Nonstoichiometric LaO_0.65F_1.7 Structure and Its Green Luminescence Property Doped with Bi³⁺ and Tb³⁺ Ions for Applying White UV LEDs

Abstract

Red–green–blue phosphors excited by ultraviolet (UV) radiation for white light LEDs have received much attention to improve the efficiency, color rendering index (CRI), and chromatic stability. The spectral conversion of a rare-earth ion-doped nonstoichiometric LaO0.65F1.7 host was explored with structural analysis in this report. The nonstoichiometric structure of a LaO0.65F1.7 compound, synthesized by a solid-state reaction using La2O3 and excess NH4F precursors, was analyzed by synchrotron X-ray powder diffraction. The crystallized LaO0.65F1.7 host, which had a tetragonal space group of P4/nmm, contained 9- and 10-coordinated La3+ sites. Optical materials composed of La1−p−qBipTbqO0.65F1.7 (p = 0 and 0.01; q = 0–0.2) were prepared at 1050 °C for 2 h, and the single phase of the obtained phosphors was indexed by X-ray diffraction analysis. The photoluminescence spectra of the energy transfer from Bi3+ to Tb3+ were obtained upon excitation at 286 nm in the nonstoichiometric host lattice. The desired Commission Internationale de l’Eclairage (CIE) values of the phosphors were calculated. The intense green La0.89Bi0.01Tb0.1O0.65F1.7 phosphor with blue and red optical materials was fabricated on a 275 nm UV-LED chip, resulting in white light, and the internal quantum efficiency, CRI, correlated color temperature, and CIE of the pc LED were characterized.

Keywords

• X-ray diffraction
• phosphors
• Bi³⁺
• Tb³⁺ energy transfer
• pc LED