Polymorphic phase transitions and recombination luminescence in ammonium halide crystals

Abstract

Spectral-luminescent properties of ammonium halide crystals were studied in this work. The propertiesof the peak of thermally stimulated luminescence (TSL) in the region of the phase transition temperaturewere studied and the basic laws were established. A sequential thermal annealing isolated the TSL peakwith a maximum at 240 K for ammonium chloride activated with rare-earth ions (RI). It was found that anorder-disorder phase transition occurs for activated RI of ammonium chloride at a temperature of 240 K. Anappearance of TSL peak with a maximum at 240 K causes because of exposure to ionizing radiation uponactivation of ammonium halides by thallium and tin ions. This phenomenon is observed when ammoniumhalides are activated by europium, ytterbium, neodymium, praseodymium, copper, cadmium and potassiumions. The introduction of impurity homologous anions into the crystal lattice does not give a similar effect.Therefore, it can be argued that observed phenomenon is associated with the presence of impurities in thecationic sublattice and its appearance does not depend on the parameters of the impurity center. On the onehand, the TSL peak is not impurity, since its position is determined by the properties of matrix and on theother hand, its appearance is associated only with substitution ions in the cationic sublattice. The obtainedresults allow studying the crystals response under exposition to ionizing radiation.