Degassing and diffusion characteristics of Eu-doped gahnite ZnAl2O4 by kinetic thermodesorption mass spectrometry

Abstract

The content of water and other gases in crystalline europium-doped zinc aluminate (ZnAl2O4:Eu3+) synthesized in a supercritical water fluid, the temperature regions of their maximum release during vacuum heat treatment, their degassing, kinetic and diffusion characteristics were determined by the kinetic thermodesorption mass spectrometry for the first time. Water and carbon-containing substances (CO2, CO, hydrocarbons CxHy) are the main volatile impurities in ZnAl2O4:Eu3+ crystals. The release of hydrogen and oxygen indicates very complex redox processes in ZnAl2O4:Eu3+ with the participation of vacancy structures and crystal lattice defects. A decrease in the water diffusion coefficients in aluminate materials correlates with an increase in their density. The obtained diffusive characteristics make it possible to calculate the time of material degassing to the required level. Knowledge of the real defectiveness of ZnAl2O4:Eu3+ crystals in relation to the content of water and other gases can be useful in working out the modes of crystal sintering in order to obtain transparent luminescent ceramics.