Color-Tunable Phosphor of Eu2+ and Mn2+ Codoped Ca2Sr(PO4)2 for UV Light-Emitting Diodes

A series of color-tunable phosphors, Ca2Sr(PO4)(2):Eu2+, Mn2+, were synthesized via high-temperature solid-state reaction. The photoluminescence emission and excitation spectra, thermal-dependent luminescence quenching properties, color coordinates, the mechanism of concentration quenching, and energy transfer are investigated systematically. The results show that there is an efficient nonradiative energy transfer from Eu2+ to Mn2+, of which the efficiency is about 91.8%. Mn2+ emits an intense reddish-orange light by the sensitization of Eu2+. At the same time, Eu2+ gives a strong excitation band at 250-420 nm, matching well with the emission band of near-ultraviolet [(n)-UV] (350-420 nm) light-emitting diodes (LEDs). Phosphor-converted LEDs were fabricated by coating Ca2Sr(PO4)(2):Eu2+ and Ca2Sr(PO4)(2):Eu2+, Mn2+ phosphors onto (n)-UV chip emitting at 392 nm. The results indicate that because of the energy transfer from Eu2+, Mn2+ with weak d-d absorption intensity in the (n)-UV region can also be used as an activator in reddish-orange-emitting phosphors for in (n)-UV LEDs.