Green route, room-temperature synthesis and luminescence properties of a non-rare-earth doping Zn2+ based narrow-band red phosphor for WLEDs

Highlights: • KZnF₃:Mn⁴⁺ red phosphors were synthesized by green route. • Concentration quenching mechanism was systematically discussed. • The KZnF₃:Mn⁴⁺ red phosphors as expected exhibit a sharp narrow-band red emission. • The KZnF₃:Mn⁴⁺ can be used as a red component to improve the performance of WLEDs. -- Abstract: As a promising red component used in white light-emitting diodes (WLEDs), Mn⁴⁺ activated fluoride red phosphor has drawn tremendous attention due to its excellent luminescence properties. However, in order to synthesize these phosphors, the hypertoxic HF which will cause safety problems has to be used. In this work, a class of KZnF₃:Mn⁴⁺ phosphors were synthesized by using low toxicity (HCl + NH₄F) to substitute for HF at room temperature. The structure, morphology and element composition have been analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometers (EDS) in detail, respectively. The optical properties of KZnF₃:Mn⁴⁺ were evaluated and we found that under blue light excitation, KZnF₃:Mn⁴⁺ as expected exhibits a sharp narrow-band red emission near 636 nm. In addition, the synthesis parameters, including the molar ratios of (HCl + NH₄F) to Zn(NO₃)₂·6H₂O and reaction time on the luminescent properties of KZnF₃:Mn⁴⁺ samples have been systematically discussed. Furthermore, the concentration quenching mechanism was also analyzed. Finally, it is assembled by YAG:Ce³⁺, KZnF₃:Mn⁴⁺ and blue LED chip to achieve a WLED with a lower CCT (4974 K), higher CRI (Ra = 82.1) and a luminous efficiency of 120.33 lm/W. All of these results manifest that the KZnF₃:Mn⁴⁺ phosphors prepared by green route would be a satisfactory material to ameliorate the performance of WLEDs.