Novel polygonal structure Mn4+ activated In3+-based Elpasolite-type hexafluorides red phosphor for warm white light-emitting diodes (WLEDs)

Abstract

A novel type polygonal structure red emission Elpasolite-type hexafluorides (NH₄)₂NaInF₆:Mn⁴⁺ phosphor is successfully synthesized by hydrothermal and coprecipitation methods. The samples exhibit two typical absorption bands located at the ultraviolet-visible (369 nm) and the blue light area (470 nm) and emit bright red light centered at 633 nm with high color purity. Powder X-ray diffraction (XRD) has been used to demonstrate the phase purity and crystal structure of the samples synthesized. The corresponding surface morphology and composition have been confirmed via scanning electron microscope (SEM) with an attached energy-dispersive X-ray spectrometer (EDS), respectively. All luminescence properties have been deeply investigated by excitation spectra, emission spectra, luminescence decay curves and temperature-dependent luminescent spectra. The morphology of the as-prepared phosphor is successfully controlled by adjusting reaction solvents and adding different surfactants. In addition, the optical behaviours of the red phosphors are evidently relied on the experimental procedure, the concentrations of the K₂MnF₆, different surfactants and reaction solvents. Concentration and thermal quenching mechanisms are discussed according to detailed experimental results. A warm white light-emitting diode (WLED) with the as-obtained red phosphor (NH₄)₂NaInF₆:Mn⁴⁺ has been successfully produced, which has low CCT (3960 K), high CIR (R_a = 85.5) and LE of 129 lm W⁻¹. Above results reveal the extraordinary application value of (NH₄)₂NaInF₆:Mn⁴⁺ red phosphor for highly efficient warm WLEDs.