Multicolor laser oscillation in a single self-assembled colloidal quantum dot microsphere

Self-assembled microsphere lasers oscillating simultaneously at more than one wavelength in the visible are reported. The lasers consist of micron-scale supraparticles made of CdSxSe1-x/ ZnS quantum dots that emit between 585-605 nm and 625-655 nm

Water resistant caesium lead bromide crystal composites

Water-resistant luminescent polymer composites with CsPbBr3 quantum dots in Cs4PbBr6 crystals (CsPbBr3@Cs4PbBr6) are reported. These color-converting materials enable a narrow-band green emission with fast dynamics and are therefore a potential alternative to phosphors, mainly for applications that require a fast modulation of light

Crowdsourcing-Based Fingerprinting for Indoor Location in Multi-Storey Buildings

POCI-01-0247-FEDER-033479The number of available indoor location solutions has been growing, however with insufficient precision, high implementation costs or scalability limitations. As fingerprinting-based methods rely on ubiquitous information in buildings, the need for additional infrastructure is discarded. Still, the time-consuming manual process to acquire fingerprints limits their applicability in most scenarios. This paper proposes an algorithm for the automatic construction of environmental fingerprints on multi-storey buildings, leveraging the information sources available in each scenario. It relies on unlabelled crowdsourced data from users’ smartphones. With only the floor plans as input, a demand for most applications, we apply a multimodal approach that joins inertial data, local magnetic field andWi-Fi signals to construct highly accurate fingerprints. Precise movement estimation is achieved regardless of smartphone usage through Deep Neural Networks, and the transition between floors detected from barometric data. Users’ trajectories obtained with Pedestrian Dead Reckoning techniques are partitioned into clusters with Wi-Fi measurements. Straight sections from the same cluster are then compared with subsequence Dynamic Time Warping to search for similarities. From the identified overlapping sections, a particle filter fits each trajectory into the building’s floor plans. From all successfully mapped routes, fingerprints labelled with physical locations are finally obtained. Experimental results from an office and a university building show that this solution constructs comparable fingerprints to those acquired manually, thus providing a useful tool for fingerprinting-based solutions automatic setup.publishersversionpublishe

Surface functionalisation of self-assembled quantum dot microlasers with a DNA aptamer

Surface functionalisation of self-assembled colloidal quantum dot supraparticle lasers with a Thrombin Binding Aptamer (TBA-15) has been demonstrated. Self-assembly of CdSSe/ZnS alloyed core/shell microsphere-shape CQD supraparticles emitting at 630 nm was carried out using an oil-in-water emulsion technique, yielding microspheres with an oleic acid surface and an average diameter of 7.3 ± 5.3 μm. Surface modification of the microspheres was achieved through a ligand exchange with mercaptopropionic acid and subsequent attachment of TBA-15 using EDC/NHS coupling, confirmed by zeta potential and Fourier Transform IR spectroscopy. Lasing functionality between 627 nm and 635 nm was retained post-functionalisation with oleic acid- and TBA-coated microspheres exhibiting laser oscillation with thresholds as low as 4.10 ± 0.37 mJ.cm-2 and 7.23 ± 0.78 mJ.cm-2 respectively

Self-assembled semiconductor microlaser based on colloidal nanoplatelets

A semiconductor microsphere laser based on colloidal nanoplatelets is demonstrated comprising a micron-sized supraparticle obtained by self-assembly of core/shell CdSe/ CdS nanoplatelets with peak luminescence at 660nm. It shows multimode laser emission between 665 and 695nm with threshold at 200 nJ (28 ± 17 mJ.cm -2 )

Biotinylated photocleavable semiconductor colloidal quantum dot supraparticle microlaser

Luminescent supraparticles of colloidal semiconductor nanocrystals can act as microscopic lasers and are hugely attractive for biosensing, imaging, and drug delivery. However, biointerfacing these to increase functionality while retaining their main optical properties remains an unresolved challenge. Here, we propose and demonstrate red-emitting, silica-coated CdS xSe 1−x/ZnS colloidal quantum dot supraparticles functionalized with a biotinylated photocleavable ligand. The success of each step of the synthesis is confirmed by scanning electron microscopy, energy dispersive X-ray and Fourier transform infrared spectroscopy, ζ-potential, and optical pumping measurements. The capture and release functionality of the supraparticle system is proven by binding to a neutravidin functionalized glass slide and subsequently cleaving off after UV-A irradiation. The biotinylated supraparticles still function as microlasers; e.g., a 9 μm diameter supraparticle has oscillating modes around 625 nm at a threshold of 58 mJ/cm 2. This work is a first step toward using supraparticle lasers as enhanced labels for bionano applications

Biotinylated photocleavable semiconductor colloidal quantum dot supraparticle microlaser

Luminescent supraparticles of colloidal semiconductor nanocrystals can act as microscopic lasers and are hugely attractive for biosensing, imaging, and drug delivery. However, biointerfacing these to increase functionality while retaining their main optical properties remains an unresolved challenge. Here, we propose and demonstrate red-emitting, silica-coated CdSxSe1−x/ZnS colloidal quantum dot supraparticles functionalized with a biotinylated photocleavable ligand. The success of each step of the synthesis is confirmed by scanning electron microscopy, energy dispersive X-ray and Fourier transform infrared spectroscopy, ζ-potential, and optical pumping measurements. The capture and release functionality of the supraparticle system is proven by binding to a neutravidin functionalized glass slide and subsequently cleaving off after UV-A irradiation. The biotinylated supraparticles still function as microlasers; e.g., a 9 μm diameter supraparticle has oscillating modes around 625 nm at a threshold of 58 mJ/cm2. This work is a first step toward using supraparticle lasers as enhanced labels for bionano applications

Colloidal semiconductor quantum well supraparticles as low-threshold and photostable microlasers

This study introduces and compares the lasing performance of micron-sized and sphere-shaped supraparticle (SP) lasers fabricated through bottom-up assembly of II-VI semiconductor colloidal quantum wells (CQWs) with their counterparts made of quantum dots (CQDs). CQWs consist of a 4-monolayers thick CdSe core and an 8-monolayers thick CdxZn1-xS shell with a nominal size of 14 × 15 × 4.2 nm, and CQDs of CdSxSe1-x/ZnS with 6 nm diameter. SPs are optically characterized with a 0.76 ns pulse laser (spot size: 2.88 × 10−7 cm2) at 532 nm, and emit in the 620–670 nm spectral range. Results show that CQW SPs have lasing thresholds twice as low (0.1–0.3 nJ) as CQD SPs (0.3–0.6 nJ), and stress tests using a constant 0.6 nJ optical pump energy demonstrate that CQW SPs withstand lasing emission for longer than CQD SPs. Lasing emission in CQW and CQD SPs under continuous operation yields half-lives of τCQW SP ≈150 min and τCQD SP ≈22 min, respectively. The half-life of CQW SPs is further extended to τQW ≈385 min when optically pumped at 0.5 nJ. Such results compare favorably to those in the literature and highlight the performance of CdSe-based CQW SPs for laser applications

Waveguide-integrated colloidal nanocrystal supraparticle lasers

Supraparticle (SP) microlasers fabricated by the self-assembly of colloidal nanocrystals have great potential as coherent optical sources for integrated photonics. However, their deterministic placement for integration with other photonic elements remains an unsolved challenge. In this work, we demonstrate the manipulation and printing of individual SP microlasers, laying the foundation for their use in more complex photonic integrated circuits. We fabricate CdSxSe1−x/ZnS colloidal quantum dot (CQD) SPs with diameters from 4 to 20 μm and Q-factors of approximately 300 via an oil-in-water self-assembly process. Under a subnanosecond-pulse optical excitation at 532 nm, the laser threshold is reached at an average number of excitons per CQD of 2.6, with modes oscillating between 625 and 655 nm. Microtransfer printing is used to pick up individual CQD SPs from an initial substrate and move them to a different one without affecting their capability for lasing. As a proof of concept, a CQD SP is printed on the side of an SU-8 waveguide, and its modes are successfully coupled to the waveguide