Influence of Ca2+ and Zr4+ codoping on the optical characteristics of Gd3Al2Ga3O12:Ce single-crystal

Scintillation materials that can convert absorbed high-energy particles into photons of visible radiation find many applications, in particular in modern methods of medical imaging. Gd3Al2Ga3O12 : Ce is promising single crystal for use as a detecting crystal element of the positron emission tomographs due to its unique properties: high density, high light output, radiation hardness, etc. However, its scintillation kinetics currently limit the use of this crystal. Changing of these kinetics by codoping becomes a priority task, which is considered in many papers. The literature data analysis showed that the optical characteristics of such codoped crystals were not well enough studied or were not investigated at all. In this regard, the spectral dependences of transmission, absorption and reflection are measured using optical spectroscopy for Gd3Al2Ga3O12:Ce, Gd3Al2Ga3O12 : Ce,Ca and Gd3Al2Ga3O12 : Ce,Zr. Dispersion dependences of refractive in dices are obtained by approximating the refractive indices measured using the Brewster method. The approximation was carried out using the Cauchy equation. The material constants of this equation are estimated.

MATERIAL ELEMENT MODEL AND THE GEOMETRY OF THE ENTROPY FORM

In this work we analyze and compare the model of the material (elastic) element and the entropy form developed by Coleman and Owen with that one obtained by localizing the balance equations of the continuum thermodynamics. This comparison allows one to determine the relation between the entropy function S of Coleman–Owen and that one imported from the continuum thermodynamics. We introduce the Extended Thermodynamical Phase Space (ETPS) [Formula: see text] and realize the energy and entropy balance expressions as 1-forms in this space. This allows us to realizes I and II laws of thermodynamics as conditions on these forms. We study the integrability (closure) conditions of the entropy form for the model of thermoelastic element and for the deformable ferroelectric crystal element. In both cases closure conditions are used to rewrite the dynamical system of the model in term of the entropy form potential and to determine the constitutive relations among the dynamical variables of the model. In a related study (to be published) these results will be used for the formulation of the dynamical model of a material element in the contact thermodynamical phase space of Caratheodory and Hermann similar to that of homogeneous thermodynamics.