A new double perovskite CaY0.5Ta0.5O3:Mn4+ deep-red phosphor: Synthesis, optical properties, and potential applications in plant-growth LEDs

Highlights:• The best reaction temperature and optimum concentration of Mn⁴⁺ ions in CaY_0.5Ta_0.5O₃ compound were found.• The phosphor emits bright red light excited by 309 nm.• The phosphor exhibits high color purity, and the red LEDs exhibit low correlated color temperature.• The main mechanism of energy transfer was identified. -- Abstract: Deep-red emitting CaY_0.5Ta_0.5O₃:Mn⁴⁺ phosphors were obtained by optimizing the reaction temperature. The structure of CaY_0.5Ta_0.5O₃:Mn⁴⁺ consisted of a double perovskite with the Pnma (62) space group. The luminescence intensity of the synthesized CaY_0.5Ta_0.5O₃:0.3%Mn⁴⁺ at 1550 °C was twice as strong as that at 1500 °C. The photoluminescence spectra of the synthesized CaY_0.5Ta_0.5O₃:Mn⁴⁺ phosphor exhibited a deep-red broadband luminescence from 650 nm to 750 nm with a 680 nm dominated peak due to the ²E_g→⁴A_2g transition of Mn⁴⁺ in TaO₆ octahedral structures. The optimal concentration for the CaY_0.5Ta_0.5O₃:xMn⁴⁺ phosphor was 0.3 mol.%. The concentration quenching effect was ascribed to the dipole–quadrupole interaction. The decay time (0.398–0.171 ms) indicated that the forbidden character of 3d transitions existed among Mn⁴⁺. The crystal field strength and the Racah parameters were discussed to estimate the nephelauxetic effect of Mn⁴⁺ in the CaY_0.5Ta_0.5O₃ host. Besides, the red light-emitting diodes (LEDs) were packaged using the CaY_0.5Ta_0.5O₃:0.3%Mn⁴⁺ phosphor and a 368 nm near-ultraviolet chip. The emission spectrum of the red LED overlapped with the absorption curves of chlorophylls a and b. Results indicated that the CaY_0.5Ta_0.5O₃:Mn⁴⁺ can serve as a component of the deep-red light in plant-growth LEDs.