We investigated activation of thermal dehydriding of alpha-AlH3 crystal by preliminary irradiation by ultraviolet light using thermal desorption spectroscopy, barometry, and cathode luminescence methods. It is shown that hydrogen vacancies appear due to irradiation; they serve as points where metal nuclei probably appear, so dehydriding becomes significantly faster. Possible explanation of transformation of hydrogen vacancies to metal phase nuclei is suggested: new vacancies are more likely to appear near the first one compared to remote places. Using density functional theory method we calculated the electronic structure of stoichiometric alpha-AlH3 and alpha-AlH3 with a hydrogen atom removed from a regular lattice site with a vacancy in place of it. It is suggested that an appearance of a new vacancy near the first vacancy needs less energy compared to the first one. From cathode luminescence data we see that appearance of vacancies can also be activated thermally. The model of hydrogen desorption from alpha-AlH3 activated by UV light is. suggested and kinetic parameters of desorption are evaluated. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.