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 E v is smaller than the energy gap E g and hot valence holes are not able to create any secondary e–h pairs. The E v / E g 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.