Efficient blue-white color luminescence with near-ultraviolet excitation in Dy3+/Tm3+:Na3Gd(PO4)2 nanophosphor for white LEDs

The Dy3+, Tm3+ ions activated, and Dy3+/Tm3+ ions co-activated Na3Gd(PO4)(2) phosphors were synthesized by the citrate-gel based combustion technique. The structural properties of as-synthesized phosphors were studied through X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The influence of Tm3+ concentration on the fluorescence properties of Na3Gd(PO4)(2):Dy3+/Tm3+ phosphors were systematically investigated under near-UV light irradiation of 359 and 352 nm. The energy transfer efficiency (eta(ET)) of as-prepared phosphors increases gradually from 17 to 42%, and the critical distance (R-c) between Dy3+ and Tm3+ ions is calculated to be 4.76 angstrom. For better understanding the energy transfer mechanism (ET:Dy3+-> Tm3+), the decay curves were utilized on the basis of Dexter's energy transfer formula and Reisfeld's approximation. More importantly, the obtained CIE color coordinates of Na3Gd(PO4)(2):Dy3+/Tm3+ phosphors located at blue-white region under near-UV light irradiation. The results demonstrate the promising application of Na3Gd (PO4)(2):Dy3+/Tm3+ phosphor for near-UV white LEDs.