control, [4] luminescence thermometry (LTh) is rapidly expanding. In this case, thermal sensing is based on the appropriate analysis of temperature-dependent luminescence, leading to the appearance of Luminescent Nanothermometers (LNThs). [5] The main limitations of LNThs include: (i) the reading of temperatureinduced changes in the luminescence intensity from single emission lines and (ii) the short penetration depths of LNThs operating in the visible range [6] for in vivo applications along with autofluorescence background signals. [7] The former can be overcome by the use of ratiometric-based LNThs (hereafter RLNThs), [5a] in which the readout is extracted from the ratio between their photoluminescence (PL) intensity at different wavelengths, and the latter requires the use of NPs working in the near-infrared range (NIR), in particular in the second biological window (II-BW), expanding from 1000 to 1350 nm. [6b,8] Some examples of RLNThs working in the II-BW include singly and doubly rare earth doped NPs (RE-NPs) or the combination, in a single structure, of both RE-NPs and semiconductor quantum dots (QDs). [5c,9] In the case of rare earth doped NPs, their thermal sensitivity is lower than 0.5% °C −1 and the reduced absorption cross sections per NP leads to low signal-to-noise ratios during in vivo experiments. The combination of these two factors results in thermal Temperature sensing in biological media (cells, tissues, and living organisms) has become essential in the development of the last generation of diagnostics and therapeutic strategies. Thermometry can be used for early detection of different diseases, such as cancer, stroke, or inflammation processes, one of whose incipient symptoms is the appearance of localized temperature singularities. Luminescence nanothermometry, as a tool to accurately provide temperature sensing in biological media, requires the rational design and development of nanothermometers operating in the second biological window. In this work, this is achieved using Ag/Ag 2 S nanocrystals as multiparametric thermal sensing probes. Temperature sensing with remarkably high sensitivity (4% °C −1 ) is possible through intensity-based measurements, as their infrared emission is strongly quenched by small temperature variations within the biological range (15-50 °C). Heating also results in a remarkable redshift of the emission band, which allows for concentrationindependent temperature sensing based on infrared ratiometric measurements, with thermal sensitivity close to 2% °C −1 . These results make Ag/Ag 2 S nanocrystals the most sensitive among all noncomposite nanothermometers operating in the second biological window reported so far, allowing for deeptissue temperature measurements with low uncertainty (0.2 °C).

SiO2 encapsulation of alloyed CdSeZnS nanocrystals (NCs) shows differences in terms of optical properties and luminescence quantum yield, depending on the surface composition, size, and ligand content. In this work, emphasis has been placed on the fine control required to obtain luminescent SiO2 encapsulated NCs by studying the role of oleic acid (OA), stearic acid (SA), and dodecanethiol (DDT) ligands on the alloyed NCs. While the use of anchored DDT molecules is essential to preserve the optical properties, intercalated OA and SA play a critical role for SiO2 nucleation, as stated by 1H NMR (including DOSY and NOESY) spectroscopy. These results emphasize the importance of surface chemistry in NCs; it is crucial to control their reactivity, and therefore their impact, in different applications, from optics to biomedicine.

Halide ions cap and stabilize colloidal semiconductor nanocrystal (NC) surfaces allowing for NCs surface interactions that may improve the performance of NC thin film devices such as photo-detectors and/or solar cells. Current ways to introduce halide anions as ligands on surfaces of NCs produced by the hot injection method are based on post-synthetic treatments. In this work we explore the possibility to introduce Cl in the NC ligand shell in situ during the NCs synthesis. With this aim, the effect of 1,2-dichloroethane (DCE) in the synthesis of CdSe rod-like NCs produced under different Cd/Se precursor molar ratios has been studied. We report a double role of DCE depending on the Cd/Se precursor molar ratio (either under excess of cadmium or selenium precursor). According to mass spectrometry (ESI-TOF) and nuclear magnetic resonance ((1)H NMR), under excess of Se precursor (Se dissolved in trioctylphosphine, TOP) conditions at 265 °C ethane-1,2-diylbis(trioctylphosphonium)dichloride is released as a product of the reaction between DCE and TOP. According to XPS studies chlorine gets incorporated into the CdSe ligand shell, promoting re-shaping of rod-like NCs into pyramidal ones. In contrast, under excess Cd precursor (CdO) conditions, DCE reacts with the Cd complex releasing chlorine-containing non-active species which do not trigger NCs re-shaping. The amount of chlorine incorporated into the ligand shell can thus be controlled by properly tuning the Cd/Se precursor molar ratio.

The trade-off between photobrightening and photobleaching controls the emission stability of colloidal quantum dots. This balance is critical in optical trapping configurations, where irradiances that confine and simultaneously excite the nanocrystals in the focal region cannot be indefinitely lowered. In this work, we studied the photobrightening and bleaching behaviors of two types of silica-encapsulated quantum dots excited upon two-photon absorption in an optical trap. The first type consists of alloyed CdSeZnS quantum dots covered with a silica shell. We found that the dynamics of these as-prepared architectures are similar to those previously reported for bare surface-deposited quantum dots, where thousands of times smaller irradiances were used. We then analyzed the same quantum dot systems treated with an extra intermediate sulfur passivating shell for the better understanding of the surface traps influence in the temporal evolution of their emission in the optical trap. We found that these latter systems exhibit better homogeneity in their photodynamic behavior compared to the untreated ones. These features strengthen the value of quantum dot preparations in optical manipulation as well as for applications where both long and maximal emission stability in physiological and other polar media are required.