A red-emitting Mn4+ activated phosphor with controlled morphology and two-dimensional luminescence nanofiber film: Synthesis and application for high-performance warm white light-emitting diodes (WLEDs)

Mn4+ activated fluoride red phosphors, Na2GeF6:Mn4+, with controllable morphology and size, were successfully synthesized through simple coprecipitation method. Using the hollow Na2GeF6:Mn4+ particles, we successfully fabricated two-dimensional red-emitting nanofiber film via electrospinning technology. The phase purity, morphology and composition of the samples were confirmed via X-ray powder diffraction (XRD), scanning electron microscope (SEM) and energy-dispersive X-ray spectrometer (EDS), respectively. Different surfactants were introduced into the experimental process, which successfully controlled the sample morphology. The broad excitation band from 300 nm to 550 nm matches well with commercial blue light emitting diodes, and narrow band emission red light can be observed in the range of 575-675 nm because of spin-forbidden E-2(g) - (4)A(2g) energy level transition of Mn4+ ion. The effect of doping concentration on luminescence and the mechanism of concentration quenching were discussed. On the basis of the experimental excitation (PLE) and emission (PL) spectra, the crystal field strength of the Mn4+ occupation environment was estimated and the nephelauxetic effect was researched for the Mn4+ ions in the Na2GeF6 host. Temperature-dependent properties of Na2GeF6:Mn4+ particles and nanofiber film were systematically analysed. Moreover, the Na2GeF6:Mn4+ particles and nanofiber film can significantly change the performance of white light-emitting diodes (WLEDs), the nanofiber film is a more appropriate candidate than Na2GeF6:Mn4+ particle for warm WLED applications. (C) 2019 Published by Elsevier B.V.