The luminescence properties of YPO4 phosphors activated with 2% Sm3+ and variable concentrations of Bi3+ (from 0 to 5%) have been investigated. Steady state emission and decay time measurements clearly evidence an increment of the emission performance as the Bi3+ content increases up to 2.5%. Quantum yield measurements provide quantitative confirmation of the experimental observations. This behavior has been associated to the effect of the Bi3+ ions on the optical properties of the host lattice.