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Accurate contactless thermometry is required in many rapidly developing modern applications such as biomedicine, micro- and nanoelectronics, and integrated optics. Ratiometric luminescence thermal sensing attracts a lot of attention due to its robustness toward systematic errors. Herein, a phonon-assisted upconversion in LuVO4:Nd3+/Yb3+ nanophosphors was successfully applied for temperature measurements within the 323–873 K range via the luminescence intensity ratio technique. Dual-activating samples were obtained by codoping and mixing single-doped nanopowders. The effect of the type of dispersion system and the Yb3+ doping concentration was studied in terms of thermometric performances. The relative thermal sensitivity reached a value of 2.6% K–1, while the best temperature resolution was 0.2 K. The presented findings show the way to enhance the thermometric characteristics of contactless optical sensors. Post-print / Final draft

The specific luminescence behavior of crystalline oxide particles doped with rare earth ions strongly depends on the initial composition of the host material and synthesis conditions. This issue is especially significant for non-isovalent doping in the crystal lattice. In this case, the formation of the structure is accompanied by the formation of point defects serving as charge compensators. The work is devoted to the synthesis of CaWO4:Nd3+ particles in the salt melt (modified Pechini method) and the study of structural and luminescent properties under varying synthesis conditions. It was found that temperature and duration of heat treatment in the salt melt (KCl) affected the crystal structure, the size of coherent scattering regions, luminescence intensity, and lifetime. An increase of heat treatment temperature led to a reduction of luminescence intensity and lifetime due to the formation of point defects. The optimal synthesis conditions for obtaining the highest luminescence intensity of CaWO4:Nd3+ crystalline particles in salt melt were found to be the following Т1= 600 °C; t1=2 h (the stage of polymer gel thermal treatment), Т2= 800 °C; t2=1 h (the stage of thermal treatment in KCl salt melt). As-synthesized CaWO4:Nd3+ powders contain both coarse and fine fractions. However weak particle agglomeration allowed obtaining a water dispersion with individual nanoparticles (up to 200 nm) after ultrasonic treatment. According to the obtained results, the synthesized material is characterized by high luminescence intensity and high dispersion, and promising as fluorescent thermometers and biological labels. Post-print / Final draft

From 27th of April until 31st of May of 2021, Ioffe-LUT Accelerator established six online workshops and a Demo Day for innovative startup companies from Finland and Russia. The workshops concered various, critical components of business development and many of the participating projects had the opportunity to present for international investors on Demo Day. This collaboration has facilitated cross-border business connections in addition to increasing the attractiveness of new innovations for both clients and investors. Publishers version

Contactless optical thermometry is successfully applied for accurate local temperature sensing in many scientific and technological areas. The majority of optical thermometers utilize a ratiometric approach between thermally coupled levels. Such sensors have an inherent limitation of relative thermal sensitivity linked to the maximal energy gap between these levels, which can make them useless for some important applications. Here, we report simple dual-center YVO4:Eu3+ thermometers that do not have this limitation. Thermal sensing using YVO4:Eu3+ nanoparticles is based on monitoring the luminescence intensity ratio between YVO4 host emission and Eu3+ luminescence lines. By taking advantage of the different temperature behavior of the aforementioned emission bands, contactless sensing was demonstrated within the 123–423 K range. High thermometric performances including subdegree temperature resolution (up to 0.2 K) and relative thermal sensitivity (up to 1.4% K–1) at room temperature reveal the good potential of YVO4:Eu3+ phosphors for thermometry and lay a foundation for the future development of dual-center probes. Post-print / Final draft