Hydrothermal synthesis and tunable luminescence of YPO4:Eu2+/Eu3+, Tb3+ nanocrystals

Abstract

The homogeneous and well crystallized rare earth ions RE3+ (RE = Eu, Tb) doped YPO4 and YPO4·0.8H2O nanocrystals (NCs) are synthesized by a simple hydrothermal route. The samples are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. The results indicate that the pH value of precursor affects the phase composition and surface morphology of the final product. The results of XPS indicate that both Eu2+ and Eu3+ co-exist in YPO4 NCs, implying that the self-reduction from Eu3+ to Eu2+ takes place with the absence of reducing agents, charge compensation reagents and charge carrier trapping processes. In addition, YPO4:Eu and YPO4·0.8H2O:Eu samples exhibit strong and bright blue and red emission. According to PL spectroscopy, the blue emission is originated from host lattice and Eu2+ ion luminescence and red emission from Eu3+. YPO4:Tb, Eu samples can be effectively excited at 355 nm. An energy transfer phenomenon appears between Tb3+ and Eu3+. It is interesting that by changing the concentration of Tb3+, white phosphor from Y0.90PO4:0.04 Tb, 0.06Eu NCs are successfully obtained. Moreover, the Y0.90PO4:0.04 Tb, 0.06Eu has excellent thermal stability. These results indicate that the combination of defect and rare earth luminescence in YPO4:Tb, Eu NCs can produce tunable luminescence color, which may have potential applications in fields such as solid-state lighting and field emission displays.