Search

Thermally stimulated luminescence (TSL) measurements were conducted both on bare substrates and on high-temperature superconducting (HTS) films deposited onto representative substrates, to demonstrate that TSL is applicable to HTS films in detecting the presence of secondary insulating impurities (for example Y 2 O 3 , BaCO 3 , Y 2 BaCuO 5 , BaCuO 2 ). To provide basic information for this particular application we also report TSL glow curves of the frequently used single-crystal substrates Al 2 O 3 , MgO, YSZ, SrTiO 3 , LaAlO 3 , and LaGaO 3 . Analyses of the well-defined glow peaks yield TSL parameters which suggest that the detrapping of an electron or hole from its metastable state and its subsequent recombination produces luminescence that follows a mixed-order kinetic process (1 ⩽ l ⩽ 2). The thermal activation energy required in this process varies between 0.6 and 2.3 eV and the frequency factor ranges from 10 7 to 10 17 s −1 . Although the luminescence mechanisms in these substrates could not be elucidated with the TSL data alone, these results are found to be adequate for ascertaining the presence of insulating impurities in the HTS films by comparing the TSL of the film-on-substrate and the substrate.

It was recognized shortly after the discovery of high-temperature superconductors (HTS) that these materials would exhibit thermally stimulated luminescence (TSL) as a manifestation of their granularity and consequent inclusion of insulating material at grain boundaries. The large optical absorption coefficients of these opaque materials implies that TSL emanates from within ∼1 μm of the surface. Therefore, TSL can be used to assess the quality of HTS by detecting the presence of insulating surface impurities, which are, in general, deleterious to technological performance. For example, surface resistance R s is determined by HTS properties within the London penetration depth, which is the region probed by TSL. The presence of insulating surface impurities contributes to the high-frequency losses as manifested by an enhanced R s and is directly correlated with TSL. Therefore, in addition to radiation dosimetry and archaeological dating, TSL can also be applied to HTS research.