The objective of this study is the validation and improvement of thermochemical models used in simulations of combustions such as deflagrations and detonations. The validation is done on explosives containing aluminum particles, which oxidizes into alumina during the combustion. One of the objectives is to study the thermochemical states of alumina in the deflagrations of hybrid gas/particle mixtures of H2/O2/CO2/N2 and aluminum particles. In order to do so, alumina's volume fraction, size and temperature have to be determined in different thermodynamic conditions. These information are obtained by measuring the radiance of alumina by spectroscopic means in the visible and near infrared wavelength regions. In this work, our aim is to utilize the visible and near infrared ranges where the radiance of alumina is less affected by other parameters such as the emission of the other species. The optimal wavelengths are determined by analyzing the radiance's sensitivity to the searched parameters. The evolution of the spectra is studied in ranges up to 3600 K and 21 bar, in the visible and near infrared regions. They are compared with the spectra of the same gas mixtures without aluminum particles, all things being equal. This preliminary work will provide information on the optimal wavelength ranges suitable to measure accurately the radiance of alumina, and in further works determine the volume fraction, the temperature and size of alumina particles in deflagrations.