescence intensity of LMN:Mn⁴⁺phosphors was found to increase to 453%, 500% and 708% of the initial intensity. Concurrently, the quantum efficiency (QE) of the phosphor LMN:Mn⁴⁺was enhanced from 33.8 % to 48.1%, 57.04% and 69.19%, respectively, by means of additional doping with Li⁺, Na⁺and K⁺. At 100 °C, the emission intensity of the LMN:0.01Mn⁴⁺phosphor was found to be 73.6% of that at room temperature (25 °C). The thermal stability of additional Li⁺, Na⁺and K⁺by charge-compensated doping is slightly reduced. Finally, LMN:0.01Mn⁴⁺, 0.3K₂CO₃ phosphor and a blue light chip were used to prepare the phosphor conversion light-emitting diodes (pc-LEDs). The electroluminescence spectra of the pc-LEDs exhibited a blue and red double emission, corresponding to the absorption bands of chlorophyll B and photochrome P_R. This finding indicates that pc-LEDs have considerable potential for application in the field of plant growth LED lamps.