Deciphering the Mechanism of Enhanced Scintillation Properties in In-doped β-Ga₂O₃ Ultrafast Scintillation Crystal

β-Ga₂O₃ is a promising ultrafast semiconductor scintillator, but its efficiency is hindered by low light yield and slow decay components. Here, high-quality β-Ga₂O₃:In single crystals were grown by the optical floating-zone method. In3+ incorporation narrows the bandgap (4.76 eV to 4.72 eV), redshifts photoluminescence, strengthens electron–phonon coupling, and accelerates recombination, with a 91 meV activation energy for blue-to-ultraviolet energy transfer. Compared to unintentionally doped (UID) β-Ga₂O₃, the β-Ga₂O₃:In bulk single crystal demonstrates enhanced light yields of (3348 ± 310) ph/MeV and (5664 ± 710) ph/5.5 MeV under 662 keV γ-ray and 5.5 MeV α-ray excitation, respectively, using Bi4Ge3O12 (BGO) as the reference scintillator, together with a markedly faster nanosecond-scale decay. The improved performance is attributed to enhanced charge transport and carrier recombination, highlighting its potential for ultrafast radiation detection.