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 )

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

Colloidal semiconductor nanocrystals for colour conversion and self-assembled lasers

Error on title page. Date of award is 2023.Nanocrystals have been at the forefront of technological developments in photonics thanks to their unique optoelectronic properties. In this thesis, different types of luminescent semiconductor nanocrystals have been studied, improved, and implemented towards novel applications. The topics of research discussed are: (i) II-V colloidal quantum dots as the building blocks of novel lasers via self-assembly from the bottom up (the fabrication and study of these are in fact the main focus of the thesis), and (ii) a perovskite quantum dot-based structure as a robust colour-converter of LEDs. (i) II-VI alloyed core-shell CdxS1-xSe/ZnS quantum dots are nanosized colloids (dispersed in solution) with excellent optical properties in the visible spectrum. These Cd-based colloidal quantum dots represent the most mature colloidal quantum dot technology and their use as light emitters and laser gain material is being intensely pursued. To date, colloidal quantum dot (and related nanocrystal) lasers have been made from the top down with the quantum dots deposited into an optical resonator fabricated separately. Departing from this standard approach and fully capitalizing on the solution processability of colloids, this work uses quantum dots as nanobricks to create supracrystal/supraparticle microspheres that self-assemble from a bottom-up approach. These supraparticles act simultaneously as the gain material and the optical microcavity. In addition to that they are capable of laser emission under optical excitation. Using red-emitting CdxS1-xSe/ZnS quantum dots, laser oscillation between the 625 and the 655 nm is obtained from single quantum dot spheres with diameters of 5.6 ± 3.2 μm and energy threshold of 4.7 ± 2.1 nJ for a 532 nm pump source with a beam spot size of approximately 6 μm in diameter. The possibility of making hetero-supraparticles by selecting and self-assembling together quantum dots with different emission and absorption spectra is also demonstrated. When carefully selected, these combinations can enhance the quality factor of the sphere. As an example, microspheres of red quantum dots and green quantum dots had an increase in the quality factor from 135±19 to 340±60, when compared to red quantum dot microspheres of the same size (6.0 ± 0.5 μm in diameter). Microspheres with quantum dots of red and higher band gap species also maintain similar laser threshold energies to their red quantum dot microsphere counterparts. In the example mentioned above, both microspheres reached laser threshold at 12 – 14 mJ.cm-2, for a beam spot size of 2.88×10-7 cm2. In addition to that, microspheres with higher bandgap quantum dots in their composition have also reported laser for cavities of sizes 3 – 4 times bigger, further suggesting that the increase in the quality factor and decrease in self-absorption is promoted by the addition of higher bandgap quantum dots. Synthesis of microspheres with different bandgap quantum dots also allow for simultaneous multicolor lasing in a single sphere. Stable dual laser emission of yellow (575 nm) and red (630 nm) is shown in a microsphere of 6.0 ± 0.5 μm in diameter, for energy thresholds between 13.3 and 45.6 nJ and for a spot size of approximately 4.85 × 10-7 cm2. The integration of supraparticle lasers to other devices is demonstrated via transfer printing. This method can move them reliably between substrates, and this was done to successfully couple them to waveguides. This demonstration paves the way to more complex designs and applications in integrated photonics. In addition to quantum dots, the self-assembly procedure was also tested and adapted to other types of semiconductor nanocrystals, including nanoplatelets and tetrapods, in a collaboration work with Nanyang Technological University (LUMINOUS! group). (ii) A different material was studied for colour conversion. Ceasium lead bromide perovskite nanocrystals have up to date the fastest luminescent dynamics of all known nanocrystals and are therefore appealing for light communication applications. However, they are not stable in the presence of heat and humidity. Different coatings using two different polymers (PDMS and PMMA) have been studied as a way of protecting and increasing the stability of CsPbBr3@Cs4PbBr6 crystals. While PDMS samples were not stable upon immersion in water, PMMA composites showed little to no trace of degradation when immersed in water under vigorous stirring for up to 72 hours. Bandwidth measurements with PMMA samples have given similar results to the current state of the art, showing that PMMA is an effective matrix host for CsPbBr3@Cs4PbBr6 against moisture and water.Nanocrystals have been at the forefront of technological developments in photonics thanks to their unique optoelectronic properties. In this thesis, different types of luminescent semiconductor nanocrystals have been studied, improved, and implemented towards novel applications. The topics of research discussed are: (i) II-V colloidal quantum dots as the building blocks of novel lasers via self-assembly from the bottom up (the fabrication and study of these are in fact the main focus of the thesis), and (ii) a perovskite quantum dot-based structure as a robust colour-converter of LEDs. (i) II-VI alloyed core-shell CdxS1-xSe/ZnS quantum dots are nanosized colloids (dispersed in solution) with excellent optical properties in the visible spectrum. These Cd-based colloidal quantum dots represent the most mature colloidal quantum dot technology and their use as light emitters and laser gain material is being intensely pursued. To date, colloidal quantum dot (and related nanocrystal) lasers have been made from the top down with the quantum dots deposited into an optical resonator fabricated separately. Departing from this standard approach and fully capitalizing on the solution processability of colloids, this work uses quantum dots as nanobricks to create supracrystal/supraparticle microspheres that self-assemble from a bottom-up approach. These supraparticles act simultaneously as the gain material and the optical microcavity. In addition to that they are capable of laser emission under optical excitation. Using red-emitting CdxS1-xSe/ZnS quantum dots, laser oscillation between the 625 and the 655 nm is obtained from single quantum dot spheres with diameters of 5.6 ± 3.2 μm and energy threshold of 4.7 ± 2.1 nJ for a 532 nm pump source with a beam spot size of approximately 6 μm in diameter. The possibility of making hetero-supraparticles by selecting and self-assembling together quantum dots with different emission and absorption spectra is also demonstrated. When carefully selected, these combinations can enhance the quality factor of the sphere. As an example, microspheres of red quantum dots and green quantum dots had an increase in the quality factor from 135±19 to 340±60, when compared to red quantum dot microspheres of the same size (6.0 ± 0.5 μm in diameter). Microspheres with quantum dots of red and higher band gap species also maintain similar laser threshold energies to their red quantum dot microsphere counterparts. In the example mentioned above, both microspheres reached laser threshold at 12 – 14 mJ.cm-2, for a beam spot size of 2.88×10-7 cm2. In addition to that, microspheres with higher bandgap quantum dots in their composition have also reported laser for cavities of sizes 3 – 4 times bigger, further suggesting that the increase in the quality factor and decrease in self-absorption is promoted by the addition of higher bandgap quantum dots. Synthesis of microspheres with different bandgap quantum dots also allow for simultaneous multicolor lasing in a single sphere. Stable dual laser emission of yellow (575 nm) and red (630 nm) is shown in a microsphere of 6.0 ± 0.5 μm in diameter, for energy thresholds between 13.3 and 45.6 nJ and for a spot size of approximately 4.85 × 10-7 cm2. The integration of supraparticle lasers to other devices is demonstrated via transfer printing. This method can move them reliably between substrates, and this was done to successfully couple them to waveguides. This demonstration paves the way to more complex designs and applications in integrated photonics. In addition to quantum dots, the self-assembly procedure was also tested and adapted to other types of semiconductor nanocrystals, including nanoplatelets and tetrapods, in a collaboration work with Nanyang Technological University (LUMINOUS! group). (ii) A different material was studied for colour conversion. Ceasium lead bromide perovskite nanocrystals have up to date the fastest luminescent dynamics of all known nanocrystals and are therefore appealing for light communication applications. However, they are not stable in the presence of heat and humidity. Different coatings using two different polymers (PDMS and PMMA) have been studied as a way of protecting and increasing the stability of CsPbBr3@Cs4PbBr6 crystals. While PDMS samples were not stable upon immersion in water, PMMA composites showed little to no trace of degradation when immersed in water under vigorous stirring for up to 72 hours. Bandwidth measurements with PMMA samples have given similar results to the current state of the art, showing that PMMA is an effective matrix host for CsPbBr3@Cs4PbBr6 against moisture and water

Enhancing self-assembled colloidal quantum dot microsphere lasers

We demonstrate the superior emission properties of a red-emitting self-assembled quantum dot microsphere laser made from a blend of green and red bandgap CdS x Se 1-x / ZnS quantum dots. The addition of the higher bandgap material reduces self-absorption and improves the Q-factor

Multifunctional microfluidic chip for optical nanoprobe based RNA detection – application to Chronic Myeloid Leukemia

Abstract Many diseases have their treatment options narrowed and end up being fatal if detected during later stages. As a consequence, point-of-care devices have an increasing importance for routine screening applications in the health sector due to their portability, fast analyses and decreased cost. For that purpose, a multifunctional chip was developed and tested using gold nanoprobes to perform RNA optical detection inside a microfluidic chip without the need of molecular amplification steps. As a proof-of-concept, this device was used for the rapid detection of chronic myeloid leukemia, a hemato-oncological disease that would benefit from early stage diagnostics and screening tests. The chip passively mixed target RNA from samples, gold nanoprobes and saline solution to infer a result from their final colorimetric properties. An optical fiber network was used to evaluate its transmitted spectra inside the chip. Trials provided accurate output results within 3 min, yielding signal-to-noise ratios up to 9 dB. When compared to actual state-of-art screening techniques of chronic myeloid leukemia, these results were, at microscale, at least 10 times faster than the reported detection methods for chronic myeloid leukemia. Concerning point-of-care applications, this work paves the way for other new and more complex versions of optical based genosensors