The energy transfer phenomena and colour tunability in Y2O2S:Eu3+/Dy3+ micro-fibers for white emission in solid state lighting applications

Abstract

This paper reports on the structural, optical and photometric characterization of an Eu³⁺/Dy³⁺ doped yttrium oxysulfide phosphor (Y₂O₂S:Eu³⁺/Dy³⁺) for near white emission in solid state lighting. A series of Y₂O₂S phosphors doped with Eu³⁺/Dy³⁺ were prepared by the hydrothermal method. The microstructures of the as-synthesized phosphors were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results reveal that the obtained powder phosphors have a single-phase hexagonal structure and also indicate that the incorporation of the dopants/co-dopants did not affect the crystal structure. The SEM images reveal the morphology of the prepared phosphors as an intense interpenetrating network of interconnected micro-fibers with a diameter of about 0.15 μm. The band gap of the phosphors was calculated from diffuse reflectance spectra using the Kubelka–Munk function. The Eu³⁺, Dy³⁺ doped and Eu³⁺/Dy³⁺ co-doped phosphors illuminated with ultraviolet light showed characteristic red luminescence corresponding to the ⁵D₀→⁷F_J transitions of Eu³⁺ and characteristic blue and yellow luminescence corresponding to the ⁴F_9/2→⁶H_15/2 or ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺. The luminescence spectra, the energy transfer efficiency and the decay curves of the phosphors indicated that there exists a strong energy transfer from Dy³⁺ to Eu³⁺ and this was demonstrated to be a resonant type via a dipole–quadrupole reaction. Furthermore, the critical distance of the Eu³⁺ and Dy³⁺ ions have also been calculated. By utilizing the principle of energy transfer it was also demonstrated that with an appropriate tuning of the activator content the Y₂O₂S:Eu³⁺/Dy³⁺ phosphors can exhibit a great potential to act as single-emitting component phosphors for white light emission in solid state lighting technology.