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We present the ZnO (NPs) core-shell nanoparticles synthesised by the hydrolysis method [1-3] and the influence of various synthesis parameters on the morphological and optical properties of thin films containing these ZnO NPs characterized using Raman, SEM and spectroscopic methods. Their performance as white phosphors is then evaluated, through the measurements of their photoluminescent quantum yield. The synthesis of phosphors without rare earths is thus shown, allowing a better understanding of the role of the composition chemistry of the particles in their photoluminescence (PL) properties. Finally, the spectroscopic studies conducted permit to analyze the luminescence mechanisms occurring between core and the shell in NPs and more globally, in the mesospheres in which the NPs are organized within the thin layers. The possibility to apply them in white LEDs is also demonstrated.Another family of ZnO-based materials which can be applied in LEDs are ZnO-Alq3 ((tris(8-hydroxyquinolinato)aluminium) in thin polymer layers. We present the optical properties of ZnO-Alq3 layers in various polymer matrices and propose the mechanisms which may be responsible for the PL emission in these materials.References[1] Y. Zhu, A. Apostoluk, P. Gautier, A. Valette, T. Cornier, J. Bluet, K. Masenelli-Varlot, S. Danièle, B. Masenelli, Sci. Rep. 6, 23557 (1-11) 2016.[2] Y. Zhang, A. Apostoluk, C. Theron, T. Cornier, B. Canut, S. Danièle, B. Masenelli, Sci. Rep. 9, 11959 (2019). [3] Y. Zhang, T. Gard, C. Theron, A. Apostoluk, K. Masenelli-Varlot, B. Canut, S. Daniele, B. Masenelli, Applied Surface Science 540 (1), 148343 (2021).

A great economic progress in white LEDs and photovoltaic (PV) markets is possible thanks to the use of lanthanide-free phosphors that are supposed to convert UV light into visible one, thanks to down-conversion (DS) process. ZnO nanoparticles (NPs) have aroused a growing interest, since due to the size reduction, they possess a variety of intrinsic defects (Zn vacancies and O interstitials). These defects can behave as efficient light-emitters, which provide light emission in the visible range. ZnO NPs naturally absorb the UV light thanks to a wide band gap of about 3.37 eV and it can also emit visible light, from yellow to red, depending on the nature of the crystalline and surface defects involved in the emission process. This is so-called “down-shifting”. However, the stability in time of their high photoluminescent quantum yield (PL QY) and easy to scale–up fabrication process (expected for industrial applications) are still challenging issues. Our collaborators from IRCELyon developed a quick and convenient chemical solution approach to get unique mesospheric self-assembly hybrid ZnO system with intense photoluminescent quantum yield of 40-75 % and stable visible emissions. This chemical process is industry-capable and cost effective. The use of a mixture of commercial polyacrylic acid-based polymers can provide large scale amounts of ZnO NPs in clear water suspensions that can be dried and dispersed again in water and the high PL QY is still preserved. The surface functionalization of ZnO NPs also influences their PL QY and the enhancement of this parameter is observed for some specific procedures applied during the synthesis process. ZnO NPs emitting in the visible spectral range can be applied for LED lightning as phosphors or the down-shifting layer on the top of solar cells in order to increase their efficiency in the UV spectral zone.

Styrylquinolines (StQs) are derivatives of stilbene and can undergo various photochemical reactions [1]. They have two activecentres: ethylene group and an endocyclic nitrogen atom. Styryl dyes [2], and styrilquinoline containing compounds were usedfor various sensitive materials, such as sensitizers or desensitizers. The development of new technologies leads to the discoveryof new applications for styrylquinoline dyes in the fields of electroluminescence [3], photochromism [4], and pharmacy [5]. Thestudy of the photochemical properties of 2-styrylquinoline and its several derivatives showed that substituents in the styrylmoiety increase the quantum efficiency of photoisomerization [6].The aim of the study was to present the influence of various substituents on luminescence and optical properties ofstyrylquinoline copolymers. The thin films of synthesized compounds were prepared using the spin-coating technique(Spin200i, POLOS) at a spin rate of 1500 rpm for 60 s. Immediately after the deposition, the films were cured in an oven at50ºC for 180 minutes in order to eliminate any residual solvent. Optical parameters were obtained from absorbancemeasurements. The luminescent properties of prepared thin layers on glass substrates were registered by the HITACHI f-2500fluorescence spectrophotometer in the range of 360-600 nm (λex. = 340 nm, Xe lamp).References:[1] E.N. Gulakova, D.V. Berdnikova, T.M. Aliyeu, Y.V. Fedorov, I.A. Godovikov, O.A. Fedorova, “Regiospecific C-N photocyclization of 2-styrylquinolines,” J. Org. Chem. 79, 5533–5537 (2014).[2] T. Deligeorgiev, A. Vasilev, S. Kaloyanova, J.J. Vaquero, “Styryl dyes – synthesis and applications during the last 15 years,” Soc. Dyers Col. 126, 55–80 (2010).[3] M. Rams-Baron, M. Dulski, A. Mrozek-Wilczkiewicz, M. Korzec, W. Cieslik, E. Spaczyńska, P. Bartczak, A. Ratuszna, J. Polanski, R. Musiol, “Synthesis of New Styrylquinoline Cellular Dyes, Fluorescent Properties, Cellular Localization and Cytotoxic Behavior,” PLoS ONE 10(6), 1-17 (2015).[4] M.F. Budyka, N.I. Potashova, T.N. Gavrishova, V.M. Li, “Design of fully photonic molecular logic gates based on the supramolecular bis-styrylquinoline dyad,” Nanotechnol. Russ. 7, 280–287 (2012).[5] F. Mao, J. Yan, J. Li, X. Jia, H. Miao, Y. Sun, L. Huang, X. Li, “New multi-target-directed small molecules against Alzheimer’s disease: a combination of resveratrol and clioquinol,” Org. Biomol. Chem. 12, 5936–5944 (2014).[6] M.F. Budyka, N.I. Potashova, T.N. Gavrishova, V.M. Li, “Photoisomerization of 2-styrylquinoline in neutral and protonated forms,” High Energy Chem. 42, 446–453 (2008).