This paper aims to study the excitation mechanism of Nd3+ ions in Nd-SiOx (x < 2) films. The films were deposited by magnetron co-sputtering followed by a rapid thermal annealing at temperature TA ranging from 600 to 1200 °C. Two different photoluminescence (PL) behaviors have been evidenced in SiOx layers depending on the annealing temperature. For low TA (TA < 1000 °C), the recorded visible PL originates from defects energy levels while for high TA (TA > 1000 °C), the visible emission emanates from recombination of excitons in Si nanoclusters. When doped with Nd3+ ions, the visible PL behaviors of Nd-SiOx films follow the same trends. Nd3+ PL was investigated and its decay rate was analyzed in detail. Depending on the annealing conditions, two types of sensitizers have been evidenced. Finally, maximum Nd3+ PL emission has been achieved at around 750 °C when the number of Nd3+ ions excited by the two types of sensitizers reaches a maximum.