A far-red-emitting ZnAlCrO phosphor for plant growth LED applications.

ZnAlCrO ( = 0 and 0.05) samples were synthesized a high-temperature solid-state reaction method. The structure, photoluminescence properties, EPR measurements, thermal stability, and chromaticity diagram of the far-red phosphor ZnAlCrO were investigated. These measurements have enabled us to study the Cr transitions and the site symmetry of Cr in the ZnAlO host lattice and examine the suitability of ZnAlCrO for plant growth application. According to optical and EPR measurements, Cr ions substitute Al ions with symmetry in the ZnAlO host. PLE measurement indicates that upon excitation at 390 nm and 530 nm, the far-red phosphor ZnAlCrO exhibited bright far-red emission around 687 nm. Photoluminescence phenomena show a sharp R line origin from the sublevels of the E(G) → A(F) transition in Cr ions. The E level was split into E (Ē) and E (2Ā) levels in the distorted crystal field environment, and the sharp R line in the ZnAlO matrix was split into R and R lines. In this paper, the temperature-dependent luminescence characteristics of ZnAlCrO have been investigated. As the temperature increased from 300 K to 440 K, a slight decrease in the intensity of the R1 and R2 lines was observed under excitation at 390 nm. The experimental results show that the ZnAlCrO phosphors exhibit a nearly zero-thermal-quenching behavior. The CIE chromaticity coordinates of the ZnAlCrO phosphor were located at the boundary of the chromaticity diagram, signifying that the phosphors possessed high color purity. The emissions of the ZnAlCrO phosphor match well with the PFR absorption of phytochromes in plants. The investigation indicates that ZnAlCrO is a potential far-red phosphor matching ultraviolet (UV) LED chips for plant growth applications.