Thermally induced optical scintillations from single crystals of unirradiated BeO:Li and BeO:Na

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Abstract
Optical scintillations from single crystals of BeO:Li and BeO:Na have been observed in the temperature interval 15-575 K. These scintillations result from subjecting the crystals to a temperature ramp and do not require previous irradiation. It is suggested that pyroelectricity forms the basis for adequately explaining this phenomenon. The electric field near the surface is related to the surface temperature gradient by E = (λTd/KεQ) ΔT/Δ X, where λT is the pyroelectric coefficient, d is the charge-separation distance, and x is the dielectric constant. For small changes in ΔT/Δ X (perhaps as small as 0.26 K/mm), an electric field of sufficient magnitude to break down air is produced. The optical spectrum of these scintillations corresponds to the second positive system of molecular nitrogen. It is shown that there exists a correlation between the temperature region of maximum scintillation activity and the temperature region where an anomalous heat capacity is observed in these samples.