Highly efficient infrared to visible up-conversion emission tuning from red to white in Eu/Yb co-doped NaYF phosphor.

Eu/Yb co-doped NaYF phosphors have been synthesized by the combustion method. The Eu doping was fixed and the effect of Yb doping concentration on the structural, morphological and luminescence properties has been investigated. X-ray diffraction analysis revealed that the phosphors consisted of mixed α- and β-phases, but the β-phase was dominant. All elements of the host and dopants, as well as adventitious C, were detected using X-ray photoelectron spectroscopy. The surface morphology showed a microrod-like structure with sharp hexagonal edges. Energy dispersive X-ray spectroscopy spectra proved the formation of the desired materials. The photoluminescence spectra illustrated the optical emission properties of Eu in the red region when excited at 394 nm, while, under the same excitation, Yb ions gave emission at 980 nm. The up-conversion (UC) emission of Eu/Yb co-doped NaYF produced a white color at the higher concentration of Yb excited by a 980 nm laser, which was made possible by green emission of Er contamination (from Yb source) and blue emission of Eu ions. The lifetime of the Eu UC luminescence at 615 nm was also affected by the Yb doping concentration. The temperature sensitivity associated with the Er peaks at 520 and 542 nm was assessed as a function of temperature and the maximum of 0.0040 K occurred at 463 K.