Designed synthesis, morphology evolution and enhanced photoluminescence of a highly efficient red dodec-fluoride phosphor, Li₃Na₃Ga₂F₁₂:Mn⁴⁺, for warm WLEDs

Red phosphors of the Mn⁴⁺ doped dodec-fluoride Li₃Na₃Ga₂F₁₂:Mn⁴⁺ (LNGF:Mn) with various morphologies have been synthesized from K₂MnF₆, LiF, NaF and Ga₂O₃ in HF at room temperature with excess LiF and NaF relative to the stoichiometric composition of LNGF:Mn. The formation mechanism of the red phosphor LNGF:Mn has been discussed based on detailed experimental results compared with that of the identified phosphor Li₃Na₃Al₂F₁₂:Mn⁴⁺ (LNAF:Mn). The optical properties of LNGF:Mn have been systematically investigated and compared with those of red phosphors Li₃GaF₆:Mn⁴⁺ (LGF:Mn), Na₃GaF₆:Mn⁴⁺ (NGF:Mn) and LNAF:Mn in detail. It is observed that the as-obtained phosphor LNGF:Mn exhibits superior properties in chromaticity coordinates as well as a high luminescence efficiency with a strong potential to enhance the performance of solid-state lighting. The HF-concentration-dependent morphologies of the phosphor LNGF:Mn have been investigated by scanning electron microscopy (SEM). The luminescence of the phosphor LNGF:Mn has been enhanced by optimizing the synthetic parameters, such as the concentrations of HF and K₂MnF₆. The white light-emitting diode (WLED) encapsulated with the as-obtained red phosphor LNGF:Mn and a commercial yellow one, Y₃Al₅O₁₂:Ce³⁺ (YAG:Ce), on a GaN chip produces a warm white light with a color rendering index (CRI) of 91.32 at a correlated color temperature (CCT) of 3986.08 K.