Intrinsic Luminescence from Li2O Crystals Excited in the Exciton-Band Region

Abstract

Photoluminescence of lithium oxide (Li2O) has been studied under the excitation with UV light in the fundamental absorption region at low temperatures. Two bands appear at 3.70 and 4.75 eV. The 3.70 and 4.75 eV bands are stimulated on the low‐ and high‐energy sides of the exciton reflection band peaking at 7.02 eV, respectively. An interesting fact is that there appears no luminescence under the above‐gap excitation. The 4.75 eV band is ascribed to radiative decay of self‐trapped excitons, and the 3.70 eV band is related to unavoidably existing defects or impurities. Both a broadening of the line width and a quenching of the intensity of the 4.75 eV band are also investigated in the temperature range 9 to 300 K. The present result is discussed in comparison with the theoretical model of the self‐trapped exciton in this material.

The ionic conductivity in lithium-boron oxide materials and its relation to structural, electronic and defect properties: insights from theory

“…The obtained transition energy is in good agreement with the experimental value of 3.7 eV [29], whereas the PW91-PAW approach gives too small a value of the optical absorption energy, namely 2.7 eV. This can be related to the artificial self-interaction in DFT methods which is not completely removed in the GGA.…”

“…In that study the displacements were even smaller, namely by 0. The experimental value of the optical transition energy for oxygen deficient Li 2 O is 3.7 eV [29], indicating a location of a doubly occupied defect level about 4.3 eV above the valence-band-maximum (VBM). This is reflected by the calculated density of states (DOS) of the defective supercells.…”

“…Schottky disorder is also observed, but it is not as predominant as the cation Frenkel defect [34]. On the other hand, the dominant irradiation defects in Li 2 O are known as F centres [29,36,37] and F + centres [29-31, 38, 41, 42]. In a combined experimental and theoretical study of defects in Li 2 O, Chadwick et al [34] showed that Li + ions migrate via cation vacancies.…”

Low-temperature irradiation effects in lithium orthosilicates

“…in the region of the efficient excitation of 5-eV emission [20]. In Li 2 O single crystals at 9 K, two emission bands at 3.7 eV (hm exc = 6.8 eV) and 4.75 eV (hm exc = 7.7 eV) [11], as well as the 4-eV absorption band related to the so-called F + centers (an electron in the field of an anion vacancy) [9,10] have been revealed. One might expect the analogous emissions of STEs, F and F + centers in Li 4 SiO 4 ceramics as well.…”

“…A Li 4 SiO 4 complex compound consists of SiO 4 tetrahedrons and small-radius Li atoms bonded to the oxygen atoms. The results of long-standing investigations of the physical processes in a-SiO 2 crystals and other silicates [6][7][8], as well as in Li 2 O single crystals and ceramics [9][10][11][12], will be useful for the study of lithium orthosilicates. The main applications of Li 4 SiO 4 ceramics are expected at temperatures close to the melting point (1230°C) of the material.…”