Novel double-perovskite SrLaLiTeO6:Mn4+ far-red phosphor with superior thermal stability for indoor plant growth LED

Highlights: • Red-emitting Mn⁴⁺ activated double perovskite SrLaLiTeO₆ phosphors were firstly prepared. • The bandgap and electronic structures of the SrLaLiTeO₆ host were investigated. • SrLaLiTeO₆: Mn⁴⁺ phosphors presented far red light peaking at 696 nm and 708 nm under different excitations. • The nephelauxetic effect of Mn⁴⁺ in the SrLaLiTeO₆ host were estimated. • A red-LEDs device for indoor plant cultivation was made. A series of red-emitting phosphors SrLaLiTe_1-xO₆: xMn⁴⁺ were prepared via high-temperature solid-state reaction technique. The structure of SrLaLiTeO₆ (abbreviated as SLLT) is a typical cubic double-perovskite structure with the space group of Fm-3m (225). Based on the density functional theory (DFT) calculation, the SrLaLiTeO₆ presents a direct band gap property with the band gap energy (E_g) of 3.22eV. The estimated E_g of SrLaLiTeO₆ and SrLaLiTe_0.988O₆: 0.012Mn⁴⁺ were evaluated to be 3.08 eV and 2.98 eV derived from diffuse reflectance spectra, respectively. The emission spectra show a narrow emission band from 650 nm (15384 cm⁻¹) to 770 nm (12987 cm⁻¹) peaking at 696 nm and 708 nm, which exhibits a greater overlap with the phytochrome (P_R and P_FR) absorption. Furthermore, the nephelauxetic effect of Mn⁴⁺ in the SLLT host were estimated in detail by using the crystal field strength (Dq) and Racah parameters (B, C). Finally, the intensity remained at 79.01% and 81.44% of the original intensity when the temperature was elevated at 423 K, respectively, which illustrates good thermal stability. All these results manifest that SrLaLiTeO₆: Mn⁴⁺ is expected to be a candidate for indoor plant cultivation LED.