Photoproduction of Long-Lived Holes and Electronic Processes in Intrinsic Electric Fields Seen through Photoinduced Absorption and Dichroism in Ca_3Ga_{2-x}Mn_xGe_3O_{12} Garnets

Long-lived photoinduced absorption and dichroism in the Ca_3Ga_{2-x}Mn_xGe_3O_{12} garnets with x < 0.06 were examined versus temperature and pumping intensity. Unusual features of the kinetics of photoinduced phenomena are indicative of the underlying electronic processes. The comparison with the case of Ca_3Mn_2Ge_3O_{12}, explored earlier by the authors, permits one to finally establish the main common mechanisms of photoinduced absorption and dichroism caused by random electric fields of photoproduced charges (hole polarons). The rate of their diffusion and relaxation through recombination is strongly influenced by the same fields, whose large statistical straggling is responsible for a broad continuous set of relaxation components (observed in the relaxation time range from 1 to about 1000 min). For Ca_3Ga_{2-x}Mn_xGe_3O_{12}, the time and temperature dependences of photoinduced absorption and dichroism bear a strong imprint of structure imperfection increasing with x.Comment: 20 pages, 10 figure

Luminescence of lead azide induced by the electron accelerator pulse

Luminescence of lead azide Pb(N3)2 crystals in the range of 400-1000 nm is studied experimentally. As the detonation of lead azide is initiated by an electron accelerator pulse, the onset of the mechanical destruction is preceded by intensive luminescence and a rapid growth of the conductivity. Theoretical investigation of the electronic structure of a lead azide crystal was done by means of the Hartree-Fock method for a periodic system. Detailed comparative analysis of the calculated density of states and experimental luminescence spectrum of lead azide suggests that decomposition proceeds by a chain reaction mechanism. A model of the pre-explosive luminescence based on the hypothesis of the quasi-local state formation in the valence band is proposed. The position of a possible energy level of the state in the valence band is predicted. © 2000 Elsevier Science B.V. All rights reserved

Role of electronic excitations in explosive decomposition of solids

A combined theoretical and experimental study is performed for the initiation of chemistry process in high explosive crystals from a solid-state physics viewpoint. In particular, we were looking for the relationship between the defect-induced deformation of the electronic structure of solids, electronic excitations, and chemical reactions under shock conditions. Band structure calculations by means of the Hartree-Fock method with correlation corrections were done to model an effect of a strong compression induced by a shock/impact wave on the crystals with and without edge dislocations. Based on the obtained results, an excitonic mechanism of the earliest stages for initiation of high explosive solids is suggested with application to cyclotrimethylene trinitramine (also known as RDX) crystal. Experimental tests of this mechanism for AgN3 decomposition controlled by the dislocation density were worked out. The use of pulse radiolysis techniques allows us to observe pre-explosion modifications in properties and behavior of the solids. Pre-explosion conductivity and pre-explosion luminescence measurements for a series of heavy metal azides lead us to the model for the development of the decomposition chain reaction. Thus, the key role of electronic excitations facilitated by edge dislocations in explosive solids is established and analyzed. Practical applications of the suggested mechanisms are discussed. © 2001 American Institute of Physics