Structural, optical spectroscopy and energy transfer features of Tb3+-activated (Y, Gd)F3 nanophosphors for UV-based LEDs

Abstract

Rare earth activated nanofluorides have attracted attention due to their interesting optical properties and diverse applications endowed by their low phonon energy. In this study, a series of (Y_0.95−x, Gd_0.05) F₃:xTb³⁺ (x = 0, 0.01, 0.03, 0.05, 0.07, 0.10) nanophosphors were fabricated via a hydrothermal synthesis route. The structures, morphologies, and optical properties of the synthesized nanophosphors were analyzed in detail using X-ray diffractometry, vibrational spectroscopies, transmission electron microscopy, X-ray photoelectron spectroscopy, and diffuse reflectance spectroscopy. The characteristic emissions of both the Gd³⁺ (⁶P_7/2 → ⁸S_7/2) and Tb³⁺ (⁵D₄ → ⁷F_j) ions can be observed in the photoluminescence spectra at the 272 nm excitation of Gd³⁺ ions and the Gd³⁺ → Tb³⁺ energy transfer leading to 15-fold enhancement in the green emission of the trivalent terbium ion is discussed thoroughly. The possible energy transfer mechanism from Gd³⁺ to Tb³⁺ is presented schematically and 88.92% energy transfer efficiency was achieved, which is dominated by electric dipole–dipole interactions. The calculated branching ratio (for ⁵D₄ → ⁷F₅), quantum efficiency of 89% and obtained colorimetric parameters suggest the applicability of the synthesized nanophosphors in ultraviolet excitable phosphors for white light-emitting diodes and solid-state green lasers.