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Some of the old and unrealizable dreams of biomedicine have become possible thanks to the appearance of novel advanced materials such as luminescent nanothermometers, nanoparticles capable of providing a contactless thermal reading through their light emission properties. Luminescent nanothermometers have already been demonstrated to be capable of in vivo subcutaneous punctual thermal reading but their real application as diagnosis tools still requires demonstrating their actual capacity for the acquisition of in vivo, time-resolved subcutaneous thermal images. The transfer from 1D to 2D subcutaneous thermal sensing is blocked in the last years mainly due to the lack of high sensitivity luminescent nanothermometers operating in the infrared biological windows. This work demonstrates how core/shell engineering, in combination with selective rare earth doping, can be used to develop supersensitive infrared luminescent nanothermometers. Erbium, thulium, and ytterbium core-shell LaF 3 nanoparticles, operating within the biological windows, provide thermal sensitivities as large as 5% °C −1 . This "record" sensitivity has allowed for the final acquisition of subcutaneous thermal videos of a living animal. Subsequent analysis of thermal videos allows for an unequivocal determination of intrinsic properties of subcutaneous tissues, opening the venue to the development of novel thermal imaging-based diagnosis tools.

the measured spectroscopic parameter is usually a pressure-induced line shift, i.e., spectral shift of the emission bands of Cr 3+ (ruby) or Sm 2+ . [14,15,20,22] Whereas, in the case of temperature the commonly measured parameter is the luminescence intensity ratio (LIR), i.e., band ratio of two thermally coupled levels (TCLs; separated by ≈200-2000 cm −1 ) of, e.g., Nd 3+ , Er 3+ , or Tm 3+ , which is directly related to the local temperature of the system (probe), and conforms Boltzmann distribution. [3,[23][24][25] A great number of optically active functional materials is based on the Ln 2+/3+ , because of their unique spectroscopic properties, such as multicolor photoluminescence induced by UV or near-infrared (NIR) (energy up-conversion) irradiation, narrow absorption/emission bands, large spectral shift of the emission bands in relation to the absorption ones, long emission lifetimes, etc. [26][27][28][29][30][31][32][33][34][35] Matrices hosting Ln 3+ ions are usually fluorides, oxides, vanadates, phosphates, and borates. [3,4,11,12,[19][20][21][22][23][24][25][26] This is mainly because of their resistance to photobleaching and high temperature treatment, as well as relatively low phonon energy in contrast to organic compounds. [3][4][5][19][20][21][22][23][24][25][26] Moreover, the Ln 3+ -doped inorganic materials may exhibit up-conversion (UC) phenomena, i.e., anti-Stokes emission of higher-energy photons, generated by the absorption of two or more lowerenergy photons. [32,[36][37][38][39] Thanks to the high absorption cross-section of Yb 3+ in the NIR range, and the presence of a ladder-like structure of Ln 3+ energy levels, the upconverting materials codoped with Yb 3+ / Ln 3+ (Ln 3+ = Ho 3+ , Er 3+ , Tm 3+ ) may work not only as temperature sensors, but also as optical "heaters," as during their irradiation with a high-power NIR lasers they locally heat up. [40][41][42][43][44][45][46][47][48] This is due to the occurrence of various nonradiative processes between the Ln 3+ ions, quenching luminescence of the material and leading to heat generation. [43][44][45][46][47][48] Thanks to the efficient light-to-heat conversion, the optical heating phenomenon can be utilized in photothermal therapies, thermophotovoltaics, formation of new materials under extreme conditions, etc. [43][44][45][46][47][48][49] Currently, temperature of the system can be optically monitored in a relatively broad range, starting from cryogenic up to around ≈10 3 K, whereas pressure could be monitored only in the "high-pressure" range (≈10 2 -10 6 bar). These limitations are associated with the fundamental concept of pressure sensing, i.e., measurements of physical parameters directly Currently the lowest optically determinable pressure values are around 10 2 bar, making the pressure below inaccessible for optical detection. This work shows for the first time how to overcome these limitations, and optically monitor the low pressure values in a vacuum region (from ≈10 −5 to 10 −2 bar), utilizing the light-induced and pressure-g...

Lanthanide-based luminescent nanothermometers play a crucial role in optical temperature determination. However, because of the strong thermal quenching of the luminescence, as well as the deterioration of their sensitivity and resolution with temperature elevation, they can operate in a relatively low-temperature range, usually from cryogenic to ≈800 K. In this work, we show how to overcome these limitations and monitor very high-temperature values, with high sensitivity (≈2.1% K −1 ) and good thermal resolution (≈1.4 K) at around 1000 K. As an optical probe of temperature, we chose upconverting Yb 3+ −Tm 3+ codoped YVO 4 nanoparticles. For ratiometric sensing in the low-temperature range, we used the relative intensities of the Tm 3+ emissions associated with the 3 F 2,3 and 3 H 4 thermally coupled levels, that is, 3 F 2,3 → 3 H 6 / 3 H 4 → 3 H 6 (700/800 nm) band intensity ratio. In order to improve sensitivity and resolution in the high-temperature range, we used the 940/800 nm band intensity ratio of the nonthermally coupled levels of Yb 3+ ( 2 F 5/2 → 2 F 7/2 ) and Tm 3+ ( 3 H 4 → 3 H 6 ). These NIR bands are very intense, even at extreme temperature values, and their intensity ratio changes significantly, allowing accurate temperature sensing with high thermal and spatial resolutions. The results presented in this work may be particularly important for industrial applications, such as metallurgy, catalysis, high-temperature synthesis, materials processing and engineering, and so forth, which require rapid, contactless temperature monitoring at extreme conditions.

The potential use of CdTe quantum dots as luminescence nano-probes for lifetime fluorescence nano-thermometry is demonstrated. The maximum thermal sensitivity achievable is strongly dependent on the quantum dot size. For the smallest sizes (close to 1 nm) the lifetime thermal sensitivity overcomes those of conventional nano-probes used in fluorescence lifetime thermometry.