|Visnyk of the Lviv University. Series Physics
55 (2018) ñ. 78-86
Luminescence of polymer composites with embedded LaF3:Gd nanoparticles
Ò. Ì. Demkiv, L. I. Bulyk, T. S. Malyi, A. D. Zhyshkovych, M. V. Diachuk, V. V. Vistovsky, A. S. Voloshinovskii
The luminescence properties of polymeric films based on polystyrene matrix with embedded LaF3:Gd nanoparticles were studied. In the luminescence spectra of LaF3:Gd nanoparticles with anaverage size of 30 nm the domination of narrow emission band of gadolinium ions with maximum at 312.2 nm corresponding to 6P7/2 \rightarrow8S7/2 emission transition and half width of \sim1 nm was revealed. The intensity of gadolinium luminescence significantly decreases with decreasing nanoparticle size to 5 nm. This gives the reasons to consider the small size LaF3:Gd nanoparticles as non-radiative particles in the absorption range of the scintillation polystyrene matrix. In the luminescence spectra of polystyrene matrix with organic activators n-terfenyl and POPOP and in polystyrene composites with embedded LaF3:Gd nanoparticles two emission bands with maximums at 350 and 420 nm, that correspond to luminescence of polystyrene activators n-terfenyl and POPOP are observed. The emission intensity on polymeric composite with 40 wt.\% embedded LaF3:Gd nanoparticles increases by approximately an order compared the emission intensity of polystyrene scintillator without any embedded nanoparticles. The luminescence decay time constant of composites is estimated as 3 ns, which is typical for polystyrene scintillator without inorganic nanoparticles. The presence of luminescence response for nanocomposite scintillators with embedded LaF3:Gd nanoparticles confirms that the main mechanism of scintillations in them is the excitation of the luminescent polystyrene matrix by electrons. The electrons are emitted from LaF3:Gd nanoparticles under ionization radiation due to photoelectric effect mechanism and have enough energy to escape the nanoparticle volume with the consequent excitation of luminescence of the polystyrene matrix.
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