Abstract:Luminescence dating was applied to four Neolithic pottery fragments excavated at Lumea Nouă (Alba Iulia, Romania), with the purpose of improving the chronology for the archaeological finds, and hence, the occupational history of the site. The single-aliquot regenerative-dose (SAR) protocol was applied to both blue and infrared stimulated luminescence signals from coarse quartz and polymineral fine grains, respectively. A more conventional approach which uses a multiple-aliquot additive-dose protocol and thermoluminescence signals from polymineral fine grains was applied as well. The characteristics of the OSL and IRSL signals were investigated in terms of behaviour in the SAR protocol, dose response and dose recovery. Additionally, anomalous fading measurements of the 410 nm IRSL emission and of the blue TL emission from polymineral fine-grains were performed. Both signals were observed to be affected by anomalous fading. OSL dating of quartz using the SAR protocol is considered to be the technique of choice; it yields an average age of 6.0±0.4 ka (n = 4), which is in agreement with archaeological expectations. The dating results allow refining the typological interpretation of the objects and improve the chronological framework for the site.
Phase-change memory materials are promising for the next generation of non-volatile flash memory that will serve in new mobile computing entertainment and other handheld electronics. Among them are chalcogenide glasses Ge-Sb-Te (GST) which can exist in two separate structural states -amorphous and crystalline. Switching of the material from one to another state can be done by heating applying an electrical pulse or by exposure to intense laser beam. In the present work we report the changes of optical parameters of amorphous Ge 1 Sb 2 Te 4 , Ge 1 Sb 4 Te 7 , and Ge 2 Sb 2 Te 5 thin films under heat treatment and light exposure. The illumination with white during 1 hour does not change the transmission spectra of the as-deposited amorphous film. The spot of phase change transformation of the amorphous material was observed when the film was illuminated with UV laser pulses. From the transmission spectra T=f(λ) the optical constants (Absorption coefficient α, optical band gap E g , refractive index n, the average electronic energy gap E 0 and the dielectric oscillator strength E d were calculated. For Ge 1 Sb 2 Te 4 the value of E 0 is smaller than optical band gap E g =1.08 eV obtained from the Tauc plot. Large values of the refractive index n are obtained for smaller E 0 =0.931 eV and for large E d =7.448 eV. The anealing of the amorphous Ge 2 Sb 2 Te 5 thin film at T=100 o C during t=4 min shifts the transmission spectra in the low frequency region. The anealing at higher temperatures makes the thin film non-transparent, e.g. take place the process of crystalization.
The optical properties of amorphous Ge x As x Se 2-x (x=0.05÷0.30) thin films prepared by thermal evaporation on the glass substrates held at T substr =100 o C are reported. The transmission spectra was used for calculation of the absorption coefficient α, optical band gap E g , and the values of the refractive index n. The dependences of α, E g , and n on the film composition in the Ge x As x Se 2-x glassy system were determined. It was established that the optical band gap E g decreases, while the refractive index n increases with the increasing of the concentration of Ge and As in the Ge x As x Se 2-x glassy system. The time dependence of the transmission T(t) during the light exposure for the above band gap illumination (photodarkening) is described by a strength exponential behaviour T(t)/T(0) = A 0 +Aexp[-(t-t 0 )/τ] (1-β) , where t is the exposure time, τ is the apparent time constant, A characterizes the exponent amplitude, t 0 and A 0 are the initial coordinates, and β is the dispersion parameter (0<β<1).
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