Emission red shift and energy transfer behavior of color-tunable KMg4(PO4)3:Eu2+,Mn2+ phosphors
Abstract
Eu2+- and Mn2+-co-doped KMg4(PO4)3 phosphors were prepared via conventional high temperature solid-state reactions. Their crystal structures, luminescence properties, emission red shifts, and energy transfer between Eu2+ and Mn2+ were investigated systematically. Under excitation at 365 nm, KMg4(PO4)3:Eu2+,Mn2+ phosphors exhibited a broad excitation band ranging from 250 to 425 nm and two broad emission bands that peaked at 450 nm and 625 nm, which were ascribed to the 4f–5d transition of Eu2+ and the 4T1 → 6A1 transition of Mn2+ ions, respectively. Three emission bands of Mn2+ were observed in KMg4(PO4)3: Eu2+,Mn2+, which can be attributed to the disordering of Mn2+ in the Mg2+ sites to form different luminescence centers. The energy transfer between the Eu2+ and Mn2+ ions is of a resonant type via a dipole–quadrupole mechanism. The emission red shift that takes place with increasing Mn2+ concentration and operating temperature are discussed in relation to the crystal structure and energy transfer in KMg4(PO4)3:Eu2+,Mn2+. Utilizing the redshift and the energy transfer from Eu2+ to Mn2+, KMg4(PO4)3:Eu2+,Mn2+ phosphors can be tuned from blue to pink by appropriate adjustment of the Mn2+ content and may have potential application for white light-emitting diodes and plantlet culturing.