Generation of Eu(II) excited state during thermolysis of Eu(III) dihydroxyazide

Abstract

It was found that the solid phase thermal decomposition of europium (III) dihydroxyazide at the temperatures above 160 °C is accompanied by chemiluminescence (CL). The emission is observed in the 390–490 nm region of the optical spectrum with a maximum at 458 nm. The emitter of photons was found to be the reaction intermediate – electron-excited *Eu2+ ion coordinated with hydroxyl groups. The formation of divalent europium during the reaction has been confirmed by a set of experimental methods, including luminescence and thermogravimetric analysis as well as diffuse reflectance spectroscopy. It has been established that the stable solid product of the Eu(OH)2N3 thermolysis at the 160–340 °C temperature range is the mixed oxide-hydroxide of europium (III). A possible reaction mechanism is discussed. Thermal activation of the azide anion above 160 °C triggers the electron transfer from the anion to the Eu3+ ion inside the coordination sphere of the latter resulting the formation of excited Eu2+ intermediate (λem = 458 nm) and a neutral azide radical N3•. The activation energy of the light-produced step of the reaction derived from the temperature dependence of the CL intensity growth is 80 kJ/mol.