Up/down conversion, tunable photoluminescence and energy transfer properties of NaLa(WO4)2:Er3+,Eu3+ phosphors

Abstract

Er³⁺ or/and Eu³⁺ codoped NaLa(WO₄)₂ down conversion (DC) and up conversion (UC) phosphors were prepared by a facile hydrothermal process. For NaLa(WO₄)₂:Er³⁺ phosphors, the WO₄²⁻ group can efficiently absorb ultraviolet (UV) light, and emit bright blue and green emissions by the f–f transitions of Er³⁺ through the host sensitization effect. The critical distance of the Er³⁺ ions in NaLa(WO₄)₂ is calculated and the energy quenching mechanism is proven to be a resonant type dipole–dipole interaction. More significantly, in the Er³⁺ and Eu³⁺ codoped NaLa(WO₄)₂ phosphors, the bright green emissions of Er³⁺ ions and the red characteristic emissions of Eu³⁺ ions can be observed, and the Er³⁺–Eu³⁺ energy migration has been demonstrated to be a resonant type of a dipole–dipole mechanism. Color-tunable emissions of NaLa(WO₄)₂:Er³⁺,Eu³⁺ microcrystals are realized under different UV radiation, and this could make them good candidates for use as full-color DC phosphors for near UV-LEDs. More practically, under near infrared (NIR) laser excitation at 980 nm, these phosphors also exhibit intense green and red emissions from the Er³⁺–Eu³⁺ energy transfer process, which causes the observed UC of Eu³⁺. The mechanism of UC luminescence is proposed by the observed dependence of integral intensity on the power of the pumping laser.