Since ZnO nanoparticles (NPs) possess a variety of intrinsic defects, they can provide a wide spectrum of visible emission, without adding any impurity or any doping atoms. They are attracting more and more interest as a material for light sources and energy downshifting systems. However, defect emission with a high luminescence quantum efficiency (PL QY) is difficult to obtain. Here, we present the co-precipitation synthesis parameters permitting to attain ZnO NPs with highly visible PL QYs. We found that the nature of zinc precursors and alkaline hydroxide (KOH or LiOH) used in this method affects the emission spectra and the PL QY of the as-grown ZnO NPs. LiOH is found to have an advantageous effect on the visible emission efficiency when added during the synthesis of the ZnO NPs. More precisely, LiOH permits to increase the emission efficiency in the visible up to 13%. We discuss the effects of the nanoparticle size, the morphology and the surface stabilization on the enhancement of the luminescent emission efficiency. Various spectral contributions to the luminescent emission were also examined, in order to achieve a control of the defect emission to increase its efficiency.

We present a general and in-depth study of the effect of dopants in hybrid inorganic/organic ZnO/PAA (polyacrylic acid) nanocomposites. These dopants vary as much by their ionic size, as by their electronic valence and some of them have been used in ZnO due to their known magnetic and/or optical properties. The chemical nature of the dopants controls their ability to incorporate into ZnO crystal lattice. Three concentrations (0.1%, 1% and 5%) of dopants were studied in order to compare the effect of the concentration with the results obtained previously in the literature. Our results confirm in the first place the trend observed in the literature, that increase in dopant concentration leads to quenching of visible luminescence for ZnO nanocrystals obtained by very different processes. However, the degradation of photoluminescence quantum yield (PL QY) is not inevitable in our nanocomposites. At low doping concentration for some dopants with a small or comparable ionic radius than Zn²⁺, PL QY can be maintained or even improved, making it possible to tune the visible emission spectrum between 2.17 eV and 2.46 eV. This opens up the prospect of synthesizing phosphors without rare earth for white LEDs, whose spectrum can be tuned to render warm or cold white light, by a chemical synthesis process with a low environmental impact.

For the first time, organic light-emitting diodes (OLEDs) based on bis(8-hydroxyquinoline) zinc with a styryl group (ZnStq) dispersed in poly(N-vinylcarbazole) matrix (ZnStq_R:PVK, where R = H, Cl, OCH₃) were fabricated. The ZnStq_R:PVK films made via the spin-coating method were used as the active layer in these devices. The produced OLEDs showed strong electroluminescence with yellow emissions at 590, 587 and 578 nm for the ZnStq_H:PVK, ZnStq_Cl:PVK and ZnStq_OCH₃:PVK, respectively. For all the studied thin films, the main photoluminescence emission bands were observed between 565 and 571 nm. The OLED with the ZnStq_OCH₃:PVK layer with a narrow electroluminescence spectrum was found to have sufficient color purity to produce ultra-high-resolution displays with reduced power consumption (full width at half maximum of 59 nm, maximum brightness of 2244 cd/m² and maximum current efficiency of 1.24 cd/A, with a turn-on voltage of 6.94 V and a threshold voltage of 7.35 V). To characterize the photophysical properties of the active layer, the ZnStq_R:PVK layers samples were additionally deposited on glass and silicon substrates. We found that the obtained results predestine ZnStq_R:PVK layers for use in the lighting industry in the future.

The paper presents research focused on the efficiency improvement of inorganic flexible thin-film solar cells, using energy converting layers. The light capture enhancement was achieved through the introduction of layers based on rare-earth elements, as top coatings on the amorphous silicon photovoltaic structures. Such luminescent layers are converting high-energy photons into low-energy ones, which are more efficient in photovoltaic conversion of the investigated solar cells. Towards this goal, powders consisting rare-earth elements were applied as active particles in polymer layer. For practical experiments, the screen-printing method, as a cheap, reliable and industrially-ready technology was used for layers deposition. For the experiments two compositions were selected: Sr4Al14O25: Eu,Dy (BGL-300M) and SrAl2O4: Eu,Dy (G-300M). These materials are characterized by excellent thermal and optical stability and interesting luminescent properties (they absorb ultraviolet and emit in the visible range). For the verification of investigated materials and methods, various compositions of powders and proportions were tested and analyzed.