To make a Mn 2+ -doped red glass phosphor that can be excited with ultraviolet (UV) light of light-emitting diodes (LEDs), 60P 2 O 5 -35ZnO-5Al 2 O 3 -8MnO-xCu 2 O glasses (x = 0-1.00) were prepared by a melt-quenching method at 1200-1400°C for 30-180 minutes in atmospheric air, and the redox of Mn and Cu as well as fluorescence properties were investigated. The Mn 2+ ion was not reduced and oxidized in the melting, quenching, and annealing processes. The valence of Cu in the glasses changed in the order of 0, 1+, and 2+ with the increase in the amount of Cu 2 O and in the melting temperature and time. In this study, a 60P 2 O 5 -35ZnO-5Al 2 O 3 -8MnO-0.10Cu 2 O glass melted at 1250°C for 90 minutes, having the highest Cu + concentration, showed the strongest Mn 2+ red fluorescence under the UV light at 275 nm. This strong Mn 2+ red fluorescence has been caused by the energy transfer from excited Cu + ions to Mn 2+ ions.