of luminescence signal in comparison to other methods, relatively fast response, and a good spatial resolution. Temperature can be determined from different features of luminescence, such as excitation and emission band positions and bandwidths, emission band intensities, luminescence intensity ratio (LIR; the ratio of intensities of two emission bands), anisotropy, emission decay-or rise-times, etc. [2] Temperature readouts from LIR and emission lifetime are by far the most exploited luminescence thermometry methods. Both readouts are self-referencing and are not affected by fluctuations in the excitation and signal detection. Luminescence of any substance is strongly affected by temperature, and, thus, variety of materials may be utilized as a luminescence thermometry probe. The choice is commonly made on quantum dots, organic dyes, metal-organic complexes and frameworks, and lanthanide or transition metal ion based phosphors, the last of which are the most exploited ones. When screening materials for the suitable luminescence thermometry probe for the specific application, attention is given to material's structural, chemical, luminescent, and thermographic properties. Most of all, luminescence of material should notably change with temperature to provide sensitive measurement with adequate temperature resolution. Also, a probe should provide repeatable and reproducible temperature determination. Furthermore, for the practical realization of thermometer, some other materials properties are of interest, such as excitation and emission wavelengths and bandwidths, which should facilitate production of cost-effective and simple measurement devices.Regarding structural and chemical properties, lanthanide and transition metal ion based materials and material's systems meet most of above mentioned conditions. They are thermally and chemically stable, provide sufficient brightness, and exceptional photostability. They also facilitate thermometry with excellent repeatability and reproducibility. However, they generally lack sensitivity and, consequently, temperature resolution. LIR readout scheme with trivalent lanthanide ion activated phosphors exploits emissions from two closely separated and thermally coupled excited states (either in the upconversion or downshifting processes). [3] In such case, the relative sensitivity is limited by the energy difference between these excitedThe binary luminescence thermometry probe is prepared from Y 2 O 3 :Ho 3+ and Mg 2 TiO 4 :Mn 4+ powders. This probe facilitates self-referencing temperature readouts with excellent repeatability from both emission intensity ratio and excited state lifetimes. The ratio of intensities of Mn 4+ deep red emission from 2 E, 4 T 2 → 4 A 2 electronic transitions, and Ho 3+ green emission from 5 F 4 , 5 S 2 → 5 I 8 electronic transitions provides temperature measurements over the room temperature to 100 °C temperature range with a superior relative sensitivity of 4.6% °C −1 and temperature resolution of 0.1 °C. Over the same temperature range, the tem...
Synthesis, structure, morphology, and detailed spectroscopic and crystal-field analysis of Mn4+ doped Mg2TiO4 nanoparticles (NPs) are presented. These Mg2TiO4:Mn4+ NPs are obtained through a Pechini-type polymerized complex route and calcination at 600 °C, and are approximately 10 nm in diameter and loosely agglomerated into 1-μm particles, as evidenced from transmission electron microscopy. These NPs exhibit strong, sharp red emission at 658 nm (with a 1.2 ms emission decay) as a result of the spin-forbidden 2Eg → 4A2g electron transition of the tetravalent manganese ions. No signatures of the presence of manganese ions in divalent or trivalent valence states are observed in the NPs with either photoluminescence or diffuse reflection spectroscopy. The energy levels of the Mn4+ ions in a trigonal crystal field of Mg2TiO4 are calculated using the exchange-charge model and are well matched with the experimental photoluminescence excitation and emission spectra. The absolute values of the calculated crystal-field parameters (CFPs) are similar to those reported for trigonal point symmetry at Mn4+ dopant sites (Y2Ti2O7, Y2Sn2O7, and Na2SiF6). It is also observed that the contributions of covalent and exchange effects to the CFPs are nearly eight times greater than the point-charge contribution.
The addition of heteroatoms to pristine carbon quantum dots (CQDs) change their structure and optical properties. In this study, fluorine (F)- and chlorine (Cl)-doped CQDs are prepared by the one-step green hydrothermal route from sodium fluoride, sodium chloride, urea, and citric acid as the starting precursors. Microscopy analysis reveals that the average size of these quantum dots is 5 ± 2 nm, whereas the chemical study shows the existence of C–F and C–Cl bonds. The produced F- and Cl-doped CQDs have fluorescence quantum yields of 0.151 and 0.284, respectively, at an excitation wavelength of 450 nm. Charge transfer resistance of F- and Cl-doped CQDs films is 2 orders of magnitude higher than in the pristine CQD films. Transport band gap of the doped CQDs is 2 eV bigger than that of pristine CQDs. Radical scavenging activity shows very good antioxidant activity of doped CQDs. Antibacterial testing reveals poor antibacterial activity against Staphylococcus aureus and Escherichia coli. The F- and Cl-doped CQDs are successfully used as fluorescent probes for cell imaging as shown by confocal microscopy.
Herein, temperature dependencies of emission and emission decay of Zn2SiO4:Mn2+ powder in the range from room temperature to 300 °C is reported. These dependencies allow temperature sensing from luminescence measurements, since Mn2+ emission intensity, emission band spectral position, and emission decay are rapidly changing over the entire temperature range. For fluorescence intensity ratio method, measurement that relays on emission intensity changes with temperature, sensitivity of 12.2% is found. In the case of lifetime thermometry, method that relays on emission decay changes with temperature, sensitivity of 0.48% is determined. Both sensitivity values are among the highest ever recorded for inorganic materials.
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