Abstract: LnBO₃:Eu(Ln=Y,Gd)orthoborates were prepared by solid state reaction and sol-gel technique. Nephelauxetic effect was observed in the ⁷F₀→⁵D₀ transition of Eu³⁺ in a pseudo-vaterite type YBO₃ when the
excitation spectra were carried out at different temperatures. According to the luminescence of YBO₃:Eu at low temperatures and the effect of
different temperatures on the luminescence, the site symmetries of Ln³⁺ in YBO₃ were revised to be a D₃ and a similar C₃. Different
luminescent intensities and quenching concentrations were found for the sol-gel samples and corresponding solid-state-synthesized ones. The effect
of defects or dislocations was taken into account to explain these phenomena. The luminescence of annealed samples and the Raman spectra of them suggested the
presence of Eu³⁺ clusters in the sol-gel crystalline YBO₃:Eu.

Key words: YBO₃, sol-gel technique, luminescence, nephelauxetic effect