Preparation of novel color tunable Na2Ca(PO4)F:Eu2+,Mn2+ phosphors for sunlike LED applications

Abstract

A series of color-tunable Na₂Ca(PO₄)F:Eu²⁺, Mn²⁺ phosphors were prepared by solid state reaction. The structure, as well as the photoluminescent properties of the as-prepared phosphor were investigated. The energy transfer process between Eu²⁺-Mn²⁺ was also discussed. The phosphor demonstrates luminescence in the range of 420 nm–750 nm under UV excitation. Specifically, the emission spectra comprise green light (420–550 nm) attributed to the 4f-5d transition of Eu²⁺ ions, and orange red light (550–750 nm) resulting from the ⁶A₁→⁴A₁(⁴G), ⁴E(⁴G) transitions of Mn²⁺ ions. An effective dipole-dipole energy transfer has been confirmed to occur between the co-doped Eu²⁺ and Mn²⁺ ions. The luminescent color of the as-prepared phosphors can change from blue to yellow, and finally to orange red by adjusting the doping amount of the co-doped ions. The optimal sample's EQE reached 20.59% due to the high absorption efficiency. Finally, a 400 nm violet light chip excited white LED with a high color rendering index (CRI) of Ra = 98 was fabricated by using the as-prepared Na₂Ca(PO₄)F:0.02Eu²⁺,0.04Mn²⁺ phosphor in combination with the commercial blue Sr₅(PO₄)₃Cl:Eu²⁺ phosphor and red CaAlSiN₃:Eu²⁺ phosphor. The results indicated that the developed phosphor holds notable potential for application in in the field of sunlike healthy lighting.