ABOUT US  

Joint scientific objective of our research is definitive and unique characterization of application grade properties of complex oxide based multifunctional materials in terms of the effect of chemical composition, atomic structure, intrinsic dynamics, and temperature. To find this characterization is a challenging task, due the complexity of these materials and the fact that they are on the intersection of physics, chemistry and mathematics where the microscopic and macroscopic methods of description and application of large scale facilities based spectroscopy meet. 

PEOPLES

Head, senior research fellow,  Eriks Klotins Dr.phys 

Contacts :

Eriks Klotins
Phone: +371 67187866
Fax: +371 67132778
E-mail: klotins@cfi.lu.lv

Postal address:

Eriks Klotins 
8 Kengaraga Str.
Institute of Solid State Physics
Riga, LV-1063
Latvia
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 Head of synchrotron radiation spectroscopy group,
senior research fellow Vladimir Pankratov Dr.phys  


PhD students
Liana Shirmane assistant


Former members

Eugene Gabrusenoks Dr.phys (2008)
Ainars Kuznetsov stud.phys. (2008)
Aleksander Bely stud.phys (2008)
Davis Engers stud.phys (2010)
Darja Kasjane assistant (2011)

RESEARCH TOPICS

General research area: theoretical aspects of nanoscale excitations in complex oxides. Relaxation of electronic excitation and energy transfer processes as well as radiation damages in inorganic bulk and nanosized materials.

Preferred topics:
• Extension of ab initio statistics beyond conventional models of spatial invariance.
• Structural instability in perovskites.
• Energy – entropy balance in nonlinear lattices.
• Optical, luminescence and photoemission properties of inorganic bulk and nano materials under synchrotron radiation.

RECENT RESULTS  

Recent results are addressed to prototypical models of complex oxides, especially perovskites, and mathematical techniques reproducing dielectric hysteresis and polarization switching (2005 ), emergence of polar domains and ergodicity breaking ( 2008), energy-entropy balance(2009) , modulation instability(2010) and the nature of polar nanoregions in ferroelectric relaxors (2011).  

The mathematical techniques that have actualized includes symplectic integration of Fokker-Planck equations, Klein-Gordon – discrete nonlinear Schrödinger equation approach and discrete variable representation of problems going beyond translational invariance.

Synchrotron (including VUV) spectroscopy is implemented as the key experimental tool in investigation of optical and luminescence properties of prospective materials with special emphasis on bulk and nano phosphors, scintillators, perovskites, and semiconductor nanocrystals.

INTERNATIONAL COLLABORATION  

Dr. A. Kotlov, HASYLAB at DESY, (Hamburg, Germany)
Prof. H. von Seggern Darmstadt University of Technology (Germany)
Dr. J. Zimmermann, Darmstadt University of Technology (Germany)
Prof. C. Feldmann, Karlsruhe Institute of Technology (Germany)
Prof. B. Bech Nielsen, Aarhus University (Denmark)
Prof. A. Nylandsted Larsen, Aarhus University (Denmark)
Prof. Wieslaw Strek, Wroclaw University (Poland)

MAIN PUBLICATIONS  

Complex oxides 

• E. Klotins, A.I. Popov, V. Pankratov, L. Shirmane, D. Engers, Polar nanoregions in Pb(Mg1/3Nb2/3)O3 (PMN): insights from a supercell approach ,Cent. Eur. J. Phys. • 9(2) • 2011 • 438-445
• E. Klotins, Intrinsic localized excitations in nonlinear lattices: Heuristic explanation for the nature of polar nanoregions?, Physica E 42 (2010) 614-617 
• E. Klotins, A. Kuznetsov, A. Bely, Polarization Response Explored by Joint Hamiltonian and Stochastic Approach, Applied Physics A , (2009) 96: 549-555
• E. Klotins, A. Kuznetsov, Mesoscopic scale structural instability in ferroelectrics, Ferroelectrics ,378: 111120,2009
• E. Klotins, Symplectic integration approach for metastable systems, Eur. Phys. J. B 50, 315 – 320 (2006)
• E. Klotins,Relaxation dynamics of metastable systems: application to polar medium Physica A, 340 (2004) 196-200

Optical, luminescence and photoemission properties

• A.Kalinko, A. Kotlov, A., Kuzmin, V. Pankratov, A.I. , Popov, L., Shirmane, Electronic excitations in ZnWO4 and ZnxNi1-xWO4 (x = 0.1 - 0.9) using VUV synchrotron radiation, 2011 Central European Journal of Physics 9 (2), pp. 432-437 0 
• V. Pankratov, A.I. Popov, A. Kotlov, C.Feldmann , Luminescence of nano- and macrosized LaPO4:Ce,Tb excited by synchrotron radiation, 2011 Optical Materials Article in Press DOI: 10.1016/j.optmat.2010.12.019 
• V. Pankratov, V. Osinniy, A. Kotlov, A. Nylandsted Larsen, B, Bech Nielsen ,Si nanocrystals embedded in SiO2: Optical studies in the vacuum ultraviolet range, 2011 Physical Review B - Condensed Matter and Materials Physics 83 (4), art. no. 045308 0
• V. Pankratov, A.I. Popov, S.A. Chernov, A. Zharkouskaya, C. Feldmann, Mechanism for energy transfer processes between Ce3+ and Tb3+ in LaPO4: Ce, Tb nanocrystals by time-resolved luminescence spectroscopy, 2010 Physica Status Solidi (B) Basic Research 247 (9), pp. 2252-2257 
• V.Pankratov, L. Shirmane, T. Chudoba, P. Gluchowski, D. Hreniak, W. Strek, W. Lojkowski, Peculiarities of luminescent properties of cerium doped YAG transparent nanoceramics, 2010 Radiation Measurements 45 (3-6), pp. 392-394
• V. Pankratov, S. Chernov, L. Grigorjeva, T. Chudoba, W. Lojkowski, Luminescence properties and energy transfer processes nanocrystalline cerium doped YAG, IEEE Transactions of Nuclear Science, 55 (2008) 1509-1513
• L. Grigorjeva, D. Millers, V. Pankratov R.T. Williams, R.I. Eglitis, E.A. Kotomin, G. Borstel, Experimental and Theoretical Studies of Polaron Optical Properties in KNbO3 perovskite, Solid State Comm. 129 (2003) 75-81
• V. Pankratov, L. Grigorjeva, D. Millers, S. Chernov, A.S. Voloshinovskii. Luminescence center excited state absorption in tungstates. Journal of Luminescence 94–95 (2001) 427–432
• E.A. Kotomin, R.I. Eglitis, G. Borstel, L. Grigorjeva, D.K. Millers and V. Pankratov. Theoretical and experimental study of radiation defects in KNbO3 perovskite crystals. Nucl. Instrum. and Methods in Phys. Research, B 166-167 (2000) 239-304
• D. Millers, L. Grigorjeva, V. Pankratov, V.A. Trepakov, S.E. Kapphan. Pulsed electron beam excited transient absorption in SrTiO3. Nuclear Instruments and Methods in Physical Research B 194 (2002) 469-473

ILLUSTRATIVE RESULTS 

ERGODICITY BREAKING AND AROUND  
CRITICAL MODE COUPLED TO THE HEATH BATH AND IMPLICATIONS OF ab initio THERMODYNAMICS  
LOCALIZATION TRANSITION AND EMERGENCE OF POLAR NANOREGIONS IN RELAXOR FERROELECTRICS  
Density Functional Theory Beyond Translational Invariance: Discrete Variable Representation