The green up-conversion (UC) behavior was observed in a new phosphor Y6W2O15:Er3+. Taking the concentration quenching and sensitization effect into consideration, we obtained the optimized phosphor Y5.86W2O15:0.05Yb3+,0.09Er3+. With the adhesion of Y5.86W2O15:0.05Yb3+,0.09Er3+ phosphor layer, the spectral response was first observed in a 973-nm laser-driven GaAs solar cell. A maximum output power of 0.339 μW was measured using a 300-μm UC phosphor layer on illumination with a 973-nm laser at 145.65 W/cm2. These results verified the UC effect of the Y5.86W2O15:0.05Yb3+,0.09Er3+ phosphor synthesized herein.