ELECTRON-STIMULATED SONOCHEMILUMINESCENCE OF Ce3+ IN LIQUID AMMONIA

Abstract

For the first time, the phenomena of light emission during the sonolysis of liquid ammonia and solutions of cerium and silver salts in it at – 70 °C were considered. The presence of a Ce³⁺ luminescence band with a maximum of 400 nm in the spectrum of moving single-bubble sonoluminescence generated by ultrasound in the solution of 5 * 10^-4 M Ce(SO₄)₂ in ammonia was discovered. This band was found in addition to the bubble luminescence continuum usual for liquids (240—800 nm in ammonia). This band is quenched in the presence of 10^-2 M AgNO₃ in the solution. This indicates the suppression of Ag⁺, the electron acceptor, of the probable reaction of sonochemiluminescence Ce⁴⁺ + e_s^– →η(Ce³⁺)* + (1– η)Ce³⁺, (Ce³⁺)*→Ce³⁺ + hν, responsible for the detected Ce³⁺ glow. The concentration of Ce⁴⁺ in the solution decreases when it is reduced by this reaction, and the intensity of sonochemiluminescence in the Ce³⁺ band decreases during sonolysis, but reaches a constant level a few minutes after its start. This is explained by the achievement of dynamic equilibrium between the rates of reduction and oxidation reactions of cerium ions: Ce⁴⁺→Ce³⁺ and Ce³⁺→Ce⁴⁺, respectively. The one-electron oxidizing agent in the last reaction is presumably the NH₂ radical, another primary product of ammonia sonolysis, in addition to e_s^– . The formation of Ce³⁺ during sonolysis of a Ce(SO₄)₂ solution was confirmed by registration of Ce³⁺ photoluminescence in it. The excitation yield in the sonochemiluminescence reaction was estimated to be η = 2 * 10^-6.