Quantum confinement in the electron paramagnetic resonance of transition ions in wide band gap nanomaterials


Acronym: CONFIREP

Type: PNII-IDEA 523/2009

Project Director: Dr. Sergiu Vasile Nistor



     The project aims to evidence the quantum confinement effect in the Electron Paramagnetic Resonance (EPR) spectra of transition ions localized in nanomaterials, as quantum dots formed in II-VI wide band gap semiconductor compounds and dielectrics, and to investigate, on this basis, the atomic scale phenomena associated with quantum confinement, in correlation with the resulting optical and structural properties. .


Main objective


     The main objective of the CONFIREP project is the observation for the first time of the quantum confinement effect in the Electron Paramagnetic Resonance (EPR) spectra of transition ions localized in nanomaterials, as quantum dots formed in II-VI wide band gap semiconductor compounds and dielectrics, and the investigation, on this basis, of the atomic scale phenomena associated with quantum confinement, in correlation with the resulting optical and structural properties.
     Two kinds of quantum dots will be investigated: ZnS nanocrystals stabilized by a protective layer and nano-aggregates of divalent halides formed into dielectric crystals of monovalent halides, both with average dimensions < 2.5 nm, synthesized by original procedures developed by the proposer team and structurally characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM) including high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), as well as by emission and absorption optical spectroscopy. During the preparation the quantum dots will be doped with transition ions 3d (iron group) and 4f (rare earth group), which will act as atomic probes in detecting the local effects of quantum confinement by EPR.
     To ensure the success of the proposed objectives we will use various experimental techniques: multifrequency EPR in the X (9.5 GHz)-, Q (34 GHz)- and W(95 GHz)- microwave bands, multiple resonance techniques (ENDOR-Electron Nuclear Double Resonance and ODMR-Optical Detection of Magnetic Resonance), optical emission and absorption spectroscopy in a wide temperature range (6-400 K) as well as complex theoretical models included in special software for computer simulation and analysis of the EPR data.


Secondary objectives


  1. The synthesis of stable quantum dots based on II-IV wide band gap semiconductor compounds doped with transition ions, structurally and spectroscopically well characterized, with average size < 2.5 nm and a tight distribution of dimensions (standard deviation 0.2 nm). We estimate that at such sizes the quantum confinement effects might become observable in the EPR spectra of certain transitions impurity ions.
  2. Multifrequency and multiple-resonance EPR investigations on the nanomaterials/quantum dots doped with transition ions from both iron (3d) and rare earth (4f) groups to reveal the presence of the quantum confinement effect by comparison with the spectral data of the bulk compounds (single and/or polycrystalline).
  3. The investigation of the influence of the nature and concentration of paramagnetic impurities and of the presence of intrinsic point defects on the quantum confinement effects, with the purpose of investigating the mechanisms at atomic scale by which the quantum confinement effect influences the energy levels structure and electronic wave functions, as well as the dipole-dipole and spin-lattice interaction mechanisms which characterize the energy transfer in and between neighboring quantum dots, or those included into crystalline matrices.
  4. The observation of the quantum confinement effect in the dynamic properties of EPR spectra.

Project coordinator :


National Institute of Materials Physics (NIMP)
105bis Atomistilor str., Bucharest, Magurele, PO Box MG-7, zip code 077125, Romania
Phone: + 40-21-369 0185
Fax: + 40-21-369 0177
Website: http://www.infim.ro



Project Director :


Dr. Vasile Sergiu Nistor, Senior Researcher I
Phone: + 40-21-369 0170 / int. 190
Fax: + 40-21-369 0177
E-mail: snistor@infim.ro


Partner : INCDFM


Personnel: Total 6, of which PhDs 4, PhD students 1 and MSc student 1.


Main equipment :


  1. X band (9.2-9.9 GHz), digital EPR spectrometer, model EMXplus, produced by Bruker BioSpin GmbH with Premium X microwave bridge and accessories for variable temperature measurements in the range 3.8-500 K, with in-situ irradiation, a sensibility of 2.5x109 spins/0.1 mT, stability of 10-8 (frequency and magnetic field) and magnetic field range 0.1-17.5 kGauss.
  2. EPR digital spectrometer, model ELEXYS E-500Q-10 for EPR and ENDOR measurements, produced by Bruker BioSpin GmbH (to be installed in the year 2009), with Q band (35 GHz) microwave bridge model ER 051 Q, with sensibility of 1.6x109 spins/0.1mT, stability of 10-8 and magnetic field range 0.1-17.5 kGauss, with accessories for EPR-ENDOR measurements at variable temperatures in the range 3.8-500 K, with in-situ irradiation.
  3. The investigation of the influence of the nature and concentration of paramagnetic impurities and of the presence of intrinsic point defects on the quantum confinement effects, with the purpose of investigating the mechanisms at atomic scale by which the quantum confinement effect influences the energy levels structure and electronic wave functions, as well as the dipole-dipole and spin-lattice interaction mechanisms which characterize the energy transfer in and between neighboring quantum dots, or those included into crystalline matrices.
  4. Laboratory helium liquefier plant model LHeP18 delivered and installed by Cryomech Co. from USA, procured in the frame of the project PN II no.65/CP/I/2007 (project director dr. S. V. Nistor).
  5. Digital installation for optical emission spectroscopy, with monochromators and Xe/Hg lamps from Oriel and PMT detector, to be used with a closed cycle cryocooler for measurements in the 5-380 K temperature range.
  6. Double beam optical spectrophotometers UV-VIS and IR models SPECORD M70 and SPECORD IR75, respectively, from Carl Zeiss Jena, with optical cryostat for measurements at 78-400 K, in the optical ranges: 190-900 nm and 2.5-25 um, respectively.
  7. Analytical TEM microscope, model JEOL-200CX from JEOL, Japan in 1982, upgraded in 2006-2007 with a high performance CCD camera model Keen View 20 and an EDS system for elemental analysis with electron beam from EumeX Instrumentebau GmbH from FRG.
  8. Laboratory for sample preparation for TEM with specialized equipment for thermal treatments in vacuum and controlled atmosphere, for cutting, polishing, ion milling, vacuum deposition, digital optical microscope for sample inspection, produced in USA and FRG and installed in 2007.
  9. Laboratory for single crystal and nanocrystalline materials preparation with equipments for single crystals growth (Czochralski, Bridgman and flux), equipments for synthesis in the liquid and solid phases and equipment for sample preparation for spectral measurements (cutting, polishing, optical and x-ray orientations).

Scientific and Technological Achievements


     An original synthesis procedure for controlled growth of Mn2+ doped cubic ZnS nanocrystals by chemical reaction in liquid solution in the presence of an organic additive which acts as a growth inhibitor, was developed. The microstructural investigations by XRD and TEM/HRTEM, confirm de formation of small cubic ZnS:Mn nanocrystals, with high crystallinity and 2.0 nm +/- 0.2 nm average size, self-assembled into a mesoporous structure. The ESR and optical (emission) investigations confirmed the localization of the Mn2+ ions at substitutional sites in the ZnS nanocrystals as well as two surface centers. The photoluminescence spectrum associated with the Mn2+ impurity ions, exhibit the largest observed red-shifted peak at 605nm, a property which is atributed to the quantum confinment effect. From the correlated analysis of EPR and microstructural data it is shown that substitutional Mn2+ ions are localised at cation (Zn2+) sites perturbed by an axial crstal field due to the presence of a neighbouring extended planar defect as a twin or stacking fault. Such preferential localisation of Mn2+ impurity ions , which seems to take place in other cubic II-VI semiconductor nanocrystals is explained by a newly prosed mechansim of extended latice defect assited incorporation of impurities. This mechanism can also explain the relatively large concentration of divalent impurity ions (Mn2+, Co2+) observed such materials prepared at relatively low temperatures.


Published Papers


  1. "Incorporationand localisation of substitutional Mn2+ ions in cubic ZnS quantum dots."
    S. V. Nistor, M. Stefan, L. C. Nistor, E. Goovaerts and G. Van Tendeloo
    Physical Review B 81(3) 035336 (6 pp) (2010)
  2. "Improving the cubic ZnS nanocrystals quality by self-assembling into a mezoporous structure."
    S. V. Nistor, L. Nistor, M. Stefan, D. Ghica, C. D. Mateescu and R. Birjega
    Rom. Rept. Phys. 62 (2) 319-328 (2010)

Conferences & Workshops


  1. EPR of transition ions in (nano)crystalline materials (invited lecture)
    S. V. Nistor
    Joint IFIN-HH-ICTP-IAEA Workshop on "Trends in Nanoscience: theory, experiment, technology", August 23-30, 2009, Sibiu, Romania
  2. Localization of Mn2+ impurity ions in cubic ZnS quantum dots (oral presentation)
    S. V. Nistor, M. Stefan, L. C. Nistor and C. D. Mateescu
    Joint IFIN-HH-ICTP-IAEA Workshop on "Trends in nanoscience: theory, experiment, technology", August 23-30, 2009, Sibiu, Romania

Laboratory Networks


     Participation at the Network of 20 specialized ESR laboratories from EU countries financed by ESF, entitled: "Advanced paramagnetic resonance methods in molecular biophysics" - COST P-15 action (2005- 2010); National coordinator for Romania: Dr. S. V. Nistor


International Projects


     Bilateral scientific collaboration entitled: "Designing new advanced, multifunctional materials with lattice defects", (2005-2009), foreign partner: University of Antwerp, ECMP Laboratory, Antwerp, Belgium, Prof. E. Goovaerts. Co-director from the Romanian partner: Dr. S. V. Nistor

Stages Activities Calendar
Stage I Activity 1. The synthesis and characterization of nanocrystalline cubic ZnS (nano ZnS), doped with Mn2+ ions, with average size < 2.5 nm.
Activity 2. Submission and acceptance for publication of a paper in a scientifically recognized international journal ISI indexed.
September 2008
Stage II Activity 1. Synthesis of nanocrystalline cubic ZnS (nanoZnS) with various concentrations of Mn2+ and different average dimensions in the range of 1.8-2.5 nm and a maximum standard deviation of 0.2 nm.
Activity 2. Submission and acceptance for publication of a paper in a scientifically recognized international journal ISI indexed.
December 2009
Stage III Activity 1. Preparation of cubic (blende) ZnS single crystals doped with Mn2+ as reference specimens and accurate determination of the EPR spectra parameters.
Activity 2. Procurement of small scientific equipments, software and materials necessary for performing the activities in the present project.
Activity 3. Participation at international conferences related with the research field of the project, with presentation of original results obtained in the frame of the present project. Research stage for experimental investigations required by the present project.
September 2010
Stage IV Activity 1. Synthesis and characterization of nanoZnS doped with other transition ions (Cu2+, Fe3+, Co2+, Eu2+, Gd3+, ...) with average dimensions < 2.5 nm and maximum standard deviation of 0.2 nm.
Activity 2. Identification of quantum confinement effects in the EPR and/or ENDOR spectra of nanoZnS doped with Mn2+ ions.
Activity 3. Preparation of cubic (blende) ZnS single crystals doped with other (Cu2+, Fe3+, Co2+, Eu2+, Gd3+, ...) transition ions, as reference specimens.
Activity 4. Submission and acceptance for publication of a paper in a scientifically recognized international journal ISI indexed.
December 2010
Stage V Activity 1. Preparation of quantum dots/nano-aggregates doped with Mn2+ ions in cubic alkali halides matrices.
Activity 2. Investigation of the effects of paramagnetic impurities in nanoZnS at various concentrations on the dynamic properties of the EPR spectra.
Activity 3. Procurement of small scientific equipments, software and materials necessary for performing the activities in the present project.
Activity 4. Participation at international conferences related with the research field of the project with presentation of original results obtained in the frame of the present project. Research stage for experimental investigations required by the present project.
September 2011
Stage VI Activity 1. Identification, in the EPR spectra of Mn2+ in PbCl2 nano-aggregates / quantum dots distributed in NaCl or RbCl crystalline matrices, of quantum confinement effects .
Activity 2. Submission and acceptance for publication of a paper in a scientifically recognized, ISI indexed international journal.
December 2011

Laboratory of Atomic Structures and Defects in Advanced Materials