Room-temperature synthesis, controllable morphology and optical characteristics of narrow-band red phosphor K2LiGaF6:Mn4+

Abstract

A series of red phosphors based on the substitution of Mn⁴⁺ for Ga³⁺ in the lattice of K₂LiGaF₆ were synthesized via a co-precipitation method. Their structure, morphology and composition were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS) in detail. The luminescence properties of the K₂LiGaF₆:Mn⁴⁺ samples were systematically evaluated by photoluminescence (PL) spectroscopy. The excitation spectrum consists of two broad bands from 300 to 550 nm. The obtained K₂LiGaF₆:Mn⁴⁺ can exhibit red light peaking at 636 nm for the ²E_g → ⁴A_2g transition of Mn⁴⁺ ions under 470 nm excitation. A low concentration quenching phenomenon occurs in K₂LiGaF₆:Mn⁴⁺ and the optimal doping concentration is about 4%. The critical distance was calculated to be 9.107 Å. The changes of the emission intensity and morphology of K₂LiGaF₆:Mn⁴⁺ based on different lithium sources and surfactants were investigated in detail. White light-emitting diodes (WLEDs) fabricated from the red K₂LiGaF₆:Mn⁴⁺ phosphor exhibit good performance with a colour rendering index of 79.6, a low colour temperature of 4378 K and a luminous efficiency of 109.91 lm W⁻¹. Therefore, the K₂LiGaF₆:Mn⁴⁺ red phosphors can be used as good candidates for WLEDs.