Raman Spectroscopic Study of Solid-State and Sol–Gel Znwo₄ and the Effect of Eu³⁺ Doping Concentration on Vibrational Properties

The Raman spectra of pure ZnWO₄ prepared by solid-state and sol–gel methods and of solid-state ZnWO₄ doped with 1% and 2% Eu³⁺ were investigated. All samples showed the characteristic monoclinic wolframite spectrum, dominated by the symmetric W–O stretching band near 907 cm⁻¹. The 1% and 2% Eu³⁺ samples, measured under identical conditions, gave practically identical spectra, with band positions agreeing within 0.1–0.3 cm⁻¹, equal linewidths and no new bands, so no Eu³⁺-dependent change of the WO₆ framework was detected. The uniform downshift of about 1 cm⁻¹ of all bands relative to the pure solid-state sample was attributed to the different excitation wavelength and grating, not to doping. The sol–gel sample showed slightly lower band positions, broader low-frequency bands, a strong fluorescent background and a weak band near 926 cm⁻¹, indicating somewhat lower structural order.