The Optical Materials laboratory specializes in luminescence and other optical phenomena research in various materials, as well as other material characterization methods including (but not limited to) microscopy (SEM, TEM), X-ray diffraction, electron-dispersive x-ray analysis and others.

Scientific degree Name Surname Position Phone number E-mail
Dr.phys. Krisjanis Smits Head of laboratory 67187478 Krisjanis.Smits@cfi.lu.lv
Dr.habil.phys. Donats Millers Senior researcher 28702551 Donats.Millers@cfi.lu.lv
Profesor, Dr.habil.phys. Andrejs Silins Senior researcher 67211405 Andrejs.Silins@cfi.lu.lv
Dr.habil.phys. Linards Skuja Senior researcher 67260756 Linards.Skuja@cfi.lu.lv
Dr.habil.phys. Anatolijs Truhins Senior researcher 67260756 Anatolijs.Truhins@cfi.lu.lv
MSc. Ivita Bite Researcher   Ivita.Bite@cfi.lu.lv
MSc. Katrina Laganovska Researcher   Katrina.Laganovska@cfi.lu.lv
MSc. Aleksejs Zolotarjovs Researcher   Aleksejs.Zolotarjovs@cfi.lu.lv
MSc. Virginija Vitola Research assistant   Virginija.Vitola@lu.lv
BSc. Krisjanis Auzins Engineer   Krisjanis.Auzins@cfi.lu.lv
  Ernests Einbergs Engineer   Ernests.Einbergs@cfi.lu.lv
  Juliana Kepente Engineer   Juliana.Kepente@cfi.lu.lv
  Madara Leimane Engineer   Madara.Leimane@cfi.lu.lv
  Mareks Seņko Engineer   Mareks.Senko@cfi.lu.lv
  Agnese Spustaka Engineer   Agnese.Spustaka@cfi.lu.lv
  Edgars Straumanis Engineer   Edgars.Straumanis@cfi.lu.lv
  Karīna Taranda Engineer   Karina.Taranda@cfi.lu.lv

Various oxides (ZrO2, HfO2, ZnO, SrAl2O4 etc.) doped with rare earth (RE) ions are studied. Optical properties are of main interest; however, laboratory staff is trained to perform other tasks: electron microscopy (SEM, TEM), sample preparation (Plasma Electrolytic Oxidation (PEO), various synthesis methods in a well-equipped chemical lab), as well as other material characterization (EDX, XRF, XRD).

Luminescence properties of ZnO in its various forms (monocrystals, nanopowders, ceramics and coatings) are studied. PEO coating research as well as dopant implementation development with the aim to improve and functionalize optical properties of coating. New PEO structures are produced with their characteristic properties, technologies for practical application of such coatings are developed.

Up-conversion luminescence studies are performed on RE doped ZrO2 and various ceramics.

Thermostimulated luminescence (TSL) methods are developed and applied. Unique developed setup allows the measurement of spectral distribution dependence on temperature. Various heating regimes allow defining the thermal activation energies of traps.

One of the general research fields of the laboratory is also studies of the influence of the amorphous state on the optical, electrical and chemical properties of solid materials.

The main research objects are: (1) silicon dioxide (SiO2) in its multiple crystalline, glassy and amorphous forms, (2) Various amorphous oxide materials related to SiO2, such as germanosilicate glasses and multicomponent silicate glasses. These materials are studied in bulk (monocrystals, polycrystals, glasses) , thin film, fiber and nanoparticle forms.

Silicon dioxide is selected as one of the main research object due to two aspects:

1) Fundamental aspect. Silicon dioxide is one of the few existing simple compounds, which exists both in crystalline and glassy states. This property allows to elucidate the effects of amorphous disorder on optical, electric and other properties of the material.

2) Application-related aspect. Silicon dioxide has a number of outstanding properties, which make it one of the presently most widely used materials in optics, photonics and microelectronics. It is the material of choice for low-loss optical communication fibers and for a plethora of specialty-fibers, for example, fibers for high power laser transmission in medicine or material processing, UV-transmitting fibers for analytical optical instrumentation, radiation-tough fibers for nuclear and space environments, fiber Bragg gratings for information processing and sensors, photonic fibers. High purity SiO2 glass is used in the vast majority of UV bulk optical elements (lenses, prisms, windows). SiO2 films on silicon serve as passivating, masking and dielectric layers in the Si-based microelectronics. Crystalline SiO2 in α-quartz form is used as a resonator in virtually any electronic timekeeping device.

Additional directions of research related to SiO2 in the laboratory are the following:

  1. The studies of optically active point defects in crystalline and glassy SiO2. Silicon dioxide is distinguished by an excellent optical transmissivity in the spectral range from the near infrared (1300nm) up to vacuum UV region (that is why it is No 1 in optical fibers). However, its optical properties are degraded by “point defects” – local deviations from the ideal interconnectivity between Si and O atoms in SiO2 network. Understanding of their structure, optical properties and formation processes is essential for many applications.
  2. Spectroscopic studies of SiO2 crystalline polymorphs. At the room temperature and at normal pressure SiO2 can exist in various polymorphic forms: stable form - α-quartz and metastable forms (α-tridymite, α-cristobalite, coesite, stishovite). It is usually assumed that the closest crystalline counterpart of glassy SiO2 is α-quartz. However, it is considered that in small local regions of amorphous SiO2, in particular, around point defects, there may exist structures, bearing resemblance to other crystalline polymorphs of SiO2.
  3. Studies of doped SiO2 and multicomponent SiO2-related glasses. SiO2 is often doped to obtain the necessary properties, for example, by Ge to increase the refraction coefficient in fiber waveguides and to create fiber optic Bragg gratings, by fluorine to decrease the refraction index or to increase the vacuum-UV transmission, or by rare earth ions to create fiber lasers.
  4. tudies of interstitial molecules in SiO2. Amorphous SiO2 and some crystalline forms of SiO2 (zeolites) have nanosized interstitial spaces in their structure, which can accommodate small molecules. They can be introduced by diffusion (e.g., H2) or created internally by photochemical reactions (O2), or introduced during synthesis (Cl2). Their presence significantly affects the optical properties of SiO2 and their studies are of direct practical interest.
  5. Studies of SiO2 nanoparticles and photochemical properties on surfaces of SiO2. Different SiO2 related nanoparticles and core-shell structures are widely studied for biological applications, e.g., drug transport, photodynamic therapy, sensors. Compared to the crystalline polymorphs, amorphous SiO2 is characterized by large interstitial spaces, which can be considered as internal surfaces. Defects on these internal surfaces bear many similarities to defects on outer surfaces of SiO2, which affect the photo- chemical processes in applications involving SiO2 nanoparticles.

The studies in the laboratory are performed mainly by spectroscopic methods. The available equipment allows using optical absorption and luminescence spectroscopy, time-resolved and luminescence kinetics spectroscopy, infrared absorption, Raman scattering (at several wavelengths) and vacuum-ultraviolet spectroscopy. Low temperature (down to 14K) measurements are available. In cooperation with other laboratories and partners many other investigation methods (e.g., XRD, XRF, EPR...) are available.

Active projects

ERDF project:

Phosphorescent coatings prepared by plasma electrolytic oxidation (2017-2019)

New nanosized upconversion oxide materials (2017 - 2020)

ERANET:

ZnONanoLum (2018-2021)

Latvian Council of Science grants:

Research of luminescence mechanisms and dosimeter properties in prospective nitrides and oxides using TL and OSL methods (2018 - 2021)

Optical properties of advanced silicon dioxide-based materials for ultraviolet and high-power photonics (2018 - 2021)

  

Accomplished projects

ERDF:

Mini spectrometer for food analyses (2018)

ISSP UL Scientific Research Projects for Students and Young Researchers:

PhD.Phys. student Aleksejs Zolotarjovs (2017-2018)

PhD.Chem. student  Ivita Bite (2017-2018)

PhD.Phys. student Aleksejs Zolotarjovs (2016-2017)

MSc.Eng student Katrina Laganovska (2016-2017)

National Research program:

Multufunctional Materials and composites photonic and nanotechnology (IMIS2) (2014 - 2017)

LCS grants:

Spectroscopic studies of advanced dielectrics and wide-gap semiconductors with different local disorders (2013 - 2016)

ERANET:

Metrology at the Nanoscale with Diamonds

ERANET RUS PLUS, NanoRadDos (2016 - 2017)

 

It was found that adding niobium drastically increases activator luminescence intensity in ZrOmatrix, which makes Ln3+ doped zirconia even more attractive for various practical applications. Although this study was based on the luminescence of the Er ion, the phase stabilization, charge compensation, and luminescence properties are expected to be similar for other lanthanide elements. Results suggest that the luminescence intensity of other oxide matrices where lanthanides incorporate in place of tetravalent cations could be increased by addition of Nb ions.

Luminescence properties of ZnO are carried out as the material is applicable in various fields – as fast scintillators, for new generation of luminescence-based light sources, conductive and transparent thin coatings, new generation of laser materials etc. Luminescence and fast induced absorption studies of ZnO monocrystals, nanocrystals as well as ceramics provided new information and understanding of processes inside the material.

Advancements in various PEO directions were achieved:

  1. For the first time, luminescence from PEO coating was observed (Eu3+ in Al2O3 matrix)
  2. A new doping technology was developed for PEO coatings (three-stage pore filling)
  3. PEO coating for dosimetry applications
  4. PEO coating containing SrAl2O4:Eu2+, Dy3+  and showing a long lasting luminescence has been acquired

During the past decade a number of results of fundamental and applied importance for SiO2-based optical materials have been obtained in the Amorphous materials spectroscopy laboratory:

The exact optical properties of technologically important interstitial chlorine molecules in synthetic SiO2 glass were determined and the photochemical formation of interstitial Cl2O molecules by reaction of interstitial Cl2 with photolytic interstitial O atom was detected for the first time.

The influence of the amorphous state of SiO2 on point defect formation has been studied, and it was shown that vacancy-interstitial (Frenkel) mechanism is more efficient than bond dissociation (“dangling bond”) mechanism, while both mechanisms are enhanced by the glassy disorder.

The diffusion of interstitial O2 molecules and interstitial O atoms in the glass network of SiO2 was studied by 18O isotope enrichment, and it was found that the thermal diffusion of O proceeds with network exchange in the form of peroxy linkages (Si-O-O-Si bonds), while excited-state O atom can diffuse as interstitial without exchanging with network oxygens.

Optical absorption spectrum of oxygen dangling bonds (“NBOHC’s”) in irradiated glassy SiO2 in deep-UV and vacuum UV region has been established. This defect is of particular practical importance since it is an efficient absorber and it is present in any irradiated SiO2 glass. However, until our work the exact deep-UV-VUV spectrum was not known due to interference from other overlapping optical bands.

Luminescence of phosphorus-related defects in SiO2 glass and crystals has been investigated, a new ultraviolet emission band (4.6eV) with associated 7.1 eV excitation band was found and related to tetrahedrally coordinated phosphorus atom (P2+ -center or PO43− complex ion) in SiO2 network.

Luminescence of intrinsic oxygen-deficiency related defects and excitons in different SiO2 polymorphs have been studied and reviewed.

These studies are well-known among the international community working in this field, and the laboratory researchers have co-authored several review articles on these topics.

Absorption spectroscopy

FTIR spectroscopy: EQUINOX 55 (10000-400 cm-1 and 22000-7000 cm‑1spectral region) with diffuse reflection cell;

LABOMED UVVIS spectrometer;

Electron beam induced short-lived absorption.

Luminescence spectroscopy

Different excitation sources are available: pulsed electron beam accelerator (10 ns, 270 keV, 1012 el/pulse), X-rays, YAG:Nd laser (266 nm, 532 nm), nitrogen laser (337 nm), conventional Deuterium and Xenon lamps.

Automatic systems are used for luminescence detection – diffraction monochromator with photomultiplier on exit slit or spectrometer with CCD camera. Time-resolved luminescence is detected using photon counting module and multichannel memory module with minimal time bin 250 ps. Also, luminescence and absorption detection using a fast digital storage oscilloscope is possible.

The equipments for luminescence excitation spectra measurements with two momochromators (Horiba iHR320 and Jobin Yvon TRIAX320)

The equipment for TSL studies with different temperature control modes and software for activation energies calculation.

Praparation by plazma electrolytical oxidation (PEO) method. The development of synthesis Al2O3, ZnO, TiO2, ZrO2 undoped and doped with RE ions.

Laboratory instrumentation and equipment:

  • Vacuum ultraviolet monochromators for optical spectroscopy in the spectral range 120nm<λ<250nm: models McPherson 234/302, VM2.
  • Sources of vacuum ultraviolet light: deuterium lamps with MgF2 crystal windows, range 120nm<λ<350nm: Heraeus PSD 200/D200-VUV and Hamamatsu L10366.
  • Excimer laser PSX-100 (λ=157nm, pulse length 5ns.
  • CCD spectrographs for UV, visible and near IR (NIR) spectral ranges (190nm<λ<1150nm): Andor Newton DU971/Shamrock303 and Hamamatsu 10082CAH.
  • Monochromators for UV –visible- infrared ranges (190nm<λ<2000nm): MDR-2, AMKO-LTI and appropriate photomultiplier and photodiode detectors.
  • Multichannel photon counter for kinetic measurements in 100 nanosecond and longer time intervals: Fastcomtec 7882.
  • Cryostats and He refrigerator system for optical measurements in the temperature range 10K to 300K: Heraeus RW2/RGD210/ROK 10-300.
  • Optical and optomechanical elements for flexibly reconfigurable optical experiments involving luminescence and Raman scattering techniques: holders, positioners, filters, polarizers, light sources detectors, data acquisition systems with custom- developed (Labview) software.
  • Custom-built high-sensitivity Raman spectrometer : 532nm 1W excitation, backscattering geometry, registration by cooled CCD..
  • X-ray source for sample irradiation and X-ray induced luminescence measurements: URS60 (50kV, 15mA)
  • Equipment for measuring of UV-to-NIR range spectral losses in multimode optical fiber waveguides and for studying of losses induced by UV light ("solarization") or by ionizing radiation: optical positioners, fiber-optic SMA905 standard patch cables, excimer lasers, light source Ocean Optics DH200.

Bite, I., Krieke, G., Zolotarjovs, A., Laganovska, K., Liepina, V., Smits, K., Auzins, K., Grigorjeva, L., Millers, D., Skuja, L. Novel method of phosphorescent strontium aluminate coating preparation on aluminum (2018) Materials and Design, 160, pp. 794-802. DOI: 10.1016/j.matdes.2018.10.021

Joost, U., Šutka, A., Oja, M., Smits, K., Döbelin, N., Loot, A., Järvekülg, M., Hirsimäki, M., Valden, M., Nõmmiste, E. Reversible Photodoping of TiO2 Nanoparticles for Photochromic Applications (2018) Chemistry of Materials, 30 (24), pp. 8968-8974.  DOI: 10.1021/acs.chemmater.8b04813

Labrador-Páez, L., Jovanović, D.J., Marqués, M.I., Smits, K., Dolić, S.D., Jaque, F., Stanley, H.E., Dramićanin, M.D., García-Solé, J., Haro-González, P., Jaque, D. Unveiling Molecular Changes in Water by Small Luminescent Nanoparticles (2017) Small, 13 (30), art. no. 1700968, .  DOI: 10.1002/smll.201700968

Skuja, L., Kajihara, K., Smits, K., Silins, A., Hosono, H. Luminescence and Raman Detection of Molecular Cl2 and ClClO Molecules in Amorphous SiO2 Matrix (2017) Journal of Physical Chemistry C, 121 (9), pp. 5261-5266.  DOI: 10.1021/acs.jpcc.6b13095

Polyakov, B., Kuzmin, A., Smits, K., Zideluns, J., Butanovs, E., Butikova, J., Vlassov, S., Piskunov, S., Zhukovskii, Y.F. Unexpected epitaxial growth of a few WS2 Layers on {1100} facets of ZnO nanowires (2016) Journal of Physical Chemistry C, 120 (38), pp. 21451-21459.  DOI: 10.1021/acs.jpcc.6b06139

Kajihara, K., Skuja, L., Hosono, H. Diffusion and reactions of photoinduced interstitial oxygen atoms in amorphous SiO2 impregnated with 18O-labeled interstitial oxygen molecules (2014) Journal of Physical Chemistry C, 118 (8), pp. 4282-4286.  DOI: 10.1021/jp412606a

Šutka, A., Käämbre, T., Joost, U., Kooser, K., Kook, M., Duarte, R.F., Kisand, V., Maiorov, M., Döbelin, N., Smits, K. Solvothermal synthesis derived Co-Ga codoped ZnO diluted magnetic degenerated semiconductor nanocrystals (2018) Journal of Alloys and Compounds, 763, pp. 164-172.  DOI: 10.1016/j.jallcom.2018.05.036

Šutka, A., Vanags, M., Joost, U., Šmits, K., Ruža, J., Ločs, J., Kleperis, J., Juhna, T. Aqueous synthesis of Z-scheme photocatalyst powders and thin-film photoanodes from earth abundant elements (2018) Journal of Environmental Chemical Engineering, 6 (2), pp. 2606-2615.  DOI: 10.1016/j.jece.2018.04.003

Šutka, A., Döbelin, N., Joost, U., Smits, K., Kisand, V., Maiorov, M., Kooser, K., Kook, M., Duarte, R.F., Käämbre, T. Facile synthesis of magnetically separable CoFe2O4/Ag2O/Ag2CO3 nanoheterostructures with high photocatalytic performance under visible light and enhanced stability against photodegradation (2017) Journal of Environmental Chemical Engineering, 5 (4), pp. 3455-3462.  DOI: 10.1016/j.jece.2017.07.009

Grigorjeva, L., Millers, D., Smits, K., Zolotarjovs, A. Gas sensitive luminescence of ZnO coatings obtained by plazma electrolytic oxidation (2015) Sensors and Actuators, A: Physical, 234, pp. 290-293.  DOI: 10.1016/j.sna.2015.09.018