Luminescence properties of Eu3+-activated SrWO4 nanophosphors-concentration and annealing effect

Abstract

Eu³⁺ (2, 5, 7 and 10 at.%) activated SrWO₄ phosphors were prepared via a polyol synthesis route at low temperature (∼150 °C) under urea hydrolysis. X-ray diffraction studies of all Eu³⁺ doped samples corroborate good crystallinity with a tetragonal scheelite-type structure of the SrWO₄ phase. The value of strain was obtained in the range ∼0.003 to 0.004 for as-prepared (ASP) and samples annealed at 900 °C. Vibrational modes were studied using IR and Raman Spectroscopy. Photoluminescence studies of Eu³⁺ doped SrWO₄ samples were carried out under 266, 394 and 464 nm excitations. An intense red emission was observed with a strong peak at ∼613 nm due to ⁵D₀ → ⁷F₂ transition under 266 nm. Effect of annealing at 900 °C on the photoluminescence properties of samples has been studied and it was found that luminescence intensity increases up to ∼9 times (for 10 at.% Eu³⁺-doped SrWO₄) on annealing as compared to the corresponding as-prepared sample. High asymmetric ratios (A₂₁) ∼ 6–13 were observed demonstrating it to be a red emitter. Calculated CIE co-ordinates of these Eu³⁺ doped samples under 266 nm excitation for ASP and annealed at 900 °C are x = 0.65 & y = 0.34, which are closer to the standard of NTSC (x = 0.67 & y = 0.33). These studies reveal that SrWO₄:Eu³⁺ nano-phosphors can be used as potential red emitting phosphors for the development of white LEDs.