We demonstrate using single molecule spectroscopy that inorganic CsPbI3 perovskite quantum dots (PQDs) undergo an irreversible, photoaccelerated reaction with water that results in a blue-shift of the photoluminescence (PL) and ultimately to complete quenching of the emission. We find that decomposition does not take place in the presence of oxygen alone but that it requires light and water. We also analyze the blinking for some stable PQDs and find a continuous distribution of emission states with a linear correlation between intensity and lifetime. We postulate that, in addition to charging and discharging processes, blinking arises from the activation and deactivation of nonradiative recombination centers in the PQDs.

Quantum sensors based on solid-state spins provide tremendous opportunities in a wide range of fields from basic physics and chemistry to biomedical imaging. However, integrating them into a scanning probe microscope to enable practical, nanoscale quantum imaging is a highly challenging task. Recently, the use of single spins in diamond in conjunction with atomic force microscopy techniques has allowed significant progress towards this goal, but generalisation of this approach has so far been impeded by long acquisition times or by the absence of simultaneous topographic information. Here we report on a scanning quantum probe microscope which solves both issues, by employing a nano-spin ensemble hosted in a nanodiamond. This approach provides up to an order of magnitude gain in acquisition time, whilst preserving sub-100 nm spatial resolution both for the quantum sensor and topographic images. We demonstrate two applications of this microscope. We first image nanoscale clusters of maghemite particles through both spin resonance spectroscopy and spin relaxometry, under ambient conditions. Our images reveal fast magnetic field fluctuations in addition to a static component, indicating the presence of both superparamagnetic and ferromagnetic particles. We next demonstrate a new imaging modality where the nano-spin ensemble is used as a thermometer. We use this technique to map the photo-induced heating generated by laser irradiation of a single gold nanoparticle in a fluid environment. This work paves the way towards new applications of quantum probe microscopy such as thermal/magnetic imaging of operating microelectronic devices and magnetic detection of ion channels in cell membranes.In recent years, quantum sensing has attracted increasing attention because it opens up the possibilities for non-invasive sensing with nanoscale mapping potential and single atom sensitivity. The model system for these studies has been the negatively charged nitrogen-vacancy (NV) centre in diamond, which has shown great promise as an atomic-sized sensor operating under ambient conditions [1][2][3]. The NV centre is a photostable point defect whose electronic ground state is a spin triplet that can be initialised and read out by optical means [4,5]. This makes it possible to detect the spin resonance of a single NV centre and coherently control its spin state. Owing to interaction with the local environment, measurement of the spectral and temporal properties of an NV centre's spin provides access to a number of local properties, such as the magnetic field, electric field, pressure or temperature [6][7][8][9][10]. Furthermore, NV sensors are capable not only of measuring static fields but also fluctuating ones. This, in turn, allows retrieval of spectral information from a sample [11][12][13][14][15][16]. This capability was recently used to perform nuclear magnetic resonance spectroscopy on a small ensemble of protons [17,18].In order to obtain spatial information about the sample's properties, the NV probe must be scanned relative ...

Hydrophobic forces play a key role in the processes of collapse and reswelling of thermoresponsive polymers. However, little is known about the dynamics of these processes. Here, thermoresponsive poly(N-isopropylacrylamide)-encapsulated gold nanoparticles (Au-PNIPAM) are heated via nanosecond laser flash photolysis. Photothermal heating via excitation of the localized surface plasmon resonance of the Au nanoparticle cores results in rapid PNIPAM shell collapse within the 10 ns pulse width of the laser. Remarkably, reswelling of the polymer shell takes place in less than 100 ns. A clear pump fluence threshold for the collapse of the PNIPAM shell is demonstrated, below which collapse is not observed. Reswelling takes longer at higher laser intensities.

Copper zinc tin sulfide (CZTS) nanocrystal inks are promising candidates for the development of cheap, efficient, scalable, and nontoxic photovoltaic (PV) devices. However, optimization of the synthetic chemistry to achieve these goals remains a key challenge. Herein we describe a single-step, aqueous-based synthesis that yields high-quality CZTS nanocrystal inks while also minimizing residual organic impurities. By exploiting simultaneous redox and crystal formation reactions, square-platelet-like CZTS nanocrystals stabilized by SnS and thiourea are produced. The CZTS synthesis is optimized by using a combination of inductively coupled plasma analysis, Raman spectroscopy, Fourier transform infrared spectroscopy, and synchrotron powder X-ray diffraction to assess the versatility of the synthesis and identify suitable composition ranges for achieving phase-pure CZTS. It is found that mild heat treatment between 185 and 220 °C is most suitable for achieving this because this temperature range is sufficiently high to thermalize existing ligands and ink additives while minimizing tin loss, which is problematic at higher temperatures. The low temperatures required to process these nanocrystal inks to give CZTS thin films are readily amenable to production-scale processes.

Copper zinc tin selenide (CZTSe) nanocrystal inks show promise as a candidate for developing cheap, scalable, efficient, and nontoxic photovoltaic devices. They also present an important opportunity to controllably mix copper zinc tin sulfide (CZTS) with CZTSe to produce directly spectrally tunable Cu 2 ZnSn(S/Se) 4 (CZTSSe) solid-solutions using low-temperature processes. Herein, we describe a one-pot, low-temperature, aqueous-based synthesis that employs simultaneous redox and crystal formation reactions to yield CZTSe nanocrystal inks stabilized by Sn 2 Se 7 6− and thiourea. This versatile CZTSe synthesis is understood through the use of inductively coupled plasma mass spectrometry, Raman spectroscopy, Fourier transform infrared spectroscopy, and powder X-ray diffraction. It is further shown that stoichiometrically mixed CZTSe and CZTS nanocrystal powders yield a single CZTSSe phase at annealing temperatures between 200 and 250 °C. This facile and low-temperature process offers a low-energy alternative for the deposition of pure CZTSe/SSe thin films and enables the band gap to be readily tuned from 1.5 down to 1.0 eV by simple solution chemistry.