Manipulating enhanced photoluminescence of upconversion nanoparticles by plasmonic nanostructures and broadband light absorption

Rare-earth upconversion nanoparticles, such as those composed of lanthanide-doped NaYF4, can convert two or more low-energy photons at longer wavelength into one high-energy photon at a shorter wavelength. Solar water splitting devices that incorporate them can therefore harvest otherwise lost photons in the near-infrared region of the electromagnetic spectrum. The conversion e ciencies of these nanoparticles have, however, been extremely poor to date, eliminating any potential bene t (with respect to the photocurrent of water splitting devices themselves) of being incorporated into photoelectrode devices. Towards overcoming this impasse, the aim of this Ph.D project is to investigate the feasibility of a hybrid photoelectrode system where upconverting nanoparticles are coupled to a plasmonic structure and conjugated with dye molecules that absorb below bandgap photons. The synergistic enhancement e ect of plasmonic and broadband absorption of dye molecules could signi cantly improve the conversion e ciency of lanthanide-doped NaYF4. The dye molecules act as a sensitiser: they absorb near-infrared light over a broad range and subsequently transfer the associated energy to the their upconverting nanoparticles via F orster resonance energy transfer. On the other hand, the plasmonic components enhance both the upconversion process and F orster resonance energy transfer process, by increasing the incident electromagnetic eld intensity and the radiative emission rate via surface plasmon resonance. In this project, hexagonal phase NaYF4 co-doped with Yb3+ and Er3+ upconversion nanocrystals (UCNPs) were synthesized. Plasmonic enhanced upconversion; dye-sensitised upconversion, and nally plasmonic broadband dye-sensitised upconversion were investigated using Au nanodisk (AuND) 2D arrays. The enhanced upconversion were observed with 26-fold and 19-fold enhancements for green and red emission on AuND arrays, respectively. In parallel, single infrared dye IR808 and multiple infrared dyes were conjugated to UCNPs, with 5.5-fold and 3.9-fold enhancements observed in green emission. Finally, plasmonic enhanced broadband upconversion with 10-fold enhancement was recorded. For proof of concept, UCNPs and three-dye-sensitised UCNPs coupled with AuND arrays were deposited on hematite-based photoelectrodes. Photocurrent was clearly obtained from UCNPs coupled hematite on AuND arrays when excited below the bandgap of hematite. The proof of concept established in this thesis could not only nd applications in arti cial solar water splitting, but also has huge potential in applications such as biological sensing, imaging and therapy based on upconversion nanoparticles.Open Acces

Nanoplasmonic NO2Sensor with a Sub-10 Parts per Billion Limit of Detection in Urban Air

Urban air pollution is a critical health problem in cities all around the world. Therefore, spatially highly resolved real-time monitoring of airborne pollutants, in general, and of nitrogen dioxide, NO2, in particular, is of utmost importance. However, highly accurate but fixed and bulky measurement stations or satellites are used for this purpose to date. This defines a need for miniaturized NO2 sensor solutions with detection limits in the low parts per billion range to finally enable indicative air quality monitoring at low cost that facilitates detection of highly local emission peaks and enables the implementation of direct local actions like traffic control, to immediately reduce local emissions. To address this challenge, we present a nanoplasmonic NO2 sensor based on arrays of Au nanoparticles coated with a thin layer of polycrystalline WO3, which displays a spectral redshift in the localized surface plasmon resonance in response to NO2. Sensor performance is characterized under (i) idealized laboratory conditions, (ii) conditions simulating humid urban air, and (iii) an outdoor field test in a miniaturized device benchmarked against a commercial NO2 sensor approved according to European and American standards. The limit of detection of the plasmonic solution is below 10 ppb in all conditions. The observed plasmonic response is attributed to a combination of charge transfer between the WO3 layer and the plasmonic Au nanoparticles, WO3 layer volume expansion, and changes in WO3 permittivity. The obtained results highlight the viability of nanoplasmonic gas sensors, in general, and their potential for practical application in indicative urban air monitoring, in particular

Studies of Molecular Interactions with Single Nanoparticles: Combining in Situ Plasmonic Nanospectroscopy with Transmission Electron Microscopy

The cyclic methanol and hydrogen economies are two viable options in the strive for clean energy production. Industrial methanol synthesis is conducted over copper (Cu)-based catalysts. However, Cu is prone to oxidation, which leads to Cu catalyst deactivation. This highlights the need to probe catalyst performance and deactivation during relevant conditions, and why methods for operando catalyst monitoring are sought after. Moreover, individual catalyst particle-specific characteristics, such as grain boundaries, are likely to affect deactivation. Secondly, in view of the expanding hydrogen economy, efficient and reliable hydrogen sensors are required. To this end, the slowing response rate of palladium (Pd)-based hydrogen sensors over extended hydrogen sorption cycling is problematic. To enable studies of single particle-specific performance deterioration routes, I have in this thesis developed a correlative plasmonic nanospectroscopy and transmission electron microscopy approach for in situ studies of interactions between individual nanoparticles and molecules in the gas phase. As my main focus, I have applied the method to shed light on Cu nanoparticle oxidation, both in pure O2 and under CO oxidation reaction conditions. As a main result, I identified a distinct dependence of Cu oxidation on single particle-specific structural characteristics, such as grain boundaries. Furthermore, with in situ TEM imaging temperature-dependent competing oxidation mechanisms were observed and their corresponding single particle plasmonic signatures were mapped by electron energy-loss spectroscopy.As a second example, in hydrogen sorption cycling of polycrystalline Pd nanoparticles grain-growth was observed that slowed down sorption kinetics, whereby an explanation for the deterioration of Pd-based hydrogen sensors was identified

So2 Detection Using Plasmon Damping

The distinct optical properties of noble metal nanoparticles that stem from localized surface plasmon resonance (LSPR) have fascinated scientists for centuries. In recent years, frequency-shift LSPR sensors have been receiving intense attention for chemical/biological sensing. In this work, an SO2 nanosensor based on a unique sensing mechanism, called hybrid plasmon damping, is developed. The active component of the sensor is a self-assembled monolayer of silver nanoparticles immobilized on a Si film. Nanoparticle synthesis is simple and low-cost, involving immersion of a Si thin film in a AgNO3 solution. In addition, the sensor response is monitored in real-time by a hand-held UV-vis spectrometer. The optical extinction spectrum of the nanoparticles reports increase in the LSPR bandwidth that is primarily due to chemical interface damping, caused by adsorption of SO2. This adsorbate-induced increase in damping (ΔГ) is demonstrated to be linearly proportional to the number of SO2 molecules attached to the nanoparticle surface. Therefore, the increase in damping (i.e., LSPR bandwidth) is exploited to quantify the SO2 concentration. The sensor detects 1 ppm SO2 in less than a second and at an accuracy of 94.3 %. The present work also elucidates the chemisorption configurations of SO2 to the Ag nanoparticles by surface-enhanced Raman spectroscopy.School of Materials Science & Engineerin

Portable EIS and SERS sensing with flexible sensors

To debottleneck the core development of portable sensing, in this dissertation low-cost, highly sensitive sensors for impedance sensing and surface-enhanced Raman sensing have been designed and tested with mass-manufacturing ability. Starting from silicon-based through-hole impedance with a pre-concentrating function, 100 cells per milliliter detection limit has been achieved. In the following dissertation, the difficult-to-fabricate silicon sensor was replaced by a filter-based sensor, combining with a 3D printed scaffold and low-melting 3D printed filament confining the microfluidic channel, not only the cost was reduced significantly, but the detection limit was further improved by 20 times in the study using the Hook effect and improvement of the equivalent circuit model for paper-based impedance sensing. Further, we developed a Bluetooth-based impedance sensing component that can be used with a smartphone to work with this sensor easily. On the other hand, we have developed a wafer scale, flexible, polymer-based nano-pillar SERS sensor with an enhancement factor (EF) as high as 4.81 × 108 for the silver-based sensor. This high EF resulted from better adhesion between the substrate and detecting target, as well as the extended hotspots from the dense silver nanoparticles along the nano-pillars. Furthermore, in the following work, we also increased the EF by 3.4 times for a gold-coated sensor which is more stable, and bio-compatible by fine-tuning the distance among nano-pillars. With this ultrasensitive, low-cost, and highly uniformed substrate, the application with a handheld Raman spectrometer for the detection of drugs in wine was also demonstrated

DEVELOPMENT OF ANALYTICAL METHODS FOR CHARACTERIZATION OF NANOPARTICLES FOR BIO-MEDICAL AND ENVIRONMENTAL APPLICATION BY ION MOBILITY-ICP-MS

The development of nanotechnology necessitates appropriate tools for nanoparticle characterization to assure product quality, evaluate safety and facilitate manufacturing. The properties of interest particularly relevant to nanomedicine and environmental ecotoxicology include size, shape, aggregation, concentration, dissolution, surface chemistry, and composition etc. Engineered nanoparticles in a complex matrix, at realistic concentration are two of the major challenges for analytical scientist. Potential transformation of pristine engineered nanomaterials when put in contact with either biological or environmental media further complicate the analytical task. In this dissertation, I aim to optimize and extend the application of novel hyphenated instruments consisting of differential mobility analysis (DMA) and inductively coupled plasma-mass spectrometry (ICP-MS) for real time size classification and elemental detection in biomedical and environmental fields. I have applied DMA-ICP-MS in quantitatively characterizing anti-tumor drug delivery platform to assist design and performance evaluation. Optimal balance among drug loading, stability and release performance was achieved and evaluated by DMA-ICP-MS. I have further developed a novel analytical methodology including DMA and ICP-MS operating in single particle mode (i.e. spICP-MS). I successfully demonstrated and validated the method for accurate and simultaneous size, mass and concentration measurement by NIST reference materials. DMA-spICP-MS was shown with the capability to characterize nanoparticle aggregation state and surface coating. In addition, this technique was shown to be useful for real-world samples with high ionic background due to its ability to remove dissolved ions yielding a cleaner background. Given this validated DMA-spICP-MS method, I applied it to quantifying the geometries of seven gold nanorod samples with different geometries. It was demonstrated that DMA-spICP-MS can achieve fast quantification of both length and diameter with accuracy comparable with TEM analysis. This method provided the capability to separate nanorods from spheres quantifying the geometry for each population. Finally, an interesting open and high-order rosette protein structure was investigated by electrospray-DMA. The staining procedure was optimized and effect of electrospray process on protein particle structure was evaluated. Protein particle after electrospray was largely maintained. Mobility simulation by MOBCAL showed close matches with experimental data and enabled peak assignment to various particle assembly structures

Photodetectors based on graphene pn-junctions for mid-infrared and terahertz range

Long wavelength light contains the infrared and terahertz (THz) spetral range of the spectrum. This wavelength range spans approximately from 1 µm to 1 mm. Several applications can be explored in this spectral range such as thermal imaging, temperature monitoring, night vision, etc. Moreover, molecular vibrations resonate at these energies that are the fingerprints for compounds identification via molecular spectroscopy. Also, THz light has an important role in security since at these frequencies is possible to achieve a higher resolution for imaging compared to millimeter waves that are typically used in airports. Despite all these potential applications, long wavelength light technology still remains non-fully exploited. One of the reasons is due to the lack of competing instrumentation such as sources, modulators, detectors, sensors, etc. In particular, regarding the detectors, the commercially available technology present some issues such as working at room temperature, speed, sensitivity, dynamic range, broadband frequency operation, CMOS compatibility, size and compactness, etc. The extensive research during the last years on graphene and other 2D materials has opened new possibilities of novel light matter interactions that can unveil the next generation photodectectors and sensors, ascribed to the advantages respect to conventional semiconductors. In this thesis, we focus on developing novel photodetection platforms in the mid, longwave infrared and THz range based on graphene pn-junctions with integrated metallic nanostructures and hyperbolic 2D material. We have successfully integrated an antenna with a graphene pn-junction for highly sensitive and fast THz detection in this regime. This novel terahertz detector exploits efficiently the photothermoelectric (PTE) effect, based on a design that employs a dual-gated, dipolar antenna with a nanogap. We have demonstrated that this novel detector leads to an excellent performance, which fulfills a combination of figure-of-merits that is currently missing in the state-of-the-art detectors. We also overcame the main challenge of infrared photodetectors, which is to funnel the light into a small nanoscale active area and efficiently convert it into an electrical signal. We achieve this by efficient coupling of a plasmonic antenna to hyperbolic phonon-polaritons in hBN to highly concentrate mid-infrared light into a graphene pn-junction. We use a metallic bowtie antenna and H-shape resonant gates that besides concentrating the light into its nanogap, their plasmonic resonances spectrally overlap within the upper reststrahlen band (RB) of hBN (6-7 µm), thus launching efficiently these HPPs and guiding them with constructive interferences towards the photodetector active area. Additionally, by having two different antennas orientation, it allows us to have sensitive detection in two incident polarizations. Furthermore, we have shown mid and long-wave infrared photocurrent spectroscopy via electrical detection of graphene plasmons, hyperbolic phonon-polaritons and their hybridized modes. We combined in one single platform the efficiently excited polaritonic material that also acts as a detector itself. We identified peaks in the photocurrent spectra that evolves and blue shift by increasing the gate voltage, which are related to the polaritonic resonances. Finally, we investigated the electrical detection of molecular vibrations coupled to hyperbolic phonon polaritons in hBN. We detected this strong light-matter interaction via a graphene pn-junction placed at the vicinity of the molecules-hBN stack. The edges of the gap of the local gates launch efficiently the hBN HPPs that interact with the CBP molecular resonances that are spectrally located at the upper RB. We explored this interaction as a function of the thickness of the molecular layers, near and far field contribution, etc.La luz de longitudes de onda largas consiste en el rango de infrarojo y terahercio (THz) del espectro. Este rango de longitud de ondas oscila entre los valores de 1 µm a 1 mm. En esta frecuencias, muchas aplicaciones pueden ser exploradas como por ejemplo las cámaras térmicas, monitorización de temperatura, visión nocturna, etc. Además, las vibraciones moleculares de muchos materiales oscilan en este rango de energías. Estas resonancias son utilizadas como huellas dactilares para la identificación de compuestos utilizando la espectroscopía molecular. También, la luz de terahercio juega un papel importante en el sector de seguridad. Esto se debe a que en estas frecuencias se puede conseguir una mayor resolución de imagen en comparación a las ondas milimétricas que son utilizadas mayoritariamente en los aeropuertos. A pesar de todo este potencial para diferentes sectores, la tecnología basada en luz de longitudes de onda largas sigue sin ser explotada del todo. Una de las razones es por la falta de equipos eficaces como por ejemplo las fuentes de luz, moduladores, detectores, sensores, etc. En particular, los detectores que se comercializan actualmente presentan limitaciones significativas como la temperatura de operación,velocidad, sensitividad, rango dinámico, ancho de banda de frecuencias, compatibilidad con CMOS, tamaño, etc. La investigación exhaustiva durante los últimos años en grafeno y otro materiales bidimensionales (2D) ha abierto nuevas posibilidades de nuevas interacciones entre materia y luz que podría contribuir para la nueva generación de fotodetectores y sensores debido a las ventajas de estos materiales respecto a los semiconductores convencionales. En esta tesis nos enfocaremos en el desarrollo de plataformas novedosos en fotodección en el infrarrojo medio, largo y en el rango de terahercio. Estas plataformas están basadas en junciones pn de grafeno integradas con nanoestructuras metálicas y materiales 2D hiperbólicos. Hemos integrado satisfactoriamente una antena con una junción pn de grafeno para una detección sensitividad alta y rápida de terahercio. Este fotodetector novedoso de terahercio utiliza eficientemente el efecto fototermoeléctrico, el cual esta basado en un diseño que emplea una antena con un nanogap que a su vez actúa como doble puerta. También hemos demostrado que este novedoso detector realiza un gran desempeño, consiguiendo una combinación de aspectos a destacar que actualmente no se encuentran en los detectores en literatura. Además. superamos el mayor desafío de los detectores de infrarrojo, el cual consiste en dirigir este tipo de luz en la nanoescala hacia el área activa del detector y convertirla en una señal eléctrica. Conseguimos esto mediante una acoplación eficiente de una antena plasmónica con los fonones polaritones hiperbólicos (HPPs) para concentrar altamente la luz infrarroja media a una junción pn de grafeno. Utilizamos una antenna "bowtie" metálica y unas puertas resonantes con forma de H que además de concentrar la luz en su nanogap, sus resonancias plasmónicas solapan espectralmente con la banda reststrahlen (RB) superior del hBN (6-7 µm). Esto induce a que se puedan excitar eficientemente los HPPs y se guian hacia la área activa del fotodetector mediante intereferencias constructivas. Más aún, hemos demostrado en la espectroscopía de fotocorriente en el infrarrojo medio y largo mediante la deteción eléctrica de polaritones 2D. Hemos combinado en una sola plataforma el material plasmónico que a su vez actúa como el fotodetector. Hemos identificado picos en el espectro de fotocorriente que evoluciona a medida que aumentamos el potencial de puerta, lo cual es una insignia de una resonancia polaritónica. Finalmente, investigamos la deteción eléctrica de vibraciones moleculares acopladas a HPPs en hBN. Hemos detectado esta fuerte interacción de luz y materia mediante una junción pn de grafeno que esta próxima a estePostprint (published version