Laboratory of Optical Materials

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.

Bohacek, P., Krasnikov, A., Nikl, M., Zazubovich, S., Zolotarjovs, A. On low-temperature luminescence quenching in Gd3(Ga,Al)5O12:Ce crystals (2019) Optical Materials, 95, art. no. 109252, . DOI: 10.1016/j.optmat.2019.109252

Cipa, J., Zarins, A., Supe, A., Kizane, G., Zolotarjovs, A., Baumane, L., Trinkler, L., Leys, O., Knitter, R. X-ray induced defects in advanced lithium orthosilicate pebbles with additions of lithium metatitanate (2019) Fusion Engineering and Design, 143, pp. 10-15. DOI: 10.1016/j.fusengdes.2019.03.096
 

Zolotarjovs, A., Smits, K., Laganovska, K., Bite, I., Grigorjeva, L., Auzins, K., Millers, D., Skuja, L. Thermostimulated luminescence of plasma electrolytic oxidation coatings on 6082 aluminium surface (2019) Radiation Measurements, 124, pp. 29-34. DOI: 10.1016/j.radmeas.2019.02.020

Grigorjeva, L., Grube, J., Bite, I., Zolotarjovs, A., Smits, K., Millers, D., Rodnyi, P., Chernenko, K. Sub-nanosecond excitonic luminescence in ZnO:In nanocrystals (2019) Radiation Measurements, 123, pp. 69-73. DOI: 10.1016/j.radmeas.2019.02.016
 

Korzhik, M., Alenkov, V., Buzanov, O., Fedorov, A., Dosovitskiy, G., Grigorjeva, L., Mechinsky, V., Sokolov, P., Tratsiak, Y., Zolotarjovs, A., Dormenev, V., Dosovitskiy, A., Agrawal, D., Anniyev, T., Vasilyev, M., Khabashesku, V. Nanoengineered Gd 3 Al 2 Ga 3 O 12 Scintillation Materials with Disordered Garnet Structure for Novel Detectors of Ionizing Radiation (2019) Crystal Research and Technology, 54 (4), art. no. 1800172, . DOI: 10.1002/crat.201800172
 

Grigorjeva, L., Zolotarjovs, A., Bite, I., Grube, J., Millers, D. Electronic processes in doped ZnO nanopowders (2019) IOP Conference Series: Materials Science and Engineering, 503 (1), art. no. 012017, . DOI: 10.1088/1757-899X/503/1/012017
 

Vitola, V., Millers, D., Smits, K., Bite, I., Zolotarjovs, A. The search for defects in undoped SrAl2O4 material (2019) Optical Materials, 87, pp. 48-52. DOI: 10.1016/j.optmat.2018.06.004
 

Vitola, V., Millers, D., Bite, I., Smits, K., Spustaka, A. Recent progress in understanding the persistent luminescence in SrAl2O4:Eu,Dy (2019) Materials Science and Technology (United Kingdom), 35 (14), pp. 1661-1677. DOI: 10.1080/02670836.2019.1649802
 

Rucins, M., Dimitrijevs, P., Pajuste, K., Petrichenko, O., Jackevica, L., Gulbe, A., Kibilda, S., Smits, K., Plotniece, M., Tirzite, D., Pajuste, K., Sobolev, A., Liepins, J., Domracheva, I., Plotniece, A. Contribution of molecular structure to self-assembling and biological properties of bifunctional lipid-like 4-(N-alkylpyridinium)-1,4-Dihydropyridines (2019) Pharmaceutics, 11 (3), art. no. 115, .DOI: 10.3390/pharmaceutics11030115
 

Skuja, L., Ollier, N., Kajihara, K., Smits, K. Creation of glass-characteristic point defects in crystalline SiO2 by 2.5 MeV electrons and by fast neutrons (2019) Journal of Non-Crystalline Solids, 505, pp. 252-259. DOI: 10.1016/j.jnoncrysol.2018.11.014
 

Ristić, I., Miletić, A., Vukić, N., Marinović-Cincović, M., Smits, K., Cakić, S., Pilić, B. Characterization of electrospun poly(lactide) composites containing multiwalled carbon nanotubes (2019) Journal of Thermoplastic Composite Materials, . DOI: 10.1177/0892705719857780
 

Trukhin, A.N. Luminescence of natural α-quartz crystal with aluminum, alkali and noble ions impurities (2019) Journal of Luminescence, 214, art. no. 116602, . DOI: 10.1016/j.jlumin.2019.116602

Trukhin, A.N. Luminescence of localized states in oxidized and fluorinated silica glass (2019) Journal of Non-Crystalline Solids, 521, art. no. 119525, . DOI: 10.1016/j.jnoncrysol.2019

Trinkler, L., Trukhin, A., Cipa, J., Berzina, B., Korsaks, V., Chou, M.M.C., Li, C.-A. Spectral and kinetic characteristics of pyroelectric luminescence in LiGaO2 (2019) Optical Materials, 94, pp. 15-20. DOI: 10.1016/j.optmat.2019.05.014
 

Trukhin, A., Trinkler, L. Photoconductivity & photoelectron emission of LiGaO2 crystal excited in intrinsic absorption range (2019) Optical Materials, 93, pp. 11-14. DOI: 10.1016/j.optmat.2019.05.005
 

Trukhin, A.N. Photoelectric response of localized states in silica glass (2019) Journal of Non-Crystalline Solids, 511, pp. 161-165. DOI: 10.1016/j.jnoncrysol.2019.02.002
 

Trukhin, A., Antuzevics, A. Photoluminescence and Electron Spin Resonance of Silicon Dioxide Crystal with Rutile Structure (Stishovite) (2019) Physica Status Solidi (A) Applications and Materials Science, 216 (3), art. no. 1800457, DOI: 10.1002/pssa.201800457

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