Phosphorescent coatings prepared by plasma electrolytic oxidation (2017 - 2019)
Agreement No 18.104.22.168/16/A/182
Duration: 27.02.2017 -31.10.2019
Scientific manager: Dr.phys. Krisjanis Smits
The proposed project foresees studies of luminescent coatings prepared by plasma electrolytic oxidation (PEO). Up to now, PEO coatings were mostly studied because of their tribological properties; however, PEO coatings also have good wear resistance, high hardness and are chemically stable therefore this technology can be applied to form protective coatings on metals. It is known that many oxide based materials exhibit good luminescent properties, however the luminescence of PEO produced oxide layers was not studied before. The first research in this direction was made by private company Elgoo tech in cooperation with Insitute of Solid State Physics University of Latvia.
During planed research project, PEO process will be used to produce luminous aluminium coatings. The analysis of accessible data indicates that PEO synthesis is a promising approach for production of materials with long lasting luminescence, for example SrAl2O4:Eu:Dy. The coatings prepared by PEO will be transparent in blue and UV range, therefore the final long lasting luminescence efficiency is expected to be several times higher than that of luminescent paints currently in use. In addition, coatings could serve as protection for metals since the durability of such coatings is expected to be better compared to paints.
Project updates (30.10.2018)
A publication in Materials & Design presenting a novel method of phosphorescent strontium aluminate coating preparation on aluminum
We are proud to announce that a new publication “Novel method of phosphorescent strontium aluminate coating preparation on aluminum” has been written and published in Materials & Design in October. This publication was funded by the ERDF project “Phosphorescent coatings prepared by plasma electrolytic oxidation” No: Nr.22.214.171.124/16/A/182.
Author list: Ivita Bite, Guna Krieke, Aleksejs Zolotarjovs, Katrina Laganovska, Virginija Liepina, Krisjanis Smits, Krisjanis Auzins,Larisa Grigorjeva, Donats Millers and Linards Skuja
This study presents a novel approach to produce phosphorescent coatings on metal surfaces. Strontium aluminates are the most popular modern phosphorescent materials exhibiting long afterglow at room temperature and a broad spectral distribution of luminescence in the visible range. However, despite a large amount of research done, methods for synthesis of such materials remain relatively energy inefficient and environmentally unfriendly. A long-afterglow luminescent coating containing SrAl2O4:Eu2+, Dy3+ is prepared by the plasma electrolytic oxidation on the surface of commercial aluminum alloy Al6082. During the electrical discharges in this process, the strontium aluminate is formed in a similar way to the solid-state reaction method. X-ray powder diffraction analysis confirms that the monoclinic SrAl2O4 phase is present in the coating. Optical properties of the obtained coating were analyzed with luminescence methods classically used for studies of luminophores. The performance of the coating was compared with commercially available strontium aluminate powder. The proposed method of coating synthesis may be of value for the development of energy-efficient and long-lasting automotive and public safety infrastructure.
Keywords: phosphorescent coating, strontium aluminate, long afterglow, persistent luminophore, electrolytic oxidation
Published in Materials & Design
Project updates (22.08.2018)
A new publication in the frame of ERDF Project Nr.126.96.36.199/16/A/182 on fundamental processes in phosphorescent materials has been published "The search for defects in undoped SrAl2O4 material"
Virginija Vitola, Donats Millers, Krisjanis Smits, Ivita Bite, Aleksejs Zolotarjovs
SrAl2O4:Eu,Dy is a very eﬃcient long afterglow phosphor with wide range of possible applications. The luminescence properties and the possible luminescence mechanism of this material have been studied extensively, but there is almost no information available about the undoped material. Therefore, this article deals with the luminescence and thermally stimulated luminescence of an undoped SrAl2O4, revealing the possible defects that might be involved in the creation of the long afterglow in doped material. We conclude that undoped material exhibits some luminescence under X-ray irradiation in low temperature; close to room temperatures luminescence is almost fully thermally quenched in comparison to low temperatures. We can observe F and F2 center luminescence as wellas trace metal luminescence inthe emission spectrum.TSL glow curveyields the peaksthat are close to those observed in material with Eu and Dy doping; therefore these peaks are clearly related to intrinsic defects. The peak at around 400K, that is shifting with rare earth doping, might be due to dopant interaction with intrinsic defects.
Published in Optical Materials
Project updates (28.05.2018)
A significant improvement on the control of various electrical parameters was achieved in the last couple of months due to the planned upgrades of the power supply unit. New limits of coating preparation can be achieved now with higher voltages (up to 1000V) as well as with vastly improved software and automated control algorithms allowing uninterrupted change of any desired parameter in time. This modification allows the in-depth studies of effects of high voltage on coating formation process and implementation of RE ions in it. In addition, the stability of the power supply was improved allowing extra-long processing time on high loads. This is important for the different oxide phase formation as recrystallisation occurs only at longer processing times.
With the new setup a new set of samples was prepared and further optimization of parameters is undergoing. The main aim is to improve PEO coating to match and exceed the performance of similar materials in other forms.
Project updates (31.01.2018)
A new publication on fundamental processes in phosphorescent materials has been published.
V. Liepina, D. Millers * , K. Smits, A. Zolotarjovs, I. Bite
SrAl2O4:Eu,Dy is a very efficient long afterglow phosphor with wide range of possible applications. In this study we carried out the study of X-ray excited luminescence of SrAl2O4:Dy and SrAl2O4:Eu,Dy samples, including the measurements of afterglow at low temperatures within extended time scale. We observed both Eu and Dy luminescence peaks in the afterglow and TSL measurements. In recent articles the tunneling of electron from trap levels to excited Eu luminescence center was discussed, and in this research we conclude that under X-ray irradiation Eu2+ and Dy3+ serve as hole traps; electron tunneling is present in both SrAl2O4:Eu, Dy and SrAl2O4: Dy, and luminescence afterglow at 10 K arises from decay of excited Eu2+ and Dy3+ centers created via electron tunneling from host trap to Eu3+ and Dy4+ ions.
Journal of Physics and Chemistry of Solids
Project updates (31.10.2017)
A certain project milestone has been recently achieved and luminescent coatings with sufficient luminescence intensity to be seen by the naked eye have been acquired. We will continue our work on intensity and luminescence afterglow parameter improvement and it certainly looks like we’re moving in the right direction although of course there’s tons of work still ahead of us.
A publication studying optical properties of strontium aluminate has been submitted and is being reviewed.
We’re also happy to announce that starting September Boriss Poļakovs and Krišjānis Auziņš have joined the project and are actively working to contribute to project’s successful ongoing.
Improvements on PEO reactor chamber (see photo) have been made to insure better repeatability and constant results, allowing to study the coatings with greater detail and less errors. Technical improvements have also been made to aluminum samples – it is now possible to split the samples into smaller pieces with absolutely no potential damage to the coating.