Upconverting core@shell type β-NaYF4:Yb3+–Er3+@SiO2 nanorods have been obtained by a two-step synthesis process, which encompasses hydrothermal and microemulsion routes. The synthesized nanomaterial forms stable aqueous colloids and exhibits a bright dual-center emission (λex = 975 nm), i.e., upconversion luminescence of Er3+ and down-shifting emission of Yb3+, located in the first (I-BW) and the second (II-BW) biological windows of the spectral range, respectively. The intensity ratios of the emission bands of Er3+ and Yb3+ observed in the vis–near-infrared (NIR) range monotonously change with temperature, i.e., the thermalized Er3+ levels (2H11/2 → 4I15/2/4S3/2 → 4I15/2) and the nonthermally coupled Yb3+/Er3+ levels (2F5/2 → 2F7/2/4I9/2 → 4I15/2 or 4F9/2 → 4I15/2). Hence, their thermal evolutions have been correlated with temperature using the Boltzmann type distribution and second-order polynomial fits for temperature-sensing purposes, i.e., Er3+ 525/545 nm (max S r = 1.31% K–1) and Yb3+/Er3+ 1010/810 nm (1.64% K–1) or 1010/660 nm (0.96% K–1). Additionally, a fresh chicken breast was used as a tissue imitation in the performed ex vivo experiment, showing the advantage of the use of NIR Yb3+/Er3+ bands, vs. the typically used Er3+ 525/545 nm band ratio, i.e., better penetration of the luminescence signal through the tissue in the I-BW and II-BW. Such nanomaterials can be utilized as accurate and effective, broad-range vis–NIR optical, contactless sensors of temperature.

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.

A novel, contactless optical sensor of pressure based on the luminescence red-shift and bandwidth (full width at half-maximum, fwhm) of the Ce 3+ -doped fluorapatite-Y 6 Ba 4 (SiO 4 ) 6 F 2 powder has been successfully synthesized via a facile solid-state method. The obtained material exhibits a bright blue emission under UV light excitation. It was characterized using powder X-ray diffraction, scanning electron microscopy and luminescence spectroscopy, including high-pressure measurements of excitation and emission spectra, up to above ∼30 GPa. Compression of the material resulted in a significant red-shift of the allowed 4f → 5d and 5d → 4f transitions of Ce 3+ in the excitation and emission spectra, respectively. The pressure-induced monotonic shift of the emission band, as well as changes in the excitation/emission band widths, have been correlated with pressure for sensing purposes. The material exhibits a high pressure sensitivity (dλ/dP ≈ 0.63 nm/GPa) and outstanding signal intensity at high-pressure conditions (∼90% of the initial intensity at around 20 GPa) with minimal pressure-induced quenching of luminescence. KEYWORDS: Ce 3+ doping, contactless pressure gauge, compression in DAC, lanthanide ions (Ln 3+ ), luminescent functional materials, Y 6 Ba 4 (SiO 4 ) 6 F 2 apatite phosphors

Absorption spectra of inorganic lanthanide fluorides and oxides.

This work sheds the light on the pump power impact on the performance of luminescent thermometers, which is often underestimated by researchers. The up-converting, inorganic nanoluminophore YVO4:Yb3+, Er3+ (nanothermometer) was...