Multiplication of electronic excitations and prospects for increasing scintillation efficiency in wide-gap crystals

A comparative analysis of the electron-hole (e-h) excitation mechanism of impurity luminescence has been performed for wide-gap oxides (WGO) and alkali halides crystals (AHC). A low quantum yield of scintillation in WGO with respect to that in AHC is connected with the high value of the average energy needed for the creation of an e-h pair in WGO. In AHC and many WGO, the width of a valence band Ev is smaller than the energy gap Eg and hot valence holes are not able to create any secondary e-h pairs. The Ev/Eg ratio that describes “hole losses” in scintillators is 1.5-2.0 times higher in WGO than in CsI. The scenario of the two-step transformation of an e-h pair or an anion exciton into two emitted photons in α-Al2O3:Mg2+,Ti4+ has been considered.