Pr 3+ -doped Lu 3−x Sc x Al 5 O 12 and Lu 3−x In x Al 5 O 12 (x=0, 0.025, 0.1, 0.25, 0.5, 0.75, 1, and 2) polycrystals are fabricated by the high-temperature solid state reaction method. Although X-ray excited luminescence measurements show that there is no positive contribution of Sc 3+ or In 3+ substitution on the scintillation efficiency, but the physical aspects of band-gap engineering such as the cooperative process of excitation and thermal ionization of 5d 1 excited state are illustrated in this study. We employ a combination of optical diffuse reflectance, photoluminescence, decay kinetic, thermoluminescence experiments to reveal the influence of Sc 3+ or In 3+ substitution on electronic structure and luminescent properties in Pr 3+ -doped lutetium aluminate garnet.