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Organic–inorganic layered perovskites are currently some of the most promising 2D van der Waals materials. Low crystal quality usually broadens the exciton line width, obscuring the fine structure of the exciton in conventional photoluminescence experiments. Here, we propose a mechanical approach to reducing the effect of spectral diffusion by means of hBN capping on layered perovskites, revealing the exciton fine structure. We used a stochastic model to link the reduction of the spectral line width with the population of charge fluctuation centers present in the organic spacer. van der Waals forces between both lattices cause the partial clamping of the perovskite organic spacer molecules, and hence the amplitude of the overall spectral diffusion effect is reduced. Our work provides a low-cost solution to the problem of accessing important fine-structure excitonic state information, along with an explanation of the important carrier dynamics present in the organic spacer that affect the quality of the optical emission.

Chemical sensors based on fluorescent quantum dots have attracted intense interest because of their excellent optical and electronic properties compared to the routinely employed fluorescent organic dyes. This study reports a CdSe QD-polymer-based luminescent chemosensor, which is based on an array containing either green-emitting or red-emitting CdSe QDs embedded in polycaprolactone as a polymer host matrix. We evaluate the sensing capability of the nanocomposites by exposing both sensors to vapors of explosive taggants, explosive-like molecules, and some common solvents. Both nanocomposites exhibit a very fast response time of

Solid-state luminescent gas sensor based on CsPbBr3 NCs embedded in a molecularly imprinted polymer (MIP) with fast response and high selectivity to nitro compounds.

An unusual spectrally reproducible near-IR random lasing (RL) with no fluctuation of lasing peak wavelength is disclosed in polycrystalline films of formamidinium tin triiodide perovskite, which have been chemically stabilized against Sn

An outstanding potentiality of layered two-dimensional (2D) organic–inorganic hybrid perovskites (2DHPs) is in the development of solar cells, photodetectors, and light-emitting diodes. In 2DHPs, an exciton is localized in an atomically thin lead(II) halide inorganic layer of sub-nanometer thickness as in a quantum well sandwiched between organic layers as energetic and dielectric barriers. In previous years, versatile optical characterization of 2DHPs has been carried out mainly for thin flakes of single crystals and ultrathin (of the order of 20 nm) polycrystalline films, whereas there is a lack of optical characterization of thick (hundreds of nanometers) polycrystalline films, fundamentals for fabrication of devices. Here, with the use of photoluminescence (PL) and absorption spectroscopies, we studied the exciton behavior in ∼200 nm polycrystalline thin films of 2D perovskite (PEA)2PbI4, where PEA is phenethylammonium. Contrary to the case of ultrathin films, we have found that peak energies and line width of the excitonic bands in our films demonstrate unusual extremely weak sensitivity to temperature in 20–300 K diapason. The excitonic PL band is characterized by a significant (∼30 meV) Stokes shift with respect to the corresponding absorption band as well as by a full absence of the exciton fine structure at cryogenic temperatures. We suggest that the observed effects are due to the large inhomogeneous broadening of the excitonic PL and absorption bands resulting from the (PEA)2PbI4 band gap energy dependence on the number of lead(II) halide layers of individual crystallites. The characteristic time of the exciton energy funneling from higher- to lower-energy crystallites within (PEA)2PbI4 polycrystalline thin films is about 100 ps.

Bandgap engineering and quantum confinement in semiconductor heterostructures provide the means to fine-tune material response to electromagnetic fields and light in a wide range of the spectrum. Nonetheless, forming semiconductor heterostructures on lattice-mismatched substrates has been a challenge for several decades, leading to restrictions for device integration and the lack of efficient devices in important wavelength bands. Here, we show that the van der Waals epitaxy of two-dimensional (2D) GaSe and InSe heterostructures occur on substrates with substantially different lattice parameters, namely silicon and sapphire. The GaSe/InSe heterostructures were applied in the growth of quantum wells and superlattices presenting photoluminescence and absorption related to interband transitions. Moreover, we demonstrate a self-powered photodetector based on this heterostructure on Si that works in the visible-NIR wavelength range. Fabricated at wafer-scale, these results pave the way for an easy integration of optoelectronics based on these layered 2D materials in current Si technology., 16 Pages, 5 figures. Supplementary Information included in the end (+10 pages, +10 Figures, + 2 Tables). Partially presented at 21st ICMBE - September 2021

Sensor elements based on localized surface plasmon resonance phenomenon in arrays of Au nanostructures on glass substrates (nanochips) with molecularly imprinted acrylamide copolymer coating have been proposed for explosives analogues sensing in liquid and vapor phase. Nanochips exhibited detection limits of 1 pM in aqueous solution and 0.1 ppm in gaseous state against 4-nitrophenol. Vapor phase sensing of 4-nitrotoluene, 1-nitronaphthalene and 5-nitroisoquinoline using the developed 4-nitrophenol-imprinted plasmonic nanochips demonstrated partially selective response with time to signal saturation starting from 2 minutes.

We have designed a synthesis procedure to obtain Cs

We have designed a synthesis procedure to obtain Cs2SnCl6 nanocrystals (NCs) doped with metal ion(s) to emit visible light. Cs2SnCl6 NCs doped with Bi3+, Te4+ and Sb3+ ions emitted blue, yellow and red light, respectively. In addition, NCs simultaneously doped with Bi3+ and Te4+ ions were synthesized in a single run. Combination of both dopant ions together gives rise to the white emission. The photoluminescence quantum yields of the blue, yellow and white emissions are up to 26.5, 28, and 16.6%, respectively under excitation at 350, 390, and 370 nm. Pure white-light emission with CIE chromaticity coordinates of (0.32, 0.33) and (0.32, 0.32) at 340 and 370 nm excitation wavelength, respectively, was obtained. The as-prepared NCs were found to demonstrate a long-time stability, resistance to humidity, and an ability to be well-dispersed in polar solvents without property degradation due to their hydrophilicity, which could be of significant interest for wide application purposes.

A FASnI3 lead-free perovskite is integrated in a flexible waveguide to demonstrate Amplified Spontaneous Emission. An extremely low threshold, 1 µJ/cm2, is observed together with the formation of narrow random lasing lines (< 1 nm).

Lead halide perovskites (LHPs) have arisen as a new class of semiconductors with excellent perspectives to become an alternative to traditional III–V epitaxial nanostructures for applications in active photonics. From the earliest demonstration of amplified spontaneous emission (ASE) with CH3NH3PbX3 (X = Cl, Br, I) polycrystalline thin films in 2014, more than 200 papers have been published in this field with regards to the improvement of the ASE figures of merit or the understanding of the underlaying physical mechanisms in the generation of optical gain for different LHPs. This extraordinary progress has resulted in the synthesis of either CH3NH3PbX3 perovskites as polycrystalline thin films or layers made of fully inorganic CsPbX3 perovskite nanocrystals (PNCs) that can be integrated in different optical architectures or substrates using cheap and straightforward solution processing techniques. Consequently, ASE with thresholds smaller than a few nJ cm−2 or lasing under continuous wave operation, among other impressive results, have been recently achieved. The role of the radiative recombination time, nonradiative traps, Auger recombination, excitation fluency, and absorption coefficient are discussed in this chapter within the framework of available studies and results in the literature, as well as in the light of our own work. This chapter will also review the most important results obtained by the scientific community in the field of active photonic devices and integrated concepts based on LHPs, which contain the integration of bulk polycrystalline and PNC thin films on different substrates, even those which are flexible. Spontaneous emission and ASE will be discussed based on a rate equation model incorporated into a beam propagation algorithm, in the case of optical waveguides, to simulate the generation and propagation of emitted light and optical gain, as an important tool toward the design of active integrated photonics based on LHPs.

Metal halides with perovskite crystalline structure have given rise to efficient optoelectronic and photonic devices. In the present work, we have studied the light emission properties of single CsPbBr3 and CsPbI3 semiconductor perovskite nanocrystals (PNCs), as the basis for a statistical analysis of micro-photoluminescence (micro-PL) spectra measured on tens of them. At room temperature, the linewidth extracted from PL spectra acquired in dense films of these nanocrystals is not very different from that of micro-PL measured in single nanocrystals. This means that the homogeneous linewidth due to exciton-phonon interaction is comparable or larger than the inhomogeneous effect associated to the micro-PL peak energy dispersion due to the nanocrystal size distribution defined by the chemical synthesis of the PNCs. Contrarily, we observe very narrow micro-PL lines in CsPbBr3 and CsPbI3 PNCs at 4 K, in the range of 1–5 meV and 0.1–0.5 meV, respectively, because they are limited by spectral diffusion. Aging of PNCs under ambient conditions has been also studied by micro-PL and a clear reduction of their nanocube edge size in the order of the nm/day is deduced.

The poor photostability under ambient conditions of hybrid halide perovskites has hindered their recently explored promising nonlinear optical properties. Here, we show how Bi3+ can partially substitute Pb2+ homogeneously in the commonly studied MAPbI3, improving both environmental stability and photostability under high laser irradiation. Bi content around 2 atom % produces thin films where the nonlinear refractive (n2) and absorptive coefficients (β), which modify the refractive index (Δn) of the material with light fluence (I), increase up to factors of 4 and 3.5, respectively, compared to undoped MAPbI3. Higher doping inhibits the nonlinear parameters; however, the samples show higher fluence damage thresholds. Thus, these results provide a road map on how MAPbI3 can be engineered for practical cost-effective nonlinear applications by means of Bi doping, including optical limiting devices and multiple-harmonic generation into optoelectronics devices.

Metal halide perovskites in the form of nanocrystals are highly efficient light emitters at visible-NIR wavelengths. In this work, the optical properties of single nanocrystals and ensembles will be discussed, as also several applications in nanophotonics. At low temperatures, single nanocrystals can be also single photon emitters if blinking and spectral diffusion is conveniently reduced. In the case of nanocrystal assemblies, stimulated emission can be observed with thresholds lower than 10 μJ/cm2 under nanosecond laser excitation at low temperatures, whose physical origin is attributed to single exciton recombination. Finally, the coupling of perovskite nanocrystals to the optical modes of hyperbolic metaldielectric metamaterials has been studied and demonstrated an important Purcell enhancement of the exciton radiative emission by more than a factor three for CsPbI3 and around factor two for FAPbI3 when the distance between the emitters and HMM is 10 nm.

During the last years, organometallic lead halide perovskites (LHP) have been widely studied as outstanding materials for photovoltaics and photonics applications [1] . These emerging semiconductors are fabricated by cheap and straightforward solution process techniques on polycrystalline film of the compound CH 3 NH 3 PbX 3 (X=Cl, Br, I). Their outstanding properties of these films include large absorption coefficients above the bandgap, high electronic mobilities, high quantum yield of emission at room temperature or tunable band-gap with the composition [1] . In this work, we exploit the excellent light emitting and photodetection properties of CH 3 NH 3 PbI 3 thin films to integrate a waveguide amplifier and a photodetector within the same LHP thin film deposited in both rigid (SiO 2 /Si) and flexible (nanocellulose) substrates. As illustrated in Figure 1a , the device is based on the refractive index contrast between the LHP, a poly(methyl methacrylate) capping layer the substrate to engineer the number of propagating modes and their propagation constant [1] . In particular, the geometrical parameters of the structure were carefully designed to propagate an excitation beam injected at the input edge of the structure together with the photoluminescence (PL) emitted by the LHP through a mode that is extremely confined in the semiconductor film (see Fig. 1a ). As a result, this bilayer structure demonstrates amplified the spontaneous emission (ASE) with extraordinary low thresholds (2 nJ) [2] . Moreover, the incorporation of electrodes on the top of the LHP allows us to study a photocurrent dependent on the excitation light ( Fig. 1b ), and with it to monitor electrically the generation of PL and ASE ( Fig. 1c ). Experimental results (symbols in Fig. 3c) are properly reproduced with the simulations carried out with a rate equation model (solid lines in Fig. 3c). Here, we carefully compare the generation of optical gain and photocurrent in rigid and flexible substrates and demonstrate that the choice flexible substrate does not significantly alter the performances of the device [3] . Therefore, this approach illustrates a new amplifier-photodetector device that can pave the road towards a flexible and wearable technology LHP based technology.

The manipulation of light emitted by two-dimensional semiconductors grounds forthcoming technologies in the field of on-chip communications. However, these technologies require from the so elusive out-of-plane photon sources to achieve an efficient coupling of radiated light into planar devices. Here we propose a versatile spectroscopic method that enables the identification of the out-of-plane component of dipoles. The method is based on the selective coupling of light emitted by in-plane and out-of-plane dipoles to the whispering gallery modes of spherical dielectric microresonators, in close contact to them. We have applied this method to demonstrate the existence of dipoles with an out-of-plane orientation in monolayer WSe2 at room temperature. Micro-photoluminescent measurements, numerical simulations based on finite element methods, and ab-initio calculations have identified trions as the source responsible for this out-of-plane emission, opening new routes for realizing on-chip integrated systems with applications in information processing and quantum communications. Out-of-plane photon emission in 2D semiconductors is rare but crucial for efficient light manipulation in planar optoelectronic devices and photonic chips. Here, an out-of-plane dipolar component of trions in monolayer WSe2 is revealed by exciting the whispering gallery modes of SiO2 microspherical resonators.

An ongoing demand toward lead-free all-inorganic cesium metal halide perovskites has presented Sn(II) as an ideal substitute of Pb(II) for applications in optoelectronic devices. The major concern regarding Sn(II) is the instability due to the ambient oxidation to Sn(IV). To expand the scope of traditional perovskite and analogues, herein the synthesis and optical performance of Sn(II)-doped CsBr, a new material formed by interstitial doping of Sn(II) into the CsBr matrix, are reported for the first time. This material is prepared following an antisolvent mediated recrystallization method using a continuous flow reactor, which is beneficial for scaling up the production compared to traditional batch reactors. Sn(II)-doped CsBr exhibits broadband orange emission with full-width-half-maximum of 180 nm and a photoluminescence quantum yield of 21.5%. The emission turned to be highly stable over 7 months despite containing Sn(II). It is suggested that this is due to interstitial location of Sn(II) atoms in bulk of microcrystals. A broadband emission and high aerobic stability are attractive properties of the material for white-light emitting applications. Funding for open access charge: CRUE-Universitat Jaume I

Solution processed all-inorganic trihalide perovskite nanocrystals are potential materials for the fabrication of future generation optoelectronic devices. However, the surface of the perovskite nanocrystals should be encapsulated to prevent degradation. Because of their stability under ambient conditions, nanocomposites of perovskite nanocrystals have been intensively researched for display applications. Perovskite nanocrystals dispersion or growth in a polymer matrix imparts structural stability and influences the optical properties, preventing effects such as halide migration. Developing flexible, high-performance lighting devices through perovskite nanocomposites will need to be evaluated on the compatibility of nanocrystals within the polymer matrix. Research in this area has escalated, but specific attention is required to address the practical challenges. This chapter discusses the current developments in the field of preparation and processing of nanocomposites of pure inorganic perovskite nanocrystals. Organic ligands, fabrication methods, encapsulating compounds, solvents, and other deposition procedures affecting the performance and stability of nanocomposites are discussed.

Hexagonal boron nitride (hBN) is a wide-band gap van der Waals material able to host light-emitting centers behaving as single photon sources. Here, we report the generation of color defects in hBN nanosheets dispersed on different kinds of substrates by thermal treatment processes. The optical properties of these defects have been studied using microspectroscopy techniques and far-field simulations of their light emission. Using these techniques, we have found that subsequent ozone treatments of the deposited hBN nanosheets improve the optical emission properties of created defects, as revealed by their zero-phonon linewidth narrowing and reduction of background emission. Microlocalized color defects deposited on dielectric substrates show bright (approximate to 1 MHz) and stable room-temperature light emission with zero-phonon line peak energy varying from 1.56 to 2.27 eV, being the most probable value 2.16 eV. In addition to this, we have observed a substrate dependence of the optical performance of the generated color defects. The energy range of the emitters prepared on gold substrates is strongly reduced, as compared to that observed in dielectric substrates or even alumina. We attribute this effect to the quenching of low-energy color defects (these of energies lower than 1.9 eV) when gold substrates are used, which reveals the surface nature of the defects created in hBN nanosheets. Results described here are important for future quantum light experiments and their integration in photonic chips. Horizon 2020 research and innovation program through the S2QUIP [8204023]; Spanish MINECO [TEC2017-86102-C2-1-R]; S2QUIP project [CPI-18-404, CPI-18-418]; Generalitat Valenciana European Commission; NanoSense through the Flemish Scientific Foundation (FWO)FWOGeneral Electric; Spanish Ministry of Science MICINN AEI [RTI2018-099015-J-I00]; FWOFWO [G0E7417N, G0A0520N]; Quantum Flagship project ASTERIQS [820394]; QuantERA project Q