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Intense blue emission of perovskite-type fluoride phosphor Cs4Mg3CaF12: Eu2+ as a promising pc-WLEDs material

Xinyi Zhang,Jian-Feng Sun

An intriguing novel perovskite-type Cs 4 Mg 3 CaF 12 : Eu 2+ phosphor with desirable properties for potential application in the field of white light-emitting diodes was first time synthesized. The Rietveld structural refinement, scanning electron microscopy and high resolution transmission electron microscopy were used to determine the crystallographic parameters, morphology and microstructure of Cs 4 Mg 3 CaF 12 : Eu 2+ phosphor. The first principle calculation based on the density functional theory further provided a theoretical understanding of the band structure for the undoped Cs 4 Mg 3 CaF 12 and indicated that it has a large direct band gap of 7.1 eV. Upon the excitation of Cs 4 Mg 3 CaF 12 : Eu 2+ phosphor in the broad range of 250–450 nm, the bright blue light emission was observed with the maximum at 474 nm and a full width at half-maximum of 2808 cm −1 that was attributed to the electric-dipole allowed 4f 6 5 d 1 →4f 7 transition of Eu 2+ ions. Based on the Dexter’s theory, the concentration quenching mechanism among Eu 2+ in the Cs 4 Mg 3 CaF 12 : Eu 2+ phosphor was validated to be the dipole-dipole interaction, and the critical distance was determined to be 23.34 Å. On the basis of temperature-dependent luminescence measurement, an analysis of the origins of thermal quenching behavior was presented. The Cs 4 Mg 3 CaF 12 : Eu 2+ phosphor not only has favorable thermal stability with emission intensity reduction by 20% at T = 473 K in reference to the room temperature level, but also shows the integrated PL intensity 95% as high as that of BaMgAl 10 O 17 : Eu 2+ , internal quantum efficiency of 64% and color purity of 85%. The results of this work indicate that the blue-emitting Cs 4 Mg 3 CaF 12 : Eu 2+ phosphor with promising luminescence properties has a capacity for incorporation as a component to the near-UV based phosphor-converted WLEDs.