Project coordinator: Dr.phys. Laima Trinklere
Total funding: 300 000 EUR
Project implementation period: 2018-2021
LZP FLPP Nr. LZP-2018/1-0361
Summary
Thermoluminescence (TL) and optically stimulated luminescence (OSL) are important and actual methods of basic research of dielectrics, besides they are widely practically used in many areas: personal dosimetry, accident dosimetry, medical radiology and laser therapy, archaeological dating, industrial and food control. Still there is a need for new prospective dosimeter materials with tailored properties. Aim of the given project is development of new prospective materials for dosimetry needs and elucidation of energy storage and recombination luminescence mechanisms in them. The following objects will be studied: powders and transparent ceramics of Al2O3, doped AlN–related materials, LiGaO2 crystals. Novel results will be obtained due to unique combination of modern nanotechnology for sample preparation and luminescence-related characterisation methods applied using the computer-controlled equipment with newly developed software. The research team includes both experienced scientists and PhD and BSc students. Implementation of the project will bring new knowledge in the field of basic research of luminescence mechanisms and material science, contribute to development of new prospective dosimeter materials. The dosimeter devices with increased added value elaborated on their basis will be used in many areas, including safe environment, personal safety, medicine and space exploration.
Main results
Irradiation of wide band materials with ionizing radiation or UV light results in ionization and trapping of the released charge carriers on trapping centers. Supply of additional stimulation energy in the form of heat or light releases charge carriers, which participate in recombination processes with light emission. Such light emission is called thermoluminescence (TL) or optically stimulated luminescence (OSL) depending on type of stimulation energy. Application of TL and OSL methods is important and widely spread in many areas: fundamental research of materials, personal dosimetry, accident dosimetry, medical radiology and laser therapy, archaeological dating, industrial, food control and others. TL and OSL dosimetry of UV radiation is important for detection of harmful UV exposure in conditions of ozone depletion, excessive tanning in solariums, application of germicide lamps, as well as in aeronautics and space exploration.
The main aim of the given project is the development of new prospective materials for dosimetry needs and elucidation of energy storage and recombination luminescence mechanisms in them. In our project the prospective wide band materials are studied for use as luminescence detectors of UV and ionizing radiation using the methods of stimulated luminescence.
Objectives of the Project:
1. Elucidation of the recombination processes and characterisation of dosimeter properties of Al2O3 doped with transition metals and rare earths ions, in the form of powders and transparent ceramics, using the photoluminescence (PL) and TL methods. The previous studies have shown that these materials are characterised with high sensitivity to ionizing radiation and are suitable for high dose rates.
2. Clarification of recombination processes in AlN doped with transition metals and rare earths and characterisation of dosimetric properties using the methods of PL and stimulated luminescence. The pure AlN has a large number of advantages as an ionizing radiation detector; however it exhibits a large fading rate, which could be eliminated by doping.
3. Elucidation of recombination processes in complex oxide crystal LiGaO2 using PL and stimulated luminescence methods. The crystal demonstrates strong TL/OSL signal; however, their mechanisms and potential for practical application is not known yet.
4. Development of modern software for TL experiments control and data processing for the new equipment, which will be acquired by ISSP in 2018 and used for the needs of the project
Al2O3
Al2O3 is a widely studied material with many synthesis methods available to produce the alumina ceramics, powders, coatings and crystals. Outstanding mechanical properties, chemical stability and a wide range of interesting optical properties make the material one of the most popular oxides in both science and industry. One of the most widely used personal dosimeter is a TLD-500 – alumina doped with carbon. This study is aimed to perform evaluation of Al2O3 doped with chromium as a ionizing radiation detector for high-dose applications like radiation sterilization dosimetry, dealing with high doses during irradiations of food products, seeds, medical instruments and agents.
Experimental. 20 Al2O3:Cr samples, both pure and doped with Chromium with different concentrations were synthesized by Sol-gel method. Ceramics were sintered at 1400 °C. A range of experimental techniques was used during this study: X-ray fluorescence analysis (XRF), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), scanning electron microscopy (SEM) photoluminescence (PL), x-ray induced luminescence (XRL), thermostimulated luminescence (TL) and optically stimulated luminescence (OSL) (Freiberg Instruments TL/OSL reader).
Results.
All chromium containing samples exhibit strong Cr3+ ion luminescence in red region of spectrum (R1 and R2 lines located at 691-693nm. The sample with 0.2 wt% Cr2O3 was proven to be the best for the application as was determined by the intensity of TL signal. TL measurements were conducted from 20 °C to 450 °C. To determine the optimal concentration a constant irradiation time of 30 min was used and a 10 min delay time after irradiation to avoid registering sample afterglow. The spectral distribution analysis was performed for all TL peaks and it is evident that the same recombination process as during the x-ray induced luminescence takes place during TL: the main contributors are Cr3+ ions, see Fig.1, a and b. During dopant concentration optimisation, 26 PL, 26 TL, 81 EDX, 152 SEM and 9 XRD measurements were performed to conclude previous statements.
The estimated linearity range for the samples was found to be around 100 Gy to 5 kGy. After thorough investigation, it has been concluded that Cr2O3 doped alumina can be used as linear dosimeter from 3.3 Gy to 1.65 kGy with a compliance to a linear fit of 0.86 R2 and a Chi-Sqr value of 21.38. This means that Cr2O3-doped alumina could be applied as a high dose dosimeter in a wide range of applications due to its inherit chemical and physical traits. Parabolic relation between dose and registered signal intensity implies that saturation is not reached. Currently available equipment does not permit further research at higher doses that are of particular interest to cosmology. Depth of the charge traps is evaluated as 0.23 eV (at 67 °C), 0.37 eV (at 157 °C) and 1.14 eV (at 286 °C). Fading rate was estimated as permissible for ractical application.
Fig.1, a. X-Ray induced luminescence spectrum of Al2O3:Cr 0.2 wt% sample |
Fig.1, b. Thermostimulated luminescence spectrum of Al2O3:Cr 0.2 wt% sample |
OSL measurements were performed as previously planned. We used a wide spectrum blue, red and yellow diodes, analogues to industrial counterparts, centered at 458, 590 and 850 nm alongside a band filter centered at 750 nm. It was concluded that chromium doped alumina ceramic in a powder form is unusable for OSL dosimetric determination due to inadequate light penetration depth. Translucent or transparent ceramic have to be synthesised to alleviate light diffraction and dispersion, which is a tesk for a post-project period.
Most of the obtained results were published in papers [1] and [8], a number of conference reports [12, 14, 17, 21, 23, 25] and a Bachelor Diploma work [26]. Due to already promising preliminary results, ceramic or monocrystalline alpha alumina with chromium might serve as new promising grounds for further research and optimization as a highly accurate, instantaneous medium to high dose dosimetric material unparalleled to currently available alternatives
AlN
AlN is a wide band gap (Eg=6 eV) material, whose spectral properties are determined by presence of uncontrolled impurities and intrinsic defects, the main role played by oxygen-related defects. It was found that this material possesses a number of very attractive dosimeter features retrieved by TL and OSL methods, such as a higher sensitivity to ionizing radiation and especially to UV irradiation compared to other commercial dosimeters, large linear dynamic dose range, negligible influence of the heating rate on the TL response, spectral sensitivity close to that of human skin and others. However, practical application of AlN dosimeter properties is hampered by high fading rate of the stored signal observed at RT, which was ascribed to tunnel processes due to localised transitions. In the present project the idea was proposed: try to diminish fading rate of TL/OSL response by doping it with transient metals and rare earth elements, providing deep trap and/or designing the band gap by adding Ga to host lattice, thus enveloping the shallow traps. An important task is clarification of luminescence processes and recombination mechanisms in doped AlN material.
Experimental For TL/OSL and PL studies we have received from Riga Technical University a number of AlN ceramics series (around 40), produced of nominally pure AlN micropowder (grain size around 10 μm). The AlN ceramic samples differ in production procedure. The samples were produced from undoped AlN powder and also with doping with different additives (Eu2O3, Ga2O3, GaN, Y2O3 ) with varying concentration (0.5 to 5 wt.%). Several experimental set-ups were used: PL emission and excitation spectra were measured by Edinburgh Instruments spectral system as well as the self-made set-up with a deuterium lamp as an excitation source, monochromators in excitation and luminescence channels and a photomultiplier for luminescence signal detection. PL decay kinetics curves under pulsed ArF (193 nm) and KrF (248 nm) laser excitation were measured with a photomultiplier tube (H6780-04) and an oscilloscope Picoscope 2208. TL properties induced by X-ray and UV irradiation were studied using the newly acquired TL/OSL reader from Freiberg Instruments
Results
1. The carried out experimental results provided comprehensive characterization of AlN ceramic samples, produced from the same AlN powder, both pure and doped with Y2O3, Eu2O3 and GaN under UV irradiation and ionizing radiation [9, 20, 27]. Some results are demonstrated here by the Figures 2-5 for pure AlN (P) and AlN-Y2O3 (Y) samples.
Fig.2. PL emission of P sample excited with xenon lamp at 250 nm (1), 280 nm (2) and with ArF laser at 193 nm (3) at RT; and with ArF laser at 193 nm at 80 K (4) |
Fig.3. PL emission of Y sample excited with xenon lamp at 250 nm (1), 280 nm (2) and with laser at 193 nm (3) at RT; and with laser at 193 nm at 80 K (4) |
Fig.4. 3D presentation of TL for P sample after irradiation with 193 nm laser |
Fig.5. 3D presentation of TL for Y sample after irradiation with 193 nm laser |
The main conclusions concern peculiarities of the photoelectric effect, PL and TL processes and luminescence mechanisms in doped AlN samples and may be summarized as follows:
- In pure and doped AlN ceramics a photoelectric effect is observed under irradiation with UV light from the above- and below- bandgap spectral regions, confirming generation of free charge carriers.
- In all samples the photoluminescence and thermoluminescence emission spectra contain the complex UV-Blue band, consisted mainly of 400 and 480 nm subbands, assigned to recombination luminescence with participation of oxygen-related centres, and the Red band peaking at 600 nm, assigned to uncontrolled manganese impurities (Fig. 2-5). In the AlN:Eu2O3 sample an additional band at 525 nm is observed due to Eu2+ radiative transitions.
- In all samples a novel band at 320 nm is found (Fig.2 and 3), which is present in PL under the 193 and 280 nm excitation, and is absent in TL. It is preliminary ascribed to recombination luminescence with participation of (VAl-2ON)0 centres.
- In all samples photoluminescence kinetics shows that emission of all luminescence bands has a complicated behaviour, characterized by superposition of exponents of different duration, varied from nanoseconds to hundreds of minutes. The set of varied time constants is determined by probability of tunnel recombination with partner centres at different separation distance and by recombination with charge carriers isothermally liberated from the traps.
- Decay characteristics of the 400 nm band confirm the concept of the tunnel recombination of the donor-acceptor pair with random distribution of separation distance. Analysis of the 600 nm band’s behaviour allows proposal that in the microsecond time scale luminescence decay is determined by Mn2+ intracenter transitions, while at longer time scales the tunnel recombination processes are determinant. Basing on decay characteristics of Eu2+ emission an assumption is done concerning the 400 nm emission reabsorption by the europium ion under the 248 nm excitation.
- The differences in the PL and TL intensities and relative contribution of the UV-Blue and Red bands observed in the studied samples are explained by influence of sintering procedure and doping impurities on generation of the oxygen-related centres of various types and charging state of intrinsic and impurity defects. 6. No essential effect of the used dopants on the TL glow curve peak (Fig. XX), and hence on the TL signal fading rate, was observed. Doping of AlN ceramics (at least with the particular impurities at the used concentrations) did not change the energy band structure of the material and location of the energy levels of recombination centres and trapping centres, and, hence, did not influence the tunnel recombination process, determining the fading of the irradiation-induced TL signal.
2. Particular experiments were carried out comparing TL properties of AlN-Y2O3 ceramics irradiated with natural Sun light and X-rays [7, 22, 24]. Practical application of AlN ceramics as material for UV light TL dosimetry and in particular, for sunlight dosimetry, has been evaluated. Though AlN could be used for detection of the sunlight dose, its optimal application area lies in the 200-300 nm spectral range. One of application areas could be the antibacterial water treatment, where Hg lamps with characteristic emission line at 254 nm are used. AlN ceramics as a dosimetric material could be used to optimise bactericidal reactor configurations and water flow rate. Another possibility could be space applications, where sunlight spectrum is not influenced by atmospheric absorption and AlN could serve as a good dosimeter for astronaut and equipment extravehicular activities. Taking into account rather high fading rate AlN ceramics could be recommended for quick tests, where it would play an insignificant role.
3. In order to understand better the luminescence process in AlN ceramics and to define the effect of the initial material grain size the comparative study of the luminescence process in AlN nanopowder samples was done [6, 11]. The nanopowder particles have large specific surface area with large concentration of surface defects. Compared to bulk AlN the nanopowders have additional emission bands ascribed to F centres and similar defects. For TL dosimetry use of nanopowders or nanopowder-based ceramics is not desirable.
The main achievement of the present project concerning AlN material is development of the concept of tunnel recombination luminescence for the case of the doped AlN. Though no essential improvement of the dosimetric properties (fading rate, in particular) has been achieved by doping with transition metals and rare earths, the areas for potential application of the material for TL dosimetry of ionizing radiation and UV light were shown. The further improvement of the material for the dosimetry applications could be considered by producing and investigating thick epitaxial layers of AlN with controlled oxygen content, bearing in mind its fundamental role in luminescence processes in AlN.
LiGaO2
LiGaO2 (LGO) is a wide band gap crystal (Eg=5,6-6 eV) with wurtzite base lattice. The present project aims at investigation of luminescence mechanisms in LGO, using the TL and OSL methods in order to estimate its applicability for dosimetry of ionising radiation and UV light. Here novelty is elucidation of complicated recombination process and determination of new area of application for this wide band gap material.
Experimental. LGO samples were obtained from National Sun Yat Sen University, Taiwan. Investigating the complicated recombination luminescence process and electronic structure in LGO we have used not only methods of stimulated luminescence but also a number of other methods, such as PL, luminescence kinetics, photoconductivity, pyroelectric luminescence. Various UV light sources were used as luminescence excitation sources: hydrogen and deuterium gas-discharge sources and excimer lasers using fluorine (157 nm) argon-fluorine (193 nm) and krypton-fluorine (248 nm). X-rays were also used to excite luminescence.
Results
The preliminary studies have unveiled the luminescence spectra composition of the LGO crystal, containing the main bands at 280, 340, 520 and 700 nm all of them caused by recombination of donor-acceptor pairs. In terms of this project a spectral, kinetic and polarization study of the 280 nm band allowed elucidation of its mechanism as recombination process between donor-acceptor pair with random distribution of their separation distance. Results were reported at the FM&NT Conference 2018 [10].
TL properties of LGO were studied after UV, see Fig.8, a. and X-ray irradiation, see Fig. 8, b. LGO is potentially applicable for TL dosimetry needs due to presence of the TL peak at 350 K and TL emission spectrum in visible region. Results of this study were presented at the SSD 19 conference [13].
A special study was undertaken to determine the microscopic origin of LGO luminescence bands. As a result, the gallium – oxygen bond is attributed to the band at 280 nm and the defect containing lithium (a lithium vacancy with an interstitial lithium ion) is connected with the 340 nm band. Donor – acceptor pairs responsible for the 280 nm luminescence band in LiGaO2, contain a self-trapped electron on a gallium ion and a self-trapped hole on an oxygen ion. The nearest pairs form self-trapped excitons. This study is described in a paper [2].The photoelectric properties of LGO crystal were studied and described in publication [3].
For the first time we have observed the effect of the spontaneous intrinsic luminescence in a LiGaO2 crystal due to pyroelectricity upon cooling or heating of the sample in the absence of external excitation. For the first time kinetic and spectral characteristics of pyroelectric luminescence were recorded, which allowed propose the concept of the mechanism of pyroelectric luminescence in LGO, described in publications [4, 18, 19]. Following the studies of pyroelectric luminescence a series of experiments was undertaken attaching a scintillating phosphor to a LGO crystal and other pyroelectrics and subjecting a pair of the bounded crystals to cooling/heating process. Electron emission from a pyroelectric crystal caused luminescence process in a scintillator sample, characterized with high intensity and kinetic and spectral properties typical for the intrinsic luminescence. This experiment, completing study of luminescence processes in LGO, was reported in [5] and at the LU ISSP Conference, 2020 [18].
At present we can assume that the luminescence process in LGO is elucidated due to our studies in terms of the present project. These results are new contribution to basic knowledge of electronic structure and spectral properties of wide band crystals. Besides, the novel understanding of the pyroelectric luminescence was derived basing on kinetic and spectral characteristics of this process, obtained for the first time. Moderate intensity of the TL signal caused by ionising radiation and UV light irradiation hardly makes this material relevant for application in TL dosimetry.
Software
New TSL/OSL device provides the ability to acquire large amount of precise and high quality data, which is hard to proficiently analyse using the existing software, therefore a new solution was needed. A software package was created to increase the overall productivity and to provide additional functionality to the newly installed equipment. It is possible to set a specific value monitored by the software in the dataset. Logical event is triggered when the set value has been found within a dataset and when none of the values are capable of fulfilling the criteria, which allows researchers to perform data analysis during an ongoing measurement. During a logical event, a specific signal is sent through a USB port, which in turn can be interpreted by any equipment. A new opportunity has arisen from the created software and its implementation during TL and OSL measurements like fractal analysis and signal intensity controlled OSL.
Impact
Benefits to society. Materials developed in this project can be used for determination and control of the accumulated radiation not only for specific professional needs (medical institutions or scientific institutions in direct work with radiation sources), but also for energy (fusion, nuclear power plants) and production control. Work safety will increase and operators will be able to act more quickly in the event of a radiation leak, or develop radiation generating equipment more carefully. One of the directions of the project is related to the development of dosimetric materials for ultraviolet light detection. With the UV light dosimeters based on the developed new materials, it will be possible to accurately determine the small doses of UV radiation that a person receives in solariums, or using UV rays to disinfect water or instruments.
Problems to be solved by the project. Due to the fact that ionizing radiation and ultraviolet rays are invisible to the human eye, it is important to create devices that can convert this radiation into a visible form - electrical or optical signal. It is more convenient to accumulate the radiation effect over a longer period of time and obtain a signal from the entire accumulation period at one time. Dosimetric devices are based on suitable materials that are sensitive to ionizing radiation and UV light. The main task of the project is to develop - create and describe - such new materials.
Possible solutions. Several materials sensitive to ionizing radiation and UV light have been developed and studied for dosimetry:
- AlN ceramics with impurities of different metal ions in different concentrations;
- Al2O3 ceramics with chromium impurities;
- LiGaO2 crystals.
Cooperation with research and industrial institutions. During the implementation of the project, co - operation took place with
- RTU - scientific cooperation. Target group - scientists, science staff, students;
- Sun Yat Sen University, Taiwan - scientific cooperation. Target group - scientists, students, the civil society.
- Freiberg Instuments, Germany - technical cooperation in developing the hardware and software we need. Target group - entrepreneurs, scientists, students.
MSc Janis Čipa measures TL response of AlN ceramics using the TL/OSL reader LexsygResearch (Freiberg Instruments)
References/deliverables
Papers
1. Usability of Cr-Doped Alumina in Dosimetry. E. Einbergs, A. Zolotarjovs, I. Bite, K. Laganovska, K. Auzins, K. Smits and L. Trinkler. Ceramics 2 (2019) 525–535; doi:10.3390/ceramics2030040, OPEN ACCESS
2. Comparison of luminescence of LiGaO2, Al2O3-Ga and Al2O3-Li crystals. L.Trinkler, A.Trukhin, Mitch M.C.Chou. Latvian J. Phys.Tech. Sc., 6 (2018,) 4-12; .2478/lpts-2018-0038, OPEN ACCESS
3. Photoconductivity & photoelectron emission of LiGaO2 crystal excited in intrinsic absorption range. A. Trukhin, L. Trinkler, Opt. Mat. 93 (2019) 11–14;
4. Spectral and kinetic characteristics of pyroelectric luminescence in LiGaO2. L. Trinkler, A. Trukhin, J. Cipa, B. Berzina, V. Korsaks, Mitch M.C. Chou, Chu-An Li, Opt. Mat. 94 (2019) 15–20, /https://doi.org/10.1016/j.optmat.2019.05.014
5. A. Trukhin, L. Trinkler, A. Zolotarjovs, Pyroelectric activity of LiGaO2, Li2GeO3, Li2B4O7 and LiNbO3 crystals: Pyroelectric luminescence and excitation of cathodoluminescence in scintillator ScPO4. Opt. Mat. 109 (2020) 110391, https://doi.org/10.1016/j.optmat.2020.110391
6. Berzina B. Trinkler L., Korsaks V., Ruska R. Nitrogen vacancy type defect luminescence of AlN nanopowder, Opt. Mat. 108 (2020) 110069, DOI: doi.org/10.1016/j.optmat.2020.110069.
7. Janis Cipa, Laima Trinkler, Baiba Berzina, Thermoluminescence response of AlN:Y2O3 to the Sun and X-ray irradiation, Latvian J. Phys.Tech. Sc.,2021, N1, 3-14. DOI: 10.2478/lpts-2021-0001. OPEN ACCESS
8. E. Einbergs, A. Zolotarjovs, I. Bite, J. Cipa, V. Vitola, K. Laganovska, L. Trinkler, Re-evaluation of chromium doped alumina for dosimetric applications, Latvian J. Phys.Tech. Sc., 1 (2021) 15-22, DOI: 10.2478/lpts-2021-0002. OPEN ACCESS
9. L.Trinkler, A.Trukhin, J.Cipa, B.Berzina, UV light induced processes in pure and doped AlN ceramics, , Optical Materials 121 (2021) 111550; doi.org/10.1016/j.optmat.2021.111550.
Conferences
10. L.Trinkler et al, 280 nm emission band in LiGaO2. FM&NT-2018, October 2-5, 2018, Riga, Latvia, Book of Abstracts p.79.
11. B.Berzina, et al, F-centres as luminescent defects in AlN and hBN. International Workshop on Nitride semiconductors IWN2018, November 11-16, 2018, Kanazawa, Japan. Tech. digest p.312.
12. E. Einbergs, et al. With chrome doped alumina usability in dosimetry., 35th Scientific Conference of ISSP UL, February 20– 22, 2019, Riga, Latvia, Book of Abstracts, p. 28.
13. L.Trinkler et al. Luminescence properties of LiGaO2 crystal and its potential application in dosimetry, Abstracts of SSD-19 conference, Hiroshima, Japan, Sept 15-20, 2019, p. 372.
14. E. Einbergs, et al, Usability of chrome doped alumina in dosimetry. 21-st International conference-school “Advanced materials and technologies”, 2019, Palanga, Lithuania, Book of abstracts p. 97.
15. J. Cipa, et al,Spectral analysis of pyroelectric effect in LiGaO2, 21-s International conference-school “Advanced materials and technologies”, 2019, Palanga, Lithuania, Book of abstracts p. 84.
16. J. Cipa, Use of TL/OSL reader “Freiberg Instruments” for characterization of new dosimetric materials, 36th Scientific Conference of ISSP UL, 2020, Riga, Latvia, Abstracts, p. 51.
17. E. Einbergs, et al, Chromium doped alumina usability in dosimetry., 36th Scientific Conference of ISSP UL, February 11– 13, 2020, Riga, Latvia, Book of Abstracts, p. 45.
18.A.Trukhin, et al, Energy transfer of pyroelectric crystals to luminophores, 36th Scientific Conference of ISSP UL, February 11– 13, 2020, Riga, Latvia, Book of Abstracts, p. 11.
19. L.Trinkler, et al, Luminescence of LiGaO2 crystal – mechanisms and potential application. Abstracts of FMNT 2020, Vilnius, Lithuania, Nov. 23-26, 2020. p. 20.
20. J. Cipa, et al, Improving dosimetric properties of AlN by doping with rare earth metals. Abstracts of FMNT 2020, Vilnius, Lithuania, Nov. 23-26, 2020, p.142.
21. E. Einbergs, Chromium doped alumina usability in dosimetry, Abstracts of FMNT 2020, Vilnius, Lithuania, Nov. 23-26, 2020, p.153.
22. J.Cipa, et al, Sun and X-ray radiation induced thermoluminescence properties of AlN ceramics, 37th Scientific Conference of ISSP UL, Book of Abstracts, 2021, p. 53
23. E.Einbergs, et al, Chromium doped alumina as a thermoluminescence dosimetry material, 37th Scientific Conference of ISSP UL, Book of Abstracts, 2021, p.54
24. J. Cipa, et al. Thermoluminescence properties of yttria doped AlN ceramics after Sunlight and X-ray irradiation. International conference-school “Advanced materials and technologies”, 2021, Palanga, Lithuania, Book of abstracts A-P111.
25. E.Einbergs, Chromium-doped alumina a potential dosimetric material. International conference-school “Advanced materials and technologies”, 2021, Palanga, Lithuania, Abstracts C-P108.
Defended thesis
26. BSc thesis. Ernests Einbergs. Chromium doped alumina usability in dosimetry, UL, Riga, 2019.
27. MSc thesis. Jānis Čipa. Luminescence properties of doped AlN ceramics. University of Latvia, Riga, 2021.
28. Doctoral thesis. Aleksejs Zolotarjovs. Optical properties of plasma electrolytic oxidation coatings on aluminium alloy surface. Riga, 2021.