Ca_9La(PO_4)_7:Eu^2+,Mn^2+: an emission-tunable phosphor through efficient energy transfer for white light-emitting diodes

We have synthesized a series of single-composition emission-tunable Ca(9)La(PO(4))(7):Eu(2+),Mn(2+) (CLP:Eu(2+),Mn(2+)) phosphors by solid state reactions. Through an effective resonance-type energy transfer, the CLP:Eu(2+),Mn(2+) phosphors exhibit a systematically varied hues from green, yellow, and eventually to red and the relative intensity of green and red emissions can be tuned by adjusting the concentration of Mn(2+), respectively. The energy transfer from Eu(2+) to Mn(2+) in CLP:Eu(2+),Mn(2+) has been studied and demonstrated to be a resonant type via a dipole-quadrupole mechanism based on the decay lifetime data and the energy transfer critical distance was estimated to be 11.36 A by using the spectral overlap methods. A warm white light emitting diode (WLED) with CIE chromaticity coordinates of (0.35, 0.31), superior color-rendering index (Ra) of 91.5 and lower correlated color temperature (CCT) of 4,496 K was fabricated by combining a 365 nm UV-InGaN chip and a phosphor blend of yellow-emitting (Ca(0.98)Eu(0.005)Mn(0.015))(9)La(PO(4))(7) and blue-emitting BaMgAl(10)O(17):Eu(2+).