title: Formation of carbon nanodots with different spin states in mechanically processed mixtures of ZnO with carbon nanoparticles: an electron paramagnetic resonance study.
abstract: Mixtures of zinc oxide with carbon nanoparticles, ZnO + xC (x = 0.1%, 1% and 3% by weight), were subjected to mechanical processing (MP) in a hermetically sealed grinding chamber. Using electron paramagnetic resonance (EPR) spectroscopy, we monitored the evolution of spin centers in CNPs. While the initial CNPs were EPR silent, their short-duration MP (tMP) gave rise to emergence of low-intensity carbon signal. Increasing the sample temperature at tMP> 9 min induced CNP oxidation, which lead to a dramatic increase in the intensity of C signal. The oxidation process also manifested itself in the appearance of a photoluminescence (PL) band at ∼2.8 eV, which is characteristic for carbon nanodots with an average size of ∼2.7 nm. A limited amount of oxygen in the grinding chamber lead to different ways of carbon nanodot oxidation, depending on carbon content in the samples, which in turn influenced the characteristics of C EPR signals observed. The number of spins calculated per one CNP (NSOP) was found to depend on carbon content in ZnO + xC samples. Based on a detailed analysis of EPR spectral lines, we suggest the existence of a broad variety of relaxation mechanisms for forming C paramagnetic centers.
authors.affiliation: Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, 62210 Cuernavaca, Morelos, Mexico. kakazey@hotmail.com.
authors.forename: M
authors.identifier: http://orcid.org/0000-0002-8469-3881
authors.initials: M
authors.lastname: Kakazey
authors.affiliation: Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, 62210 Cuernavaca, Morelos, Mexico. kakazey@hotmail.com.
authors.forename: M
authors.initials: M
authors.lastname: Vlasova
authors.affiliation: Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior C.U., 04510 Cd. México, Mexico.
authors.forename: V
authors.initials: V
authors.lastname: Gómez-Vidales
authors.affiliation: Laboratorio Avanzado de Nanoscopía Electrónica (LANE), Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, (CINVESTAV), Zacatenco, 07360 Cd. México, Mexico.
authors.forename: A
authors.initials: A
authors.lastname: Ángeles-Pascual
authors.affiliation: Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Circuito Exterior C.U., 04510 Cd. México, Mexico.
authors.forename: V A
authors.initials: VA
authors.lastname: Basiuk