We estimated the temperature of the gas phase surrounding a Y2O3 sample melted at the focus of a solar furnace by comparing the fluorescence spectra of YO molecule A2 Π 1/2-X2 Σ +, A2 Π 3/2-X2 Σ +, B2 Σ +-X2 Σ + systems and simulated spectra (two temperature model). If A3/2 and B systems can be described by a simple formulation for the calculation of upper and lower states energies, we have had, despite the poor resolution of our instrument, to use a full formulation and particularly introduce the Λ doubling terms, to satisfactorily describe the A1/2 system. At low pressure the discrepancies between rotational and vibrational temperatures and the weakness of the fits suggest that the populations of internal levels do not follow Boltzmann distributions mainly close to the vaporizing surface. The temperatures determined at higher pressures (50 hPa) on the three systems are consistent each others and supposed representative of that of the gas phase.