The evolution and role of NH₄Cl flux used to synthesize double perovskite BaLaMgSbO₆: a potential red phosphor for white LEDs

Eu³⁺ ions activated BaLaMgSbO₆ phosphors were successfully synthesized by the solid-state reaction method using NH₄Cl as the flux. The BaCl₂ was selected to substitute BaCO₃ as the starting material to attest that NH₄Cl not only reacted with BaCO₃ but also reacted with other starting materials. The analysis of TG/DSC was used to probe the role of NH₄Cl flux in the process of synthesizing BaLaMgSbO₆ powders. The crystal structure was investigated by XRD and Rietveld refinement, and the morphology by SEM. The phosphors had monoclinic double perovskite structure with the space group P21, as well as the rock-salt ordering of B-site. The luminescence properties, including the photoluminescence excitation and emission spectra, and the color coordinates were investigated. Also, the relationship between the crystalline size and the emission intensity were discussed. With increasing the calcination temperature, both the crystalline size and the emission intensity monotonously increased. The relative intensity ratio of red/orange emission was used to measure the degree of distortion from the inversion symmetry of the local environment of the Eu³⁺ ions in BaLaMgSbO₆.