This paper reports on the effects of Li þ , Na þ , Mg 2þ , Ca 2þ , Sr 2þ , and Ba 2þ co-doping on the scintillation properties of LaBr 3 :5%Ce 3þ . Pulse-height spectra of various gamma and X-ray sources with energies from 8 keV to 1.33 MeV were measured from which the values of light yield and energy resolution were derived. Sr 2þ and Ca 2þ co-doped crystals showed excellent energy resolution as compared to standard LaBr 3 :Ce. The proportionality of the scintillation response to gamma and X-rays of Ca 2þ , Sr 2þ , and Ba 2þ co-doped samples also considerably improves. The effects of the co-dopants on emission spectra, decay time, and temperature stability of the light yield were studied. Multiple thermoluminescence glow peaks, decrease of the light yield at temperatures below 295 K, and additional long scintillation decay components were observed and related to charge carrier traps appearing in LaBr 3 :Ce 3þ with Ca 2þ , Sr 2þ , and Ba 2þ co-doping.