Tunable luminescence and energy transfer properties of NaGdF4:Dy3+, Eu3+ nanophosphors

Abstract

A series of tunable luminescence NaGdF₄:Dy³⁺, Eu³⁺ nanophosphors have been synthesized for the first time by a one-step hydrothermal method. X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), X-ray energy dispersive spectrometer (EDS) and photoluminescence (PL) spectroscopy were employed to characterize the samples. Under the excitation of UV light, NaGdF₄:Dy³⁺ and NaGdF₄:Eu³⁺ exhibit the characteristic emissions of Dy³⁺ (⁴F_9/2 → ⁶H_15/2, blue and ⁴F_9/2 → ⁶H_13/2, yellow) and Eu³⁺ (⁵D₀ → ⁷F₂, red), respectively. It is found that in a Dy³⁺, Eu³⁺-codoped NaGdF₄ system, the energy is transferred from Dy³⁺ to Eu³⁺ by the photoluminescence spectra and faster decay times of the blue emissions from energy donors (Dy³⁺). Moreover, the energy transfer is efficient and certified to be a resonant type via a quadrupole–quadrupole interaction by comparing the experimental data and theoretical calculation. The corresponding luminescence and energy transfer mechanisms have been proposed in detail. Most interestingly, the white light with varied hues has been obtained in Dy³⁺ and Eu³⁺ co-activated NaGdF₄ phosphors by utilizing the principle of energy transfer and properly designed activator contents. The results show that the obtained nanophosphors have a promising application in display and lighting fields.