Investigation of Ba_1-2xEu_xNa_xWO₄ and Ba_1-2xEu_xK_xWO₄ luminescent properties under UV excitation or X-rays

Full text: Tungstates of composition MWO₄ (M= Ca, Ba, Pb or Cd) are commonly used in electro-optical devices. Ca, Pb and Cd tungstates have good scintillation properties, but BaWO₄ shows no emission when excited with X-rays, its properties can be favored by doping with rare earth ions and co-doping with alkaline metals. According to ROMERO et al. [1] Ba_1-xEu_xWO₄ (x=1 or 3 %) samples do not show emission when excited by X-ray beams. However when co-doped with Li⁺ the sample exhibits emission. In these cases different excitation and emission mechanisms can take place. The aim of this work is to study the structural and optical properties by exchanging Li⁺ for M⁺ (M⁺=Na⁺ or K⁺ ). The samples Ba_1-2xEu_x M_xWO₄ (x=1; 3 or 5%) were prepared by modified Pechini method. Characterization was done by X-ray diffraction (XRD), vibrational spectroscopies by infrared absorption (FT-IR) and Raman scattering (Raman), electronic spectroscopies by UV-VIS diffuse reflectance (DRS), and UV and X-rays (Cu K_a ) excited luminescence (FL and XEOL). FTIR, Raman and XRD, show the BaWO₄ I41/a space group with short distance defects. The absorption edge shift to longer wavelength with a higher percentage of dopant and co-dopant suggests an increase in the quantity of deep defects. The FL spectra show Eu³⁺ ions at low symmetry site, without inversion center. The XEOL results suggest an increase in the defects with increasing dopant and co-dopant amount. The luminescence pattern excited by UV and X-rays is not a function of co-dopant type; however the emission intensities depend on dopant and co-dopant amount. (author)