Luminescence of high-temperature single-crystal superconductors cleaved in ultrahigh vacuum

Homogeneity assessment of YBa2Cu3O7−x single crystals by cathodoluminescence microscopy

“…In our case the spectrum extents to lower energies showing significative intensity up to 2 eV instead of the 2.5 eV energy which appears as an approximate limit in Ref. 15. The CL spectrum of this work includes a component at about 2.3 eV, resolved in the spectra of localized areas.…”

“…Another intrinsic luminescence band centered at about 2.85 eV has been investigated by different authors by CL and photoluminescence ͑PL͒ in Bi-and Y-based superconductors. Fugol et al 14 attribute the 2.85 eV emission to electron transitions due to a charge transfer process involving an F center and a negative molecular oxygen ion, and Stankevitch et al 15 consider the possibility of an oxygen quasimolecule as the center responsible of the 2.85 eV luminescence that they observed in YBa 2 Cu 3 O 7Ϫx and Bi 2 Sr 2 CaCu 2 O 8ϩx single crystals. Although the different reports show the similarity of luminescence spectra of ceramic samples and single crystals, the information obtained by CL microscopy refers mainly to ceramics samples.…”

Cathodoluminescence microscopy of superconducting and non-superconducting Tl2Ba2CuO6+δ polycrystals

“…Refs. [8] and [10], also involve processes with oxygen atoms or oxygen vacancies. For these reasons, the possibility that features in the oxygen sublattice determine or influence the spectral response of the different samples used in this work is considered here.…”

“…The luminescence emission of samples without postpreparation treatment is in general weak and the 430 nm bands dominate the spectra. This band is considered to be intrinsic to the abovementioned HTSC systems and has been attributed in the case of YBCO and BSCCO to an oxygen quasimolecule [8] or to a complex involving F center and negative molecular oxygen ion in YBCO [10]. The band has been also observed in TBCO samples prepared under high pressure at high temperature [11].…”

“…Investigations of ceramic or crystalline samples of YBa 2 Cu 3 0 7 -x (YBCO), Bi 2 Sr 2 CaCu 2 0 x (BSCCO) and Tl 2 Ba 2 CuO 6+x (TBCO) have revealed similar luminescence spectral features suggesting that the emission bands are related to structural properties, as the existence of Cu-O planes, common to the mentioned materials. Visible luminescence has been mainly observed in the blue-green spectral range [1][2][3][4][5][6][7][8][9][10][11][12] often showing well resolved bands peaked at about 430 nm (2.9 eV) and 540 nm (2.3 eV). The luminescence emission of samples without postpreparation treatment is in general weak and the 430 nm bands dominate the spectra.…”