Nanoscale biocompatible photoluminescence (PL) thermometers that can be used to accurately and reliably monitor intracellular temperatures have many potential applications in biology and medicine. Ideally, such nanothermometers should be functional at physiological pH across a wide range of ionic strengths, probe concentrations, and local environments. Here, we show that water-soluble N,S-co-doped carbon dots (CDs) exhibit temperature-dependent photoluminescence lifetimes and can serve as highly sensitive and reliable intracellular nanothermometers. PL intensity measurements indicate that these CDs have many advantages over alternative semiconductor- and CD-based nanoscale temperature sensors. Importantly, their PL lifetimes remain constant over wide ranges of pH values (5-12), CD concentrations (1.5 × 10 to 0.5 mg/mL), and environmental ionic strengths (up to 0.7 mol·L NaCl). Moreover, they are biocompatible and nontoxic, as demonstrated by cell viability and flow cytometry analyses using NIH/3T3 and HeLa cell lines. N,S-CD thermal sensors also exhibit good water dispersibility, superior photo- and thermostability, extraordinary environment and concentration independence, high storage stability, and reusability-their PL decay curves at temperatures between 15 and 45 °C remained unchanged over seven sequential experiments. In vitro PL lifetime-based temperature sensing performed with human cervical cancer HeLa cells demonstrated the great potential of these nanosensors in biomedicine. Overall, N,S-doped CDs exhibit excitation-independent emission with strongly temperature-dependent monoexponential decay, making them suitable for both in vitro and in vivo luminescence lifetime thermometry.

Noninvasive lanthanide‐doped optical thermometers based on fluorescent intensity ratio (FIR) technique have emerged as promising noncontact tools for detecting the inaccessible objects at different scales. Currently, the theoretical and experimental investigations of various influential factors on thermal performances of luminescence thermometers have become one of the hotspots to develop highly sensitive optical thermometers. On the other hand, near‐infrared (NIR) light‐responsive nanothermometers with deep‐tissue penetration have been widely applied for subcutaneous and intracellular thermometry, which could be integrated with optical heating and imaging functions to construct all‐in‐one thermometer‐heater platforms for cancer diagnosis and therapy. In this review, the recent advances in luminescence thermometry based on the thermally coupled levels (TCLs) are elaborately introduced from fundamental aspects to possible biomedical applications, with the perspective and outlook in the emerging challenges of FIR thermometers applied in biomedical science.

Chemical exchange saturation transfer (CEST) MRI is sensitive to dilute proteins and peptides as well as microenvironmental properties. However, the complexity of the CEST MRI effect, which varies with the labile proton content, exchange rate and experimental conditions, underscores the need for development of quantitative CEST (qCEST) analysis. Towards this goal, it has been shown that the omega plot is capable of quantifying paramagnetic CEST (PARACEST) MRI. However, the use of omega plot is somewhat limited for diamagnetic CEST (DIACEST) MRI because it is more susceptible to direct RF saturation (spillover) effects owing to their relatively small chemical shift. Recently, it has been found that for dilute DIACEST agents that undergo slow to intermediate chemical exchange, the RF spillover effect varies little with the labile proton ratio and exchange rate. Therefore, we postulated that the omega plot analysis can be improved if RF spillover effect could be estimated and taken into account. Specifically, simulation showed that both labile proton ratio and exchange rate derived using the spillover effect-corrected omega plot are in good agreement with simulated values. In addition, the modified omega plot was confirmed experimentally, and we showed that the derived labile proton ratio increases linearly with creatine concentration (P< 0.01), with little difference in their exchange rate (P=0.32). In summary, our study extended the conventional omega plot for quantitative analysis of DIACEST MRI.

Monochrome LEDs and color graphical patterns were fabricated by changing the thickness and doping concentration of carbon dot layers.

In a line with most recent trends in developing non-toxic fluorescent nanomaterials, we combined blue emissive carbon dots with green and red emissive zinc copper indium sulfide (ZCIS) core/shell quantum dots (QDs) to achieve white light-emitting diodes (WLEDs) with a high color rendering index of 93. This indicates that ZCIS QDs, with their broad emission bands, can be employed to effectively make up the emission of carbon dots in the yellow and red regions to produce WLEDs in the wide region of color temperature by tuning the volume ratio of these constituting luminophores. Their electroluminescence characteristics including color rendering index, Commission Internationale de l'Eclairage (CIE) color coordinates, and color temperatures were evaluated as a function of forward current. The CIE-1931 chromaticity coordinates of the as-prepared WLEDs, exhibiting good stability, were slightly shifted from (0.321, 0.312) at 10 mA to (0.351, 0.322) at 30 mA, which was mainly caused by the different thermal quenching coefficients of carbon dots and ZCIS QDs.

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The external quantum efficiencies (EQEs) of perovskite quantum dot lightemitting diodes (QD-LEDs) are close to the out-coupling efficiency limitation. However, these high-performance QD-LEDs still suffer from a serious issue of efficiency roll-off at high current density. More injected carriers produce photons less efficiently, strongly suggesting the variation of ratio between radiative and non-radiative recombination. An approach is proposed to balance the carrier distribution and achieve high EQE at high current density. The average interdot distance between QDs is reduced and this facilitates carrier transport in QD films and thus electrons and holes have a balanced distribution in QD layers. Such encouraging results augment the proportion of radiative recombination, make devices with peak EQE of 12.7%, and present a great device performance at high current density with an EQE roll-off of 11% at 500 mA cm −2 (the lowest roll-off known so far) where the EQE is still over 11%.their PL QYs. Diverse approaches have been proposed to boost the performance of QD-LEDs via surface passivation, [19] modification of carrier transport layer, [20][21][22] and anion exchange. [12] QD-LEDs have therefore demonstrated an impressive quick increase of peak external quantum efficiencies (EQEs) from 0.01% to 21.3% within 4 years, suggesting perovskite QDs as promising new-generation optoelectronic semiconductor materials. [6,7,12,21] In spite of the rapid development of perovskite QD-LEDs, at present, the EQEs of these devices tend to be acquired at low current density and manifest significant loss at higher current density, which is known as efficiency roll-off. In best-performed perovskite QD-LEDs, [12] the maximum EQE was obtained at a current density lower than 1 mA cm −2 ; when the current density reached 100 mA cm −2 , the EQE became only about 1%, indicating the efficiency loss reached 95%. Such efficiency loss actually limits achievable brightness and leads to excessive power consumption.Apart from perovskite QD-LEDs, perovskite film-LEDs present similar issues and recently, a few studies have come up with several methods to minimize EQE droop. Zou et al. and Yang et al. concluded that it was luminescence quenching caused by Auger recombination that was responsible for the efficiency roll-off. [23,24] To reduce carrier density in quantum wells (QWs), increased QW width was acquired via different

ZnO based oxide system Zn1−x−yBexMgyO has been prepared by pulsed laser deposition. By incorporating different amounts of beryllium and magnesium into ZnO, the bandgap of ZnBeMgO has been modulated from 3.7 to 4.9 eV continuously. The crystal quality of ZnBeMgO film has been improved significantly comparing with that of either ZnMgO or BeZnO. These ZnBeMgO films are promising for fabricating high-efficiency optoelectronic devices such as solar-blind UV detectors.