We present the novel design of photosystem I (PSI)-based biosolar cell, whereby conductive transparent electrode materials, such as ITO or FTO, are replaced with glass covered with silver island film. This nanostructured metallic layer combines high electric conductance with enhancing the absorption efficiency of the PSI biocatalyst via the plasmonic effect. We demonstrate strong enhancement of the photocurrent generated in the biohybrid electrode composed of oriented layers of PSI reaction centers due to plasmonic interactions of the PSI fluorophores and redox centres with the conductive silver island film.

Photon avalanche (PA) is one of energy up-conversion processes, which is characterized by highly nonlinear relation between the luminescence intensity and the excitation power. Demonstrating PA in nanocrystals paved the way to new potential applications in optoelectronics, sensorics, and imaging. We present the essential aspects of photon avalanching in the context of super-resolution imaging, including the mechanism of improved lateral resolution in raster scanning with a single Gaussian excitation beam. Moreover, we discuss the impact of the luminescence rise dynamics on the imaging based on the photon avalanche effect.

Precise deposition of materials on surfaces is one of the crucial steps in a broad range of applications and functional device fabrication at both the micro- and nanoscale. Semiconductor quantum dots (QDs), with their unique optical and physical properties, have frequently been a focus of attempts for micro- or nano-positioning. Here, we present a method for reproducible, repetitive, and precise deposition of QD-containing microdroplets using hydrophobic micropipettes without any need to apply an actuation voltage. We show that upon deposition, the droplets can be translated across the surface and placed in defined patterns. The incorporation of semiconductor QDs allows for the confirmation of the morphological integrity of the microdroplets after deposition and translation. Fluorescence blinking observed for droplets containing highly diluted QD solution proves that our approach is suitable for embedding individual emitters in such microdroplets.

Photon avalanche (PA)-where the absorption of a single photon initiates a 'chain reaction' of additional absorption and energy transfer events within a material-is a highly nonlinear optical process that results in upconverted light emission with an exceptionally steep dependence on the illumination intensity. Over 40 years following the first demonstration of photon avalanche emission in lanthanide-doped bulk crystals, PA emission has been achieved in nanometer-scale colloidal particles. The scaling of PA to nanomaterials has resulted in significant and rapid advances, such as luminescence imaging beyond the diffraction limit of light, optical thermometry and force sensing with (sub)micron spatial resolution, and all-optical data storage and processing. In this review, we discuss the fundamental principles underpinning PA and survey the studies leading to the development of nanoscale PA. Finally, we offer a perspective on how this knowledge can be used for the development of next-generation PA nanomaterials optimized for a broad range of applications, including mid-IR imaging, luminescence thermometry, (bio)sensing, optical data processing and nanophotonics.

Data processing and storage in electronic devices are typically performed as a sequence of elementary binary operations. Alternative approaches, such as neuromorphic or reservoir computing, are rapidly gaining interest where data processing is relatively slow, but can be performed in a more comprehensive way or massively in parallel, like in neuronal circuits. Here, time-domain all-optical information processing capabilities of photon-avalanching (PA) nanoparticles at room temperature are discovered. Demonstrated functionality resembles properties found in neuronal synapses, such as: paired-pulse facilitation and short-term internal memory, in situ plasticity, multiple inputs processing, and all-or-nothing threshold response. The PA-memory-like behavior shows capability of machine-learning-algorithm-free feature extraction and further recognition of 2D patterns with simple 2 input artificial neural network. Additionally, high nonlinearity of luminescence intensity in response to photoexcitation mimics and enhances spike-timing-dependent plasticity that is coherent in nature with the way a sound source is localized in animal neuronal circuits. Not only are yet unexplored fundamental properties of photon-avalanche luminescence kinetics studied, but this approach, combined with recent achievements in photonics, light confinement and guiding, promises all-optical data processing, control, adaptive responsivity, and storage on photonic chips.

Photon avalanche is one of the anti-Stokes upconversion processes characterized by highly nonlinear response of the emission intensity to excitation power density changes. By exceeding the critical pumping power threshold, even minute increase of this power results in a steep increase (by 2-3 orders of magnitude) of the emission intensity. While photon avalanche has been observed in bulk materials since 80-ties, it was reported in thulium-doped nanocrystals only recently, enabling to use them for single excitation beam super-resolution imaging. In current work we explore new perspectives for nanoscale avalanche phenomenon by combining the avalanching materials with plasmonically active metallic nanostructures.

Photon avalanche (PA) is a highly nonlinear luminescence phenomenon that occurs in lanthanide doped materials. PA exhibits a very steep power law relationship between luminescence intensity and the optical pump power. Due to the mechanism of PA emission, even weak perturbations to the energy looping and energy distribution within excited levels of lanthanide emitters are expected to significantly modify luminescent properties. Therefore, in this work, we experimentally study the impact of temperature (from – 175 to 175 °C, with 25 °C steps) on the sensitized PA emission in NaYF4 nanoparticles co-doped with 15% of Yb3+ and 0.5% of Pr3+ ions under 852 nm pumping wavelength. Significant variations of the PA nonlinearity (S = 4.5–9), PA gain (from 50 up to 175), and PA threshold (from 100 up to 700 kW/cm2) were observed under temperature rise from – 175 to 175 °C, respectively. The relative temperature sensitivities based on luminescence intensity changes were larger than 1.5% °C–1 in the whole temperature range, reaching the maximal value of 7.5% °C–1 at 0 °C. Moreover, a new thermometric parameter was proposed, namely, the PA pump power threshold, which exhibited over 0.5% °C–1 relative sensitivities in the same wide temperature range. Owing to PA properties, the temperature sensitivity range and the corresponding relative sensitivities may be intentionally tuned by selecting the appropriate pump intensity in respect to the power dependence relationship. These studies not only provide a better understanding of fundamental processes and susceptibility of the sensitized photon avalanche emission to temperature variation, but also show the possibility of using PA materials as sensitive (nano)thermometers.

The seven N -phthalimide derivatives substituted with the amine group at the 3-C position in the phenylene ring were synthesized. The effect of N -substituent chemical structure was investigated. The thermal, electrochemical and optical studies were performed and supported by the density functional theory calculations (DFT). The electrochemical investigations of the synthesized low-molecular phthalimides revealed the one oxidation and reduction process with the HOMO energy level under − 5.81 eV and energy-band gap below 3 eV. The N -phthalimide derivatives were emitted light in a blue spectral region in solutions (in polar and non-polar) with the quantum yield between 2 and 68%, dependent on the substituent at the nitrogen atom, solvent and concentration. The N -phthalimide derivatives were emissive also in a solid state as a thin film and powder. They were tested as a component of the active layer with PVK:PBD matrix and as an independent active layer in the organic light-emitting diodes. The registered electroluminescence spectra exhibited the maximum emission band in the 469–505 nm range, confirming the possibility of using N -phthalimides with PVK:PBD matrix as the blue emitters.

Through a wise design of materials composition and chemical architecture, modern functional nanomaterials should offer enhanced properties and multifunctional capabilities. This is why new photothermal agents are sought that not only are efficient in light-to-heat conversion but advance other functionalities such as luminescence based sensing that assure feedback control or thermal triggering / activation of (bio)chemical processes. In this work YPO4:Cr3+ nanoparticles are presented and their photothermal performance is evaluated as a function of Cr3+ ions concentration. As demonstrated, the high absorption cross-section of Cr3+ ions causes that despite the light-to-heat conversion efficiency for CrPO4 reached only 15% the temperature raises obtained with optical excitation of 4.3 kW/cm2 is 250% higher for CrPO4 compared to NaNdF4 nanoparticles. The high application potential of the presented photothermal agents was demonstrated in an experiment with dynamic photo-thermo-polymerization of MMA that can be used for 3D printing.

Among different upconversion processes where the emitted photon has higher energy than the one absorbed, photon avalanche (PA) is unique, because the luminescence intensity increases by 2-3 orders of magnitude in response to a tiny increase in excitation intensity. Since its discovery in 1979, PA has been observed in bulk materials but until recently, obtaining it at the nanoscale has been a significant challenge. In the present work, the PA phenomenon in β-NaYF4 colloidal nanocrystals co-doped with Pr3+ and Yb3+ ions was successfully observed at 482 nm (3P0 → 3H4) and 607 nm (3P0 → 3H6) under excitation at 852 nm. The impact of Pr3+ ion concentration and pump power dependence on PA behavior was investigated, i.e. PA non-linearity slopes of luminescence intensity curves as a function of pump power density as well as PA thresholds. The highest slopes, namely 8.6 and 9.0, and the smallest thresholds equal to 286 kW cm-2 and 281 kW cm-2, observed for emission bands at 607 nm and 482 nm, respectively, were obtained for NaYF4:0.5%Pr3+,15%Yb3+@NaYF4 colloidal nanocrystals. Besides experimental research, simulations of PA behavior in Pr3+, Yb3+ co-doped materials were performed based on differential rate equations describing the phenomena that contribute to the existence of PA. The influence of different processes leading to PA, e.g. the rates of nonradiative and radiative transitions as well as energy transfers, on PA performance was simulated aiming to understand their roles in this complex sensitized system.

Materials capable of emitting ultraviolet (UV) radiation are sought for applications ranging from theranostics or photodynamic therapy to specific photocatalysis. The nanometer size of these materials, as well as excitation with near-infrared (NIR) light, is essential for many applications. Tetragonal tetrafluoride LiY(Gd)F-4 nanocrystalline host for up-converting Tm3+-Yb3+ activator-sensitizer pair is a promising candidate to achieve UV-vis up-converted radiation under NIR excitation, important for numerous photo-chemical and bio-medical applications. Here, we provide insights into the structure, morphology, size and optical properties of up-converting LiYF4:25%Yb(3+)0.5%Tm3+ colloidal nanocrystals, where 1, 5, 10, 20, 30 and 40% of Y3+ ions were substituted with Gd3+ ions. Low gadolinium dopant concentrations modify the size and up-conversion luminescence, while the Gd3+ doping that is exceeding the structure resistance limit of the tetragonal LiYF4 results in appearance of foreign phase and significant decrease of luminescence intensity. The intensity and kinetic behavior of Gd3+ up-converted UV emission are also analyzed for various gadolinium ions concentrations. The obtained results form a background for further optimized materials and applications based on LiYF4 nanocrystals.

Chromium doped luminescent phosphors display numerous spectral features that can be useful for designing modern multi-functional materials.

Photon avalanche (PA) is a highly nonlinear mode of upconversion that is characterized by 100–1000‐fold increase in luminescence intensity upon minute increments of pumping power. The practical realization of numerous possible nano‐bio‐technology applications utilizing the PA phenomenon will require information on its susceptibility to the material volume and surface. Here, these parameters are investigated via experimental and theoretical PA. The two‐color, highly nonlinear PA emission at 475 and 800 nm is clearly observed in bulk single crystal, individual microcrystals, and ensembles of colloidal core and core–shell nanoparticles of LiYF 4 host doped with either 3 or 8% of thulium ions. The properties of PA emission, such as PA nonlinearity, PA gain, PA intensity, and luminescence kinetics in these materials show dependence on crystal volume and surface quenching. Theoretical simulations provide understanding of key physical processes that influence PA performance. Moreover, photon avalanche single beam super‐resolution imaging is realized for the first time in 3% Tm 3+ doped LiYF 4 core–shell nanoparticles. The obtained insights and predictions form a solid background for further development and applications of new optimized PA materials.

Fluorescence excitation spectroscopy at cryogenic temperatures carried out on hybrid assemblies composed of photosynthetic complexes deposited on a monolayer graphene revealed that the efficiency of energy transfer to graphene strongly depended on the excitation wavelength. The efficiency of this energy transfer was greatly enhanced in the blue-green spectral region. We observed clear resonance-like behavior for both a simple light-harvesting antenna containing only two chlorophyll molecules (PCP) and a large photochemically active reaction center associated with the light-harvesting antenna (PSI–LHCI), which pointed towards the general character of this effect.

Currently available temperature measurements or imaging at nano-micro scale are limited to fluorescent molecules and luminescent nanocrystals, whose spectral properties respond to temperature variation. The principle of operation of these conventional temperature probes is typically related to temperature induced multiphonon quenching or temperature dependent energy transfers, therefore, above 12%/K sensitivity and high thermal resolution remain a serious challenge. Here we demonstrate a novel class of highly sensitive thermographic phosphors operating in room temperature range with milikelvin thermal resolution, whose temperature readings are reproducible, luminescence is photostable and brightness is not compromised by thermal quenching. Corroborated with phase transition structural characterization and high spatio-temporal temperature imaging, we demonstrated that optically active europium ions are highly and smoothly susceptible to monoclinic to tetragonal phase transition in LiYO2 host, which is evidenced by changed number and the splitting of Stark components as well as by smooth variation of contribution between magnetic and electric dipole transitions. Further, reducing the size of phosphor from bulk to nanocrystalline matrix, shifted the phase transition temperature from 100oC down to room temperature. These findings provide insights into the mechanism underlaying phase transition based luminescence nanothermometry and motivate future research toward new, highly sensitive, high temporal and spatial resolution nano-thermometers aiming at precise studying heat generation or diffusion in numerous biological and technology applications.

One of the crucial challenges for science is the development of alternative pollution-free and renewable energy sources. One of the most promising inexhaustible sources of energy is solar energy, and in this field, solar fuel cells employing naturally evolved solar energy converting biocomplexes—photosynthetic reaction centers, such as photosystem I—are of growing interest due to their highly efficient photo-powered operation, resulting in the production of chemical potential, enabling synthesis of simple fuels. However, application of the biomolecules in such a context is strongly limited by the progressing photobleaching thereof during illumination. In the current work, we investigated the excitation wavelength dependence of the photosystem I photodamage dynamics. Moreover, we aimed to correlate the PSI–LHCI photostability dependence on the excitation wavelength with significant (ca. 50-fold) plasmonic enhancement of fluorescence due to the utilization of planar metallic nanostructure as a substrate. Finally, we present a rational approach for the significant improvement in the photostability of PSI in anoxic conditions. We find that photobleaching rates for 5 min long blue excitation are reduced from nearly 100% to 20% and 70% for substrates of bare glass and plasmonically active substrate, respectively. Our results pave promising ways for optimization of the biomimetic solar fuel cells due to synergy of the plasmon-induced absorption enhancement together with improved photostability of the molecular machinery of the solar-to-fuel conversion.

A new excitation scheme broadens the choice of colours for the near-infrared excitable photon avalanching nanoscale labels for super-resolution imaging.

In the current work, comprehensive photophysical and electrochemical studies were performed for eight rhenium(I) complexes incorporating 2,2':6',2″-terpyridine (terpy) and 2,6-bis(pyrazin-2-yl)pyridine (dppy) with appended 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl, and 1-pyrenyl groups. Naphthyl and phenanthrenyl substituents marginally affected the energy of the MLCT absorption and emission bands, signaling a weak electronic coupling of the appended aryl group with the Re(I) center. The triplet MLCT state in these complexes is so low lying relative to the triplet 3ILaryl that the thermal population of the triplet excited state delocalized on the organic chromophore is ineffective. The attachment of the electron-rich pyrenyl group resulted in a noticeable red shift and a significant increase in molar absorption coefficients of the lowest energy absorption of the resulting Re(I) complexes due to the contribution of intraligand charge-transfer (ILCT) transitions occurring from the pyrenyl substituent to the terpy/dppy core. At 77 K, the excited states of [ReCl(CO)3(Ln-κ2N)] with 1-pyrenyl-functionalized ligands were found to have predominant 3ILpyrene/3ILCTpyrene→terpy character. The 3IL/3ILCT nature of the lowest energy excited state of [ReCl(CO)3(4'-(1-pyrenyl)-terpy-κ2N)] was also evidenced by nanosecond transient absorption and time-resolved emission spectroscopy. Enhanced room-temperature emission lifetimes of the complexes [ReCl(CO)3(Ln-κ2N)] with 1-pyrenyl-substituted ligands are indicative of the thermal activation between 3MLCT and 3IL/3ILCT excited states. Deactivation pathways occurring upon light excitation in [ReCl(CO)3(4'-(1-naphthyl)-terpy-κ2N)] and [ReCl(CO)3(4'-(1-pyrenyl)-terpy-κ2N)] were determined by femtosecond transient absorption studies.

Photon avalanche (PA) is an anti-Stokes process in which lanthanide-doped materials can emit upconverted luminescence in a highly non-linear manner. PA was recently demonstrated in thulium (III)-doped NaYF4 colloidal nanoparticles at room temperature, with reported nonlinearities (power factors) exceeding 30. Importantly, good rate-equations model agreement with experimental data was achieved, which enabled the derivation of the rates of energy transfer processes, providing a foundation for further developments and optimization of similar materials and their new applications. In order to apply PA to, for example, luminescent (nano)thermometry, we need to have a better understanding of the susceptibility of photon avalanche phenomenon to temperature variation. For this purpose, we study how the temperature and energy-gap-dependent multiphonon relaxation and inter-ionic energy transfer processes affect the photon avalanche behavior. As a result of these simulations, high susceptibility to temperature changes with relative sensitivity over 40 %⋅K−1 above 400 K (up to 15 %⋅K−1at room temperature) was noted. Moreover, by knocking-out the temperature dependences of the individual processes involved in the PA, we found the temperature dependence of the multiphonon relaxation of the intermediate F34 state to the ground state to be the primary one responsible for the simulated temperature dependence of PA emission. This process is observed to be more significant than temperature dependencies of energy looping and phonon assisted ground state non-resonant absorption. Although there are challenges with a single band technique, these results still show the great potential, especially when used ratiometrically with different excitation wavelengths.

Four new 1-phenyl-1H-phenanthro[9,10-d]imidazole derivatives containing N-donor substituents at the C2 position were synthesized using simple condensation reaction. Thermal, electrochemical, spectroelectrochemical, and optical properties of synthesized compounds were investigated, while their purity was confirmed by NMR spectroscopy and HRMS. They are characterized by high thermal stability above 243 degrees C. Electrochemical measurements were carried out in dichloromethane (DCM) and THF. Quasi-reversible peaks of N2 and N5 oxidation as opposed to irreversible oxidation in THF were observed in DCM. N2 - N5 exhibit at least three well-developed absorption bands, which is typical for pi ->pi* transitions. All phenanthro[9,10-d]imidazole derivatives exhibit high photoluminescence quantum yields in the range of 34%-82% in solution. Additionally, the electroluminescent ability of the synthesized compounds was preliminarily tested.