Ultraviolet to near-infrared energy transfer in NaYF_4:Nd~(3+),Yb~(3+) crystals

To convert ultraviolet(UV) light into near-infrared(NIR) light in phosphors is demanded for the development of solar cells.A series of NaYF_4:Nd~(3+),Yb~(3+) white powder samples were prepared via the hydrothermal method.The crystal structure and photoluminescence properties of the samples were carefully studied using X-ray diffractometry(XRD) and photoluminescence spectra.The excitation and emission spectra of NaYF_4:Nd~(3+),Yb~(3+) samples and the luminescence decay curves of Nd~(3+) and Yb~(3+) revealed an efficient energy transfer process from Nd~(3+) to Yb~(3+).This process resulted in the Yb~(3+) NIR fluorescent emission at 980 nm.Moreover,the lifetime of the Nd~(3+4)F_(3/2) level decreased with the increase of Yb~(3+) doping concentration.The build-up time of the decay curves of the Yb~(3+2)F_(5/2) level further verified the energy transfer process.Meanwhile,energy transfer efficiency based on different Yb~(3+) doping concentrations was achieved.