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Single doped CaWO4:Er3+ phosphors were synthesized and studied for application of optical thermal sensing within a wide range of 98–773 K. Ratiometric strategy utilizing two luminescence intensity ratios, one between host and Er3+ band (LIR1) and second between different Er3+ transitions (LIR2), results in self-referencing temperature readouts. The presence of two temperature-dependent parameters could improve thermometric characteristics and broaden the working temperature range compared to a usual single-parameter thermometer. Thermometric performances of prepared samples were evaluated in terms of thermal sensitivities, temperature resolution and repeatability. The highest sensitivity of 2.09% K−1@300 K was found for LIR1, whereas LIR2 provided more accurate thermal sensing with a temperature resolution of 0.06–0.1 K. Effect of Er3+ doping concentration on sensing properties were studied. The presented findings indicate that CaWO4:Er3+ phosphors are perspective in dual-mode thermal sensing with high sensitivity and sub-degree resolution.

The treatment of monodisperse carbon nanodots (MCNDs) with a combination of aqueous ammonia and hydrogen peroxide is found to result in a prominent enhancement of their fluorescence efficiency. Depending on the hydrogen peroxide concentration, an increase of the MCNDs quantum yield of up to seven-fold has been achieved. Considering the absence of prominent changes in fluorescence lifetime and fluorescence spectra upon the treatment it is suggested that the observed rise of fluorescence efficiency originates from additional formation of new isolated sp2 domains surrounded by defect sites. The structural modification of MCNDs induced by their treatment with combination of aqueous ammonia and hydrogen peroxide is indicated by both transmission electron microscopy images and infrared spectra. The applied method has insignificant effect on the aggregation properties and size distribution of the studied MCNDs. Taking into account the proposed mechanism, the applied treatment procedure can serve as a basis for a facile approach for modification of emissive properties of various nanocarbon structures.

Achieving a combination of real-time diagnosis and therapy in a single platform with sensitive thermometry and efficient heat production is a crucial step towards controllable photothermal therapy. Here, Nd3+-doped Y2O3 nanoparticles prepared using the combined Pechini-foaming technique operating in the first and second biological windows were demonstrated as thermal sensors within the wide temperature range of 123-873 K, and as heaters with a temperature increase of 100 K. Thermal sensing was performed based on various approaches: luminescence intensity ratio (electronic levels; Stark sublevels), spectral line position and line bandwidth were used as temperature-dependent parameters. The applicability of these sensing parameters, along with relative thermal sensitivity and temperature resolution, are discussed and compared. The influence of Nd3+-doping concentration on thermometer and heater efficiency was also investigated.

Nanocrystalline Eu3+-doped Mg2SiO4 powders were prepared with combined Pechini-solid phase synthesis. The structural properties were investigated with XRD, SEM and Raman spectroscopy. XRD pattern indicated that Mg2SiO4:Eu3+ were obtained with formation of other phase: MgO. Raman spectrum revealed good homogeneity and crystallinity of synthesized nanopowders. The luminescence properties were studied with measurement of excitation and emission spectra and decay curves. The effect of Eu3+ concentration on 5D0 level lifetime was studied. Most probably, the observed shortening of 5D0 level lifetime with Eu3+ concentration is caused by increase of nonradiative process probability.

Lanthanide-doped nanoparticles characterized by their large Stokes' shifts, narrow emission bands, long lifetimes and high photostability are promising candidates for luminescent labels in biological research. That is why investigation of lanthanide-doped nanoparticles' fluorescence in complex biological media (like blood and Intralipid) is of great importance from the standpoint of applicability in medicine and biology. Nanopowder of yttrium aluminum garnet doped with Eu3+ was synthesized by the Pechini method. X-ray diffraction data demonstrated formation of cubic crystalline phase without any impurities. The synthesized sample was found to be well-defined 20–50 nm nanoparticles agglomerated to clusters no bigger than 200 nm in diameter. The emission spectrum of nanocrystalline powder consists of characteristic narrow lines attributed to 5D0–7FJ transitions. It was found that the long lifetime of 5D0 level (4.13 ms) allows using time-resolved techniques to eliminate fluorescence of the biological background. The possibility of the luminescence signal detection of Y3Al5O12:Eu3+ nanopowder (0.14 mg per 1 ml) against the background of blood auto-luminescence was demonstrated. Y3Al5O12:Eu3+ phosphors luminescence in blood media showed timing stability whereas fluorescein luminescence dropped down by a factor of 3 after 20 min. It was found that the luminescence signal of Y3Al5O12:Eu3+ phosphors could be detected through 5 mm of biological tissue. The possibility of independent registration of nanopowders doped with different REI-ions (Eu3+ and Nd3+) was investigated.