Eu3+ co-doped Sr3Gd(PO4)3:Dy3+ phosphors: luminescence properties and color-tunable white-light emission for NUV-WLEDs

A series of Dy3+ and Eu3+ co-doped Sr3Gd(PO4)(3) phosphors were synthesized by a high-temperature solid-state method. The crystal structure, optical band gap energy, luminescence properties, concentration quenching, energy transfer process and thermal stability were investigated. All the phosphors are pure eulytite-type Sr3Gd(PO4)(3) in structure. Under different wavelengths' excitation, the Sr3Gd(PO4)(3):Dy3+, Eu3+ phosphors exhibit different emission intensities for Eu3+ and Dy3+. The color and correlated color temperature (CCT) can be tuned from cool white to warm white by adjusting excitation wavelengths and the doping concentration of Eu3+. Under the 351-nm excitation, the optimal Sr3Gd(PO4)(3):0.03Dy(3+), 0.085Eu(3+) phosphor displays a warm white emission with CIE coordinate of (0.3987, 0.3613), CCT of 3409 K, internal quantum efficiency of 44.8% and activation energy of 0.1883 eV. These results suggest that single-phased white-emitting phosphors Sr3Gd(PO4)(3):Dy3+, Eu3+ can be used in the near-ultraviolet light-emitting diodes.