Browsing by Author "Kostova, Irena"

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    Effects of temperature on the time responses of strontium aluminates
    (Elsevier, 2021) Fouzar, Samia; Eftimov, Tinko; Kostova, Irena; Benmounah, Abdelbaki; Lakhssassi, Ahmed
    In this paper we study the effect of temperature on the rise and decay time responses of Eu and Eu, Dy doped strontium aluminates. Normalized switch on and switch off time responses are used to estimate the share of phosphorescence in the observed luminescence. The parameters of the power law time responses related to the relative share of phosphorescence in luminescence and to the rise/decay rates are found to be strongly temperature dependent. The results show that unlike luminescence intensity, the overall efficiency of phosphorescence increases strongly with temperature and reaches a maximum around 65 °C. Thе maximum correlates with the activation energy of the samples and depends on their doping and fabrication technology
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    Excitation and spectral dependence of the rise and decay time responses of Eu2+- and Dy3+-doped strontium aluminates
    (Springer, 2022) Fouzar, Samia; Kostova, Irena; Eftimov, Tinko; Benmounah, Abdelbaki; Ouchabane, Mohammed; Lakhssassi, Ahmed
    In this paper, we study the phosphorescence rise and decay time responses of Eu2+- and Dy3+-doped strontium aluminates prepared by different methods after scanning them with a narrow spectral width (15 nm FWHM) light from a monochromator. The experiments performed show that the time responses essentially depend on the excitation duration as well as on the excitation and the emission wavelengths. It has been found that at the excitation wavelength of maximum efficiency λ′max, a ‘fast track’ rise and decay of the phosphorescence exists. We suggest that by studying the normalized switch on and switch off time responses, we can determine the relative share of slow phosphorescence afterglow with respect to fast and slow phosphorescence decay as well as the rate of luminescence rise and decay processes. The relation to the synthesis technology and to the contents of the samples is discussed
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    A Simple fiber optic temperature sensor for fire detection in hazardous environment based on differential time rise/decay phosphorescence response
    (IEEE, 2022) Fouzar, Samia; Bulgaria, Plovdiv; Kostova, Irena; Dimitrova, Todorka L.; Benmounah, Abdelbaki
    — In the present article, we report the development of a simple temperature sensor based on the difference in the temperature dependences of the rise and decay time and the intensity responses of Eu2+, Dy3+-doped strontium aluminates. A 374-nm pulsed LED was used as a UV source in combination with a lead-in and -out optical fiber to excite the sample and capture the phosphorescence. We show that because of the power law rise and decay time responses, the differential signals measured at earlier instants exhibit the highest sensitivities to temperature over the range from about 5 ◦C to 95 ◦C. Normalized differential signals are characterized by a wide range of linear responses to temperature changes, sensitivity of up to ≈−1.89%/◦C, and a relative error of less than 0.5%. Application to fire prevention is discussed and argumented