A high-efficiency double perovskite phosphor SrLaNaTeO6:Mn4+: Potential applications in w-LEDs and indoor plant growth lighting

A novel deep-red phosphor with Mn4+-doped double perovskites SrLaNaTeO6 (SLNTO) was synthesized by the conventional high-temperature solid-state method. SLNTO contains both [NaO6] and [TeO6] octahedra. The octahedral structure of double perovskites facilitates the doping of Mn4+. The band gap (Eg) of the direct semiconductor SLNTO is 2.88 eV. With an excitation wavelength of 322 nm, SLNTO:Mn4+ has a 700 nm deep-red wavelength emission assigned to the energy level transition from 2E1g to 4A2g of Mn4+ ions. Photoluminescence (PL) of the sample and phytochrome far-red light (PFR) absorption are satisfactory matches. According to the Tanabe-Sugano diagram, Mn4+ is located in the strong crystalline field for 2E1g. A 2.0 mol% concentration of Mn4+ is optimal; further high doping results in concentration quenching, ascribed to the neighbour ion interaction and dipole-dipole (d-d) interactions. The internal quantum efficiency (IQE) is 87.84 %. Additionally, the electroluminescent (EL) spectrum of the encapsulated plant growth lamp overlaps with the chlorophyll a and b absorption spectra. Its Commission Internationale de l'Eclairage (CIE) coordinates of SLNTO:2.0 mol%Mn4+ phosphor with a near-ultraviolet (n-UV) chip are located in (0.720, 0.280). The phosphor-converted white lightemitting diode (pc-WLED) has a high colour rendering index (Ra = 96) with a suitable correlated colour temperature (CCT = 6240 K). The results are satisfactory for white light-emitting diodes (w-LEDs) and plant growth lamps.