Fast Intrinsic Emissions of Wide-Gap Oxides Under Electron Irradiation

Abstract

. Da:f~l'k /3, 480/00 Almaty, Ka=akhstan .. 'The emission spectra have been measured in the range of 1.6 -9.0eV under irradiation of wide-gap oxides by single electron pulses (3 ns, 300 kV). A fast ( r < 3 ns) continuous and temperature-independent emission, connected mainly with the transitions of hot holes between the levels of the valence band of oxides, can be separated in these spectra at 300 600 K, when the inertial emissions (5-7 eV) of localized excitations undergo a strong thermal quenching. It is suggested that a drastic decrease of the intensity of this so-called hole intraband luminescence (IBL) in a shortwavelength spectral region is caused by the lowering of the density of states at the edges of the valence band and, therefore, supplies information on the width of an anion valence band £, .. The drastic decrease of the IBL intensity takes place at 6.4-8.6eV in BaMgAiw017• SrAI204, MgAI407, MgO and BeO, that agrees satisfactorily with the values of £,. in these systems obtained by other methods.

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

“…The impurity emission peaked at 4.13 eV has been detected in a NaBr:Ca single crystal, while the emission of Mn 2+ and Eu 2+ centres has been registered in Zn 2 SiO 4 :Mn (see also [8]) and SAM:Eu powders, respectively. Our analysis with consideration of near-surface losses showed that in NaBr, one photon of 19 and 23 eV was able to create two or three e-h pairs, Table 2 Energy gap E g ; width of a valence band E v (in eV) and E v =E g ratio for some WGO [19] and AHC [18] respectively [20]. In Zn 2 SiO 4 :Mn and SAM:Eu, near-surface non-radiative recombinations are practically absent but the absolute QY of luminescence only doubles with the rise of the exciting photon energy from 15 eV up to hn ex ¼ 23 eV: According to Table 2, the parameter of ''hole losses'' in NaBr is E v =E g ¼ 0:48; while E v =E g ¼ 0:9 in SAM, i.e.…”

“…on the basis of a short-wavelength edge of a fast (to1 ns) hole intra-band luminescence, connected with radiative transitions of holes inside the valence band [19]. The spectra of a hole intra-band luminescence have been measured at the excitation of WGO by nanosecond pulses of 300 keV electrons.…”