Some features of EPR and optical spectra of vanadium in aluminophosphate glasses

Abstract

The EPR and optical spectra of vanadium in glasses of ternary Al 2O 3P 2O 5SiO 2 and Al 2O 3P 2O 5B 2O 3 systems have been measured. The results were compared with earlier data for vanadium in binary phosphate, aluminophosphate and silicaphosphate glasses and with results of de-Biasi for V 4+ in crystalline powder α-crystobalite AlPO 4. The superpositions of two hyperfine spectra (ASB-I and ASB-II) were found for many glasses of ternary systems. Both spectra can be attributed to VO 2+ ions. The intensity ratio of the ASB-II spectrum to ASB-I depends on glass composition but is great (> 7) for all the glasses. Only the ASB-II spectrum was observed in glasses with low concentration of Al 2O 3. The spectral parameters of ASB-II spectrum are g | = 1.916–1.921; g ⊥ 1.980–1.988; A | = (188−190) × 10 −4 cm −1 and A ⊥ = (74–77) × 10 −4 cm −1. Three intense bands at 370, 455 and 700 ans 720 nm observed in these glasses can be attributed to V 3+ ions. The excellent agreement of the parameters of the EPR spectrum of V 4+ ions in crystalline α-crystobalite AIPO 4 and ASB-II spectra in the glasses under study suggest the identical electron structure of the paramagnetic species. This species is believed to be characterized by optical bands at 680 and 790 nm which have been observed by de Biasi. The orbital mixing coefficients indicate strong tetragonal distortion of vanadyl complexes responsible for the ASB-II spectrum. It is assumed that VO 2+ ions responsible for this spectrum act as modifiers fitting into the relatively small holes of the three-dimensional networks of phosphate glasses containing no cations of large radii. The microscopic basicity of oxygens in such holes must be about 0.48.