Nanoscale physics

EPR study of nanosized fumed silica incorporated with aged Zn(acac)2 ethanol solution
Savchenko D.V.1,2, Memon V.S.1, Kuz O.P.1, Vasin A.V.1,3, 
Kysil D.V.3, Rusavsky A.V.1,3, Nazarov A.N.1,3,  Kalabukhova E.N.3
1 National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute”, Prospect Peremohy, 37, Kyiv, 03056, Ukraine. 
E-mail: dariyasavchenko@gmail.com
2 Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Prague, Czech Republic.
3 V.E. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, Prospect Nauky 41, Kyiv, 03028, Ukraine.

Recently it was reported about the intense photoluminescence (PL) of zinc acetylacetonate (Zn(acac)2) solution in ethanol after exposing period of several months in laboratory conditions [1]. It was supposed that one of the possible aggregates responsible for the intense PL in Zn(acac)2 solution could be carbon (C) clusters/nanoprecipitates that can be formed as byproduct of Zn(acac)2 hydrolysis. For the detailed study of these centers by electron paramagnetic resonance (EPR) technique, we have infiltrated the fumed silica (S~295 m2/g, d~10-12 nm) with Zn(acac)2 solution of different concentration (1 wt.% and 4 wt.%). As a result SiO2:C nanocomposites were obtained. The samples were annealed in the air at 600ºC. In the SiO2:C nanocomposites infiltrated with 1% of Zn(acac)2 no EPR spectra were observed. After thermal annealing of those samples at 600ºC we have detected a weak single Lorentzian EPR signal. In the SiO2:C nanocomposites infiltrated with 4 wt.% of Zn(acac)2 a weak single Lorentzian EPR signal was observed, while the thermal annealing at 600ºC doubles its spin concentration. The observed single Lorentzian line in both types of the samples is the same and is characterized by g = 2.0042(3) and EPR linewidth ~0.5 mT. We attribute this line to oxygen-centered carbon radical in the sp3-hybridized state. Thus, we confirm the suggestion that intense PL observed previously in Zn(acac)2) solution can be associated with carbon-related nanoclusters. 
The work was supported by MES of Ukraine (Project F2211), Projects No. CZ.02.1.01/0.0/0.0/16_013/0001406, LM2015088 and LO1409 (MEYS CR).

1.	A.V. Vasin, D.V. Kysil, G.Yu. Rudko, et.al. Visible photoluminescence of aged Zn(acac)2/C2H5OH solution: emission/excitation/kinetics study // Proc. of NANO-2017, 23-26 August, Chernivtsi (2017). P. 338.