(Ca,Mg,Sr)(9)Y(PO(4))(7):Eu(2+),Mn(2+): Phosphors for white-light near-UV LEDs through crystal field tuning and energy transfer

Abstract

Two series of single-composition (Ca,Mg,Sr)(9)Y(PO(4))(7):Eu(2+) and (Ca(0.5)Sr(0.5))(9)Y(PO(4))(7):Eu(2+),Mn(2+) phosphors were synthesized via high-temperature solid-state reactions. Their emission colors could be tuned from blue to green and eventually to red through tuning the crystal field splitting and energy transfer. On examining the Mn(2+) concentration-dependent photoluminescence properties, we found that co-doping with Mn(2+) would lead to a change in Eu(2+)/Eu(3+) ratio. Moreover, an energy transfer from Eu(2+) to Mn(2+) occurs because of the spectral overlap between the emission band of Eu(2+) and the excitation band of Mn(2+). The resonance-type energy transfer via a dipole-quadrupole interaction mechanism was supported by decay lifetime data and the critical distance of energy transfer was calculated to be 11.09 angstrom A. A trichromatic white-light emitting diode was fabricated by integrating a 380 nm near-ultraviolet (n-UV) chip comprising yellow-emitting (Ca(0.5)Sr(0.5))(9)Y (PO(4))(7):0.007Eu(2+),0.02Mn(2+) and blue-emitting (Ca(0.5)Mg(0.5))(9)Y(PO(4))(7):0.007Eu(2+) phosphors into a single package. Such a composite device emitted white light with a correlated color temperature of 6303 K, a color rendering index of 87.4, and color coordinates (0.314, 0.348) close to those of ideal white light. The results suggest that a phosphor blend of (Ca(0.5)Sr(0.5))(9)Y(PO(4))(7):0.007Eu(2+), 0.02Mn(2+) and (Ca(0.5)Mg(0.5))(9)Y(PO(4))(7):0.007Eu(2+) is potentially useful for white n-UV light-emitting diodes (LEDs).