An erbium and ytterbium co-doped tantalum-oxide (Ta2O5:Er, Yb) thin film was fabricated using a simple co-sputtering method for the first time, and its photoluminescence (PL) spectrum was evaluated. Energy transfers between Er 3+ and Yb 3+ in the Ta2O5:Er, Yb co-sputtered thin film were discussed by comparing between PL spectra of the Ta2O5:Er, Yb film and Ta2O5:Er or Ta2O5:Yb films reported in our previous works. Such a Ta2O5:Er, Yb co-sputtered film can be used as a high-refractive-index and light-emitting material of a multilayered photonic crystal that can be applied to a novel light-emitting device, and it will also be used as a multi-functional coating film having both anti-reflection and down-conversion effects for realizing a high-efficiency silicon solar cell.