In the present study, white light emission based on both upconversion and thermal processes from single-phase yttrium silicate nanopowder doped with Neodymium (III) (Nd3+) was investigated at both room pressure and vacuum (0.01 mbar) with a diode laser excitation of 808 nm. 1% Nd3+ doped (per mole) yttrium silicate (Y2O3:SiO2) nanopowder was synthesized by using the sol-gel method and annealed at 1250 degrees C for 12 h to obtain the powder form. Emission for upconverted white light mainly due to the transitions of Nd3+ ions was obtained below similar to 5.79 W of the laser beam power at atmospheric pressure. For powers exceeding similar to 5.79 W, the powder emitted a thermal white light (WL) due to the photon avalanche mechanism together with thermal processes. The threshold power to obtain thermal white light with the transitions of Nd3+ ions was decreased to similar to 3.51 W at the vacuum condition. These processes were investigated in detail by studying the spectral differences of the rise and decay patterns at atmospheric pressure and vacuum conditions.