Abstract As a booming semiconductor material, β -Ga 2 O 3 with an ultra-wide bandgap of 4.8 eV exhibits several advantages in scintillators including high stability and low self-absorption. To further improve the scintillator performance, we grew unintentionally doped, Cu-, Fe-, Mg-, and Si-doped β -Ga 2 O 3 substrates using the floating zone method. The 0.1 mol% Cu-doped β -Ga 2 O 3 exhibits the highest light yield of 6957 ph MeV −1 with a good linear response, which represents better predictability and stability for the input x-ray energy. Photoluminescence shows peak emission around 425 nm under the excitation of 254 nm. All the results show that Cu-doped β -Ga 2 O 3 makes an effective scintillator with excellent light yield, and is an alternative for the high-performance ionizing radiation detectors.