Rare-earth free far-red emitting perovskite phosphor NaYBa₄W₂O₁₂:Mn⁴⁺ for indoor plant cultivation lighting

A series of rare-earth free far-red emitting phosphor NaYBa4W2O12: xMn(4+) ( <= x <= 0.75%, NYBW: Mn4+) is successfully synthesized for application in near-ultraviolet (n-UV) light pumped plant cultivation light-emitting diodes (LEDs). The phase purity, crystal structure, electronic structure and luminescent properties of NYBW: Mn4+ are investigated in detail. The results indicate that all NYBW: Mn4+ phosphors are well crystallized with a direct band gap of 3.86 eV. Broad excitation band can be found with dominant wavelengths at 365 and 520 nm, indicating NYBW: Mn4+ can be efficiently excited by commercial n-UV or green LED chip. Upon 360 nm excitation, NYBW: Mn4+ shows intense broad-band far-red emission centered at 696 nm, attributed to the E-2(g)->(4)A(2g) transition of Mn4+. The optimal doping concentration of Mn4+ is determined to be 0.1% and the concentration quenching mechanism is the dipole-quadrupole interaction. The decay time decreases from 0.58 to 0.081 ms with Mn4+ concentration increasing from 0.025 to 0.75%. The temperature quenching behaviour of Mn4+ in NYBW is investigated, with a thermal activation energy estimated to be about 0.375 eV. Finally, a far-red emitting LED device is fabricated by coating NYBW: Mn4+ phosphor on a 365 nm n-UV LED chip. The above results guarantee that the as-prepared far-red emitting phosphor NYBW: Mn4+ has great potential for application in indoor plant cultivation LEDs.