Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals

Abstract

The luminescence of GeO2 rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3eV was observed under N2 laser (337nm). At higher excitation photon energies and X-ray excitation an additional band at 3eV appears in luminescence. The band at 2.3eV possesses intra-center decay time constant about 100μs at 290K and about 200μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses under nitrogen laser, therefore the luminescence of rutile-like crystal and reduced sodium germanate glass was ascribed to oxygen-deficient luminescence center modified by sodium. The band at 2.3eV could be ascribed to triplet–singlet transition of this center, whereas the band at 3eV, possessing decay about 0.2μs, could be ascribed to singlet–singlet transitions. Both bands could be excited in recombination process with decay kinetics determined by traps, when excitation realized by ArF laser or ionizing irradiation with X-ray or electron beam. Another luminescence band at 3.9eV in GeO2 rutile-like crystal was obtained under ArF laser in the range 100–15K. Damaging e-beam irradiation of GeO2 crystal with α-quartz structure induces similar luminescence band.