Project Summary

Activity Nr 1 - „hBN powder”.

It was planned to study luminescence spectra in wide temperature range (8-300 K) as well as the effect of environment gas on luminescence spectra for hBN commercially available powders and nanopowders.

The planned measurements were fulfilled completely. The following measurements were done for hBN powders with different grain size: luminescence and excitation spectra as well as luminescence kinetics, which allow detecting of luminescence mechanisms and assuming of corresponding luminescence centres. The implemented studies allow conclusion that hBN is a perspective material for production of oxygen gas sensor.

The obtained results are summarised in measurement package and described in a paper submitted for publication in the „ Journal of Optical Materials”.

Activity Nr 2 – „AlN nanopowder”.

It was planned to study the effect of vacuum and different gases on luminescence of AlN nanopowder. The nanopowders with average grain size of 60 nm produced at RTU Institute of Inorganic Chemistry. AlN luminescence and excitation spectra were measured in wide temperature range (8-300 K) in order to determine type of luminescence centres and corresponding mechanisms.

The planned measurements were fulfilled. Studies of luminescence caused by native defects have shown that AlN nanopowder is a perspective material for detection of oxygen in gas mixture. Blue luminescence of the material is sensitive to oxygen surrounding the sample, which causes reduction of luminescence intensity.

The obtained results of measurements are summarised in measurements package and described in a European patent.

Patent title: „AlN NANOPOWDER – MATERIAL FOR OXYGEN GAS OPTICAL SENSORS”. Authors: Baiba Berzina, Valdis Korsaks, Laima Trinkler, and Janis Grabis.

Activity Nr 3 – „Metal oxides”.

It was planned to study the effect of ambient gases on luminescence of ZnO, TiO2 nanocrystals. Materials were synthesised in RTU Institute of Inorganic Chemistry.

Spectral and kinetic characteristics of luminescence of metal oxide nanocrystals (ZnO, TiO2) were studied for samples inserted in air atmosphere and vacuum as well as in gas mixture at room temperature. The obtained results are summarised in the work package.

Activity Nr 4 – „Activated metal oxides”.

It was planned to study the effect of oxygen on luminescence of metal oxide nanocrystals activated with Al and rear earth elements. Luminescence spectra are measured for metal oxides activated with Al and Eu3+ and inserted in vacuum, oxygen and gases mixture in order to determine the effect of activators on material sensitivity to gases.

Metal oxides activated with Al and rear earth elements are produced with 3 methods: sol-gel, plasma electrolytic oxidation, and evaporation-condensation in HELIOTRON reactor. Complex measurements of the produced nanocrystals have been done including spectral and kinetic methods, crystal structure determination with XRD method, composition quantitative analysis with EDAX method, morphology study with electro microscopic methods.

All studied metal oxides actively interact with oxygen, while interaction with nitrogen or argon is not strong. Among all studied metal oxides the most efficient interaction with oxygen is shown by ZnO. Nanocrystals of metal oxides produced in HELIOTRON reactor show good repeatability of results. Interaction of metal oxide nanocrystals with ambient gas depends on nanocrystal size. In the same time nanocrystals of similar size produced by different methods demonstrate different interaction with gases. Morphological studies show that possible reason of this effect is mutual aggregation of nanoparticles.

In the result of the studies it is figured out that luminescence of nanocrystals of activated metal oxides depends on oxygen content in ambient atmosphere. That means that these materials can be used for production of sensitive elements of oxygen sensors. Among the studied materials zinc oxideisthe most prospective for production of sensitive element of oxygen sensor activated, showing the highest sensitivity. The most successive technical solution for production of luminescent oxygen detector is obtained using the coating of activated ZnO nanocrystals on metal zinc oxide. Thus the results of the fulfilled studies are the essential contribution to the solution of mentioned problems.

The results obtained are reflected in measurements package and publication: L.Grigorjeva, et.al Sensors and Actuators. The article is available online: DOI: http://dx.doi.org/doi:10.1016/j.san.2015.09.018

Activity Nr 5 –„ ZnO nanocomposites”

It was planned to study structural and luminescence properties of ZnO nanocomposites.

ZnO nanocomposites were produced integrating ZnO powder (5 weight %) in polypropylene (PP) and polyethylene (PE) matrix or compacting ZnO nanopowder by producing ceramics. Intensification of luminescence of PP/ZnO and PE/ZnO was achieved by irradiation with 150 MeV krypton ions with different dozes. To increase the area of absorbing surface, nanocomposite surface was treated with selective chemical etching and scratching by scanning indenter. Luminescence properties of nanocomposites and their components were studied. Comparative measurements of luminescence intensity of nanocomposites were done in vacuum and air. Stable and repeatable luminescence changes were observed in air. The best results were demonstrated by PP/5% ZnO and ZnO nanopowder compacted into ceramics. The detailed results are given in the result package of the 5th Activity.

The results are published in the paper Physica Scripta 90 094018 (2015) 8 (F.Muktepavela et al.) and summarised in the work package.

Activity Nr 6 – „Oxifluoride glass ceramics”

It was planned to study optical properties of oxyfluoride ceramics in order to create material for UV radiation convertors.

The sample synthesis (improvement of the method), study of repeatability and uniformity and sample luminescence and its dependence on content were studied. Calcium alumosilicate and sodium alumosilicate glass and ceramics samples activated with single or two rear earth activator ions were synthesised. Luminescence spectra were measured and colour parameters determined. Crystal phase of glass ceramics was analysed with XRD method. Magnetic resonance methods were used to study structure of trivalent activator ions in oxyfluoride glass ceramics.

It was found that the best colour and colour indexes are observed in calcium alumosilcate glass ceramics with two activators – europium and dysprosium – produced by sample heating at 7250C temperature.

Oxyfluoride glass ceramic materials produced and studied in terms of the project are prospective for application as white light diode luminophores due to their luminescence properties.

The obtained results are depicted in measurement package and publication: A.Fedotovs, uc., Journal of Non-Crystalline Solids, 429 (2015) 118-121.

Activity Nr 7 - “Publicity”

It is planned to submit 5 original papers in scientific journals or conference proceedings with citation index reaching 50% of citation index in a field of study.

In terms of the project this task is achieved.

List of publications:

1.B. Berzina, V. Korsaks, L. Trinkler, A. Sarakovskis, J. Grube, and S. Bellucci„Blue luminescence of hexagonal boron nitride”, Journal of Optical Materials, submitted 31.08.2015. Nr. OM-D-15-00975. (submitted) 1. Activity Nr.1.

1. L.Grigorjeva, D. Millers, K.Smits, A.Zolotarjovs „Gas sensitive luminescence of ZnO coatings obtained by plazma electrolytic oxidation”, Sensors and Actuators. Raksts ir pieejams internetā „ON LINE” versijā, DOI: http://dx.doi.org/doi:10.1016/j.san.2015.09.018 Activity Nr.4.

2. Faina Muktupavela, Larisa Grigorjeva, Karlis Kundzins, Elena Gorikhova, Piotr Rodnyij, „Structure,nanohardness and photoluminescence of ZnO ceramics based on nanopowders”, Phys. Scr. 90 (2015) 094018.

Activity Nr.5.

3. Anatolijs Sarakovskis, Guna Krieke, „Upconvertion luminescence in erbium doped transparent oxyfluoride glass ceramics containing hexagonal NaYF4 nanocrystals”, Journal of the European Ceramics Society, (2015).

(Accepted): JECS-D-15-00298.Activity Nr.6.

4. A.Fedotovs, A.Antuzevics, U.Rogulis, M.Kemere, R. Ignatans, „ Electron paramagnetic resonance and magnetic circular dichroism of Gd ions in oxyfluoride glass ceramics containing CaF2 nanocrystals”, Journal of Non-Crystalline Solids, 429 (2015) 118-121; Activity Nr.6.

8. Activity Nr 8 - “Patent”

It is planned to submit European patent.

One European patent is submitted basing on the results of the 2nd Activity.

Patent title: „AlN NANOPOWDER – MATERIAL FOR OXYGEN GAS OPTICAL SENSORS”. Authors: Baiba Berzina, Valdis Korsaks, Laima Trinkler, and Janis Grabis.