Structure and luminescence properties of the novel multifunctional K2Y(WO4)(PO4):Ln3+ (Ln = Tb, Eu, Yb, Er, Tm and Ho) phosphors
Lanthanide ion (Tb, Eu, Yb, Tm, Er, and Ho) activated multifunctional phosphors K2Y(WO4)(PO4), (KYWP) were prepared via a conventional solid-state reaction. The crystal structure of KYWP as a new host matrix for luminescence was firstly defined to be the orthorhombic system with space group Ibca (73) via Rietveld refinement of the powder X-ray diffraction and the GSAS software. The vacuum ultraviolet (VUV) excited photoluminescence and cathodoluminescence (CL) analysis of individual Tb3+/Eu3+ activated KYWP phosphors exhibit excellent emission properties in their respective regions. Both KYWP:Tb3+ and KYWP:Eu3+ had high quenching concentration under 147 nm excitation attributed to a long Y–Y distance in KYWP structure, whereas they showed very low quenching concentration under low-voltage electron-beam excitation. This phenomenon was ascribed to the different mechanisms between CL and VUV excited luminescence. Under 980 nm laser excitation, yellow, purple, and red up-conversion (UC) emissions had been achieved in Yb3+–Er3+, Yb3+–Tm3+, and Yb3+–Ho3+ co-doped KYWP, respectively. In Yb3+–Tm3+–Ho3+ tridoped KYWP, red emissions emerging from transitions of Tm3+ changed to the transitions of Ho3+. And the possible reason had been elucidated by a cross-relaxation process between Tm3+ and Ho3+. Laser power dependence of the UC emissions and the energy level diagrams were studied to understand the UC and cross-relaxation mechanisms. The obtained results indicated that the multifunctional lanthanide ion doped KYWP exhibited excellent VUV photoluminescence, CL and multicolor UC luminescence properties.