Transparent Ceramics Research Center, SICCAS
Key Laboratory of Transparent Opto-fuctional Inorganic Materials, CAS
Delayed recombination: thermal ionization, quantum tunneling and bent bands
Dr. Eva Mihokova
Institute of Physics, Czech Academy of Sciences, Prague, Czech Republic
Abstract: To improve the performance of a scintillating material it is crucial to understand the physical processes involved in the scintillation mechanism. We focus on several processes and phenomena that can affect the amount of scintillation light the certain material can produce. These are, in particular, thermal ionization of the activator’s excited state, quantum tunneling between the activator and nearby trap and local changes of band structure caused by the presence of an activator. All these phenomena can be studied by the so called delayed recombination decay technique.
The technique was developed in our optical lab and it is based on monitoring the slow components of the activator’s decay when it is selectively excited into its lowest absorption band. We show examples of experimental observation of delayed recombination decay as well as the model of its temperature dependence that allows to determine the thermal ionization energy of an activator. We also show how the technique can reveal the presence of quantum tunneling between the activator and nearby trap and associated model whose combination with experimental data enables to assess the trap-activator distance. Based on suggestion from the literature some observed luminescence characteristics could be explained considering the local changes of the band structure, namely the valence and conduction band bending due to the presence of an activator. We used a simple model to confirm such a possibility and show the shift of the conduction band edge into higher energies around the activator (impurity). In other words the meaning of bend bending is that there are fewer electron states near the impurity and they start at higher energies.
Dr. Eva Mihokova is a leading senior scientist in the Institute of Physics, Czech Academy of Sciences in Prague Czech Republic. She studied at the faculty of Mathematics and Physics of the Charles University in Prague, Czech Republic where she received her Master degree. She received her PhD degree in the Institute of Physics Czech Academy of Sciences in Prague Czech Republic. In last years, Eva Mihokova studies optical properties of scintillating materials with wide spectrum of applications. Her research focuses on processes related to luminescence and scintillation mechanisms, their interpretation and numerical modelling. Within methods of characterization of material systems in the form of single crystals, nanopowders and nanocomposites she specializes particularly in investigation of defects and trapping centers by thermally stimulated luminescence technique.
She is an author and coauthor of about 200 scientific papers in international peer-reviewed journals and 1 book chapter. Her publications received more than 3700 citations (excluding selfcitations), H index 33. She was a principal investigator in about 10 domestic and international projects and a research team member in about other twenty. She was awarded the Prize of Academy of sciences of the Czech Republic for excellent scientific results, “PbWO4 single crystals- scintillator for high energy physics. Physical description and material optimization” and The Prize of “Otto Wichterle” of the Academy of Sciences of the Czech republic.