LiBaPO:Eu phosphor and Ag-coated LiBaPO:Eu composites (Ag/LiBaPO:Eu) were prepared via solid-state reaction and traditional photoreduction methods, respectively. The samples were characterized via XRD, SEM, and UV-vis optical absorption spectroscopy. Two photoenergy conversion processes, namely, photocatalysis and photoluminescence, were investigated in detail. In comparison with as-prepared LiBaPO:Eu phosphor, Ag-modified composites exhibited the enhanced photocatalytic effects together with the quenched Eu luminescence. A Schottky barrier was created on the interface between Ag nanoparticles and LiBaPO host, thereby greatly delaying the recombination between the light-induced holes and electrons. A photoenergy conversion mechanism was suggested and discussed on the basis of the experiments. The Eu ion luminescence centers directly participated in the photodegradation with the meditation of Ag nanoparticles on the surface. With the increase of the Ag coating level on the surfaces, some emission peaks corresponding to D → F transitions of Eu ions were detected. Eu/Eu couples also play an important role in improving photocatalysis. LiBaPO:Eu phosphor is a good candidate for the investigation of multimodal photoenergies of photoluminescence and photocatalysis.