Preparation and Characterization of LaF₃:Eu³⁺ red phosphors as white LED

Nanophosphors LaF₃:Eu³⁺ with hexagonal structure have been prepared by hydrothermal method.The properties of the resulting phosphors are characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), photoluminescence (PL) spectra and decay curve.The excitation spectra of LaF₃:Eu³⁺ phosphors are mainly consists of the band at about 250 nm that corresponding to O^2-→Eu³⁺ charge-transfer (CT) and some sharp lines of Eu³⁺ f-f transitions in the near ultraviolet region with one intense peak at about 396 nm.The emission spectra were used to probe the local environments of Eu³⁺ ion in LaF₃ crystal.Based on the emission and excitation spectra at 298K, it is identified that the lattice site of Eu³⁺ in tetragonal LaF₃ nanocrystals descending from D_4h to approximate C_2v as a result of the lattice distortion.Under the 396 nm excitation, strong red emission peaked at 591 nm attributed to ⁵D₀→⁷F₁ transition of Eu³⁺ are observed for 10 % LaF₃:Eu³⁺ phosphors as the optimal doping concentration.The luminescence properties show that LaF₃:Eu³⁺ phosphor may be considered to be a potential red phosphor candidate for near-UV light emitting diodes (LEDs).