Single-Component and Warm-White-Emitting Phosphor NaGd(WO_4)_2:Tm~(3+), Dy~(3+), Eu~(3+): Synthesis, Luminescence, Energy Transfer, and Tunable Color

摘要

Tm~(3+), Dy~(3+), and Eu~(3+) codoped NaGd(WO_4)_2 phosphors were prepared by a facile hydrothermal process; they were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectrometer (EDS), photoluminescence spectra, and fluorescence lifetime. The results show that the novel octahedral microcrystals with a mean side length of 2 μm are obtained. Under the excitation of ultraviolet, individual RE~(3+) ion (Tm~(3+), Dy~(3+), and Eu~(3+)) activated NaGd(WO_4)_2 phosphors exhibit excellent emission properties in their respective regions. Moreover, when codoping Dy~(3+) and Eu~(3+)/Tm~(3+) in the single component, the energy migration from Dy~(3+) to Eu~(3+) has been demonstrated to be a resonant type via a dipole-quadrupole mechanism as well as that from Tm~(3+) to Dy~(3+) ions, of which the critical distance (RDy-Eu) is calculated to be 11.08 ?. More significantly, in the Tm~(3+), Dy~(3+), and Eu~(3+) tridoped NaGd(WO_4)_2 phosphors, the energy migration of Tm~(3+)-Dy~(3+)-Eu~(3+), utilized for sensitizing Eu~(3+) ions besides compensating the red component at low Eu~(3+) doping concentration, has been discussed first. In addition, under 365 nm near-ultraviolet radiation (nUV), the color-tunable emissions in octahedral NaGd(WO_4)_2 microcrystals are realized by giving abundant blue, green, white, yellow, and red emissions, especially warm white emission, and could be favorable candidates in full-color phosphors for nUV-LEDs.