Sm3+ doped K3Gd3B4O12: An orange-emitting phosphor for white light-emitting diodes

K3Gd3-xSmxB4O12 orange phosphors were synthesized via the high temperature solid-state reaction method. The phase composition, morphology, particle size and luminescent properties were investigated using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra (PL), respectively. The SEM images showed that the doped sample exhibited an irregular morphology with e diameter of about 2 μm. The optimum doping concentration was found to be 15 mol% for Sm3+ ion and the critical distance Rc was calculated to be 7.8846 Å. Under near-UV light (405 nm) excitation, they showed intense orange emission centered at 603 nm because of the 4G5/2 → 6H7/2 transition of Sm3+ activator. Under 276 nm excitation, there existed a charge transfer from Gd3+ to Sm3+ and the charge transfer efficiency of K3Gd3-xSmxB4O12 can reach 99.88%. The CIE coordinates of phosphor K3Gd2.85Sm0.15B4O12 are calculated to be (0.5895, 0.4096) and the color purity was estimated to be around 88%, which indicates that the phosphor may be potentially excited NUV chips for application in W-LEDs.