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Antimony-based 0-dimensional metal halides (0D-MHs) are attracting attention owing to their bright Stokes-shifted luminescence due to self-trapped excitons (STEs). One unexplored motif to expand their functionalities is to dope them with optically and/or magnetically active dopants that participate in energy-transfer schemes involving STEs. We investigated the photophysical and magnetic properties of Rb7Sb3Cl16nanocrystals doped with Mn2+ions, which introduce strong magnetism and activate their characteristic intra-d luminescence. By controlling the doping level, we optimize the STE → Mn2+energy transfer and tune the magnetic character of the NCs. Particles lightly doped with isolated Mn2+centers exhibit paramagnetic character and temperature-independent luminescence. By contrast, highly doped NCs show a clear transition to antiferromagnetic behavior at cryogenic temperatures similar to the behavior of low-dimensional manganese halides, accompanied by enhanced Mn emission due to suppressed exciton migration among the dopant subnetwork, thus pointing to an intimate link between the optical and magnetic properties also in Sb-based 0D-MHs.

We employed oleylphosphonic acid (OLPA) for the synthesis of CsPbBr3 nanocrystals (NCs). Compared to phosphonic acids with linear alkyl chains, OLPA features a higher solubility in apolar solvents, allowing us to work at lower synthesis temperatures (100 °C), which in turn offer a good control over the NCs size. This can be reduced down to 5.0 nm, giving access to the strong quantum confinement regime. OLPA-based NCs form stable colloidal solutions at very low concentrations (∼1 nM), even when exposed to air. Such stability stems from the high solubility of OLPA in apolar solvents, which enables these molecules to reversibly bind/unbind to/from the NCs, preventing the NCs aggregation/precipitation. Small NCs feature efficient, blue-shifted emission and an ultraslow emission kinetics at cryogenic temperature, in striking difference to the fast decay of larger particles, suggesting that size-related exciton structure and/or trapping-detrapping dynamics determine the thermal equilibrium between coexisting radiative processes.

In this work, we report the hot-injection synthesis of Cs3ZnCl5 colloidal nanocrystals (NCs) with tunable amounts of Cu+ and Mn2+ substituent cations. All the samples had a rodlike morphology, with a diameter of 14 nm and a length of 30-100 nm. Alloying did not alter the crystal structure of the host Cs3ZnCl5 NCs, and Cu ions were mainly introduced in the oxidation state +1 according to X-ray photoelectron and electron paramagnetic resonance spectroscopies. The spectroscopic analysis of unalloyed, Cu-alloyed, Mn-alloyed, and Cu, Mn coalloyed NCs indicated that (i) the Cs3ZnCl5 NCs have a large band gap of 5.35 eV; (ii) Cu(I) aliovalent alloying leads to an absorption shoulder/peak at 4.8 eV and cyan photoluminescence (PL) peaked at 2.50 eV; (iii) Mn(II) isovalent alloying leads to weak Mn PL, which intensifies remarkably in the coalloyed samples, prompted by an energy transfer (ET) process between the Cu and Mn centers, favored by the overlap between the lowest (6A1 → 4T1) transition for tetrahedrally coordinated Mn2+ and the PL profile from Cu(I) species in the Cs3ZnCl5 NCs. The efficiency of this ET process reaches a value of 61% for the sample with the highest extent of Mn alloying. The PL quantum yield (QY) values in these Cu, Mn coalloyed NCs are lower at higher Mn contents. The analysis of the Mn PL dynamics in these samples indicates that this PL drop stems from inter-Mn exciton migration, which increases the likelihood of trapping in defect sites, in agreement with previous studies.

We elucidate here the nature of the emissive states in Rb7Sb3Cl16 nanocrystals (NCs) for which we report a synthesis. These NCs have a crystal structure comprising both isolated [SbCl6]3- octahedra and isolated [Sb2Cl10]4- dimers of octahedra. The optical properties of Rb7Sb3Cl16 NCs are compared with those of Sb-doped Rb3InCl6 NCs, the latter containing only isolated [SbCl6]3- octahedra. The remarkably similar behaviors of the two systems indicate that the optical emission in both materials originates from the isolated octahedra. Density functional theory calculations suggest that the [SbCl6]3- octahedra are optically active in emission because the local arrangement of the Rb+ ions around the octahedra limits the elongation of the Sb-Cl bonds upon excitation, helping to confine the self-trapped exciton in them. Conversely, in the [Sb2Cl10]4- dimers the constraining effect of the surrounding Rb+ ions is less marked and the Sb-Cl bonds fully break upon photoexcitation, opening up an efficient nonradiative channel for the self-trapped excitons.

We synthesize colloidal nanocrystals (NCs) of Rb3InCl6, composed of isolated metal halide octahedra (“0D”), and of Cs2NaInCl6 and Cs2KInCl6 double perovskites, where all octahedra share corners and are interconnected (“3D”), with the aim to elucidate and compare their optical features once doped with Sb3+ ions. Our optical and computational analyses evidence that the photoluminescence quantum yield (PLQY) of all these systems is consistently lower than that of the corresponding bulk materials due to the presence of deep surface traps from under-coordinated halide ions. Also, Sb-doped “0D” Rb3InCl6 NCs exhibit a higher PLQY than Sb-doped “3D” Cs2NaInCl6 and Cs2KInCl6 NCs, most likely because excitons responsible for the PL emission migrate to the surface faster in 3D NCs than in 0D NCs. We also observe that all these systems feature a large Stokes shift (varying from system to system), a feature that should be of interest for applications in photon management and scintillation technologies. Scintillation properties are evaluated via radioluminescence experiments, and re-absorption-free waveguiding performance in large-area plastic scintillators is assessed using Monte Carlo ray-tracing simulations.

We show here the first colloidal synthesis of double perovskite Cs2AgInCl6 nanocrystals (NCs) with a control over their size distribution. In our approach, metal carboxylate precursors and ligands (oleylamine and oleic acid) are dissolved in diphenyl ether and reacted at 105 °C with benzoyl chloride. The resulting Cs2AgInCl6 NCs exhibit the expected double perovskite crystal structure, are stable under air, and show a broad spectrum white photoluminescence (PL) with quantum yield of ∼1.6 ± 1%. The optical properties of these NCs were improved by synthesizing Mn-doped Cs2AgInCl6 NCs through the simple addition of Mn-acetate to the reaction mixture. The NC products were characterized by the same double perovskite crystal structure, and Mn doping levels up to 1.5%, as confirmed by elemental analyses. The effective incorporation of Mn ions inside Cs2AgInCl6 NCs was also proved by means of electron spin resonance spectroscopy. A bright orange emission characterized our Mn-doped Cs2AgInCl6 NCs with a PL quantum yield as high as ∼16 ± 4%.

We report here the synthesis of undoped and Cu-doped Cs2ZnCl4 nanocrystals (NCs) in which we could tune the concentration of Cu from 0.7 to 7.5%. Cs2ZnCl4 has a wide band gap (4.8 eV), and its crystal structure is composed of isolated ZnCl4 tetrahedra surrounded by Cs+ cations. According to our electron paramagnetic resonance analysis, in 0.7 and 2.1% Cu-doped NCs the Cu ions were present in the +1 oxidation state only, while in NCs at higher Cu concentrations we could detect Cu(II) ions (isovalently substituting the Zn(II) ions). The undoped Cs2ZnCl4 NCs were non emissive, while the Cu-doped samples had a bright intragap photoluminescence (PL) at similar to 2.6 eV mediated by band-edge absorption. Interestingly, the PL quantum yield was maximum (similar to 55%) for the samples with a low Cu concentration ([Cu] <= 2.1%), and it systematically decreased when further increasing the concentration of Cu, reaching 15% for the NCs with the highest doping level ([Cu] = 7.5%). The same (similar to 2.55 eV) emission band was detected under X-ray excitation. Our density functional theory calculations indicated that the PL emission could be ascribed only to Cu(I) ions: these ions promote the formation of trapped excitons, through which an efficient emission takes place. Overall, these Cu-doped Cs2ZnCl4 NCs, with their high photo- and radio-luminescence emission in the blue spectral region that is free from reabsorption, are particularly suitable for applications in ionizing radiation detection.

We devised a hot-injection synthesis to prepare colloidal double-perovskite Cs2NaBiCl6 nanocrystals (NCs). We also examined the effects of replacing Na+ with Ag+ cations by preparing and characterizing Cs2Na1–xAgxBiCl6 alloy NCs with x ranging from 0 to 1. Whereas Cs2NaBiCl6 NCs were not emissive, Cs2Na1–xAgxBiCl6 NCs featured a broad photoluminescence band at ∼690 nm, Stokes-shifted from the respective absorption by ≥1.5 eV. The emission efficiency was maximized for low Ag+ amounts, reaching ∼3% for the Cs2Na0.95Ag0.05BiCl6 composition. Density functional theory calculations coupled with spectroscopic investigations revealed that Cs2Na1–xAgxBiCl6 NCs are characterized by a complex photophysics stemming from the interplay of (i) radiative recombination via trapped excitons localized in spatially connected AgCl6–BiCl6 octahedra; (ii) surface traps, located on undercoordinated surface Bi centers, behaving as phonon-assisted nonradiative decay channels; and (iii) a thermal equilibrium between trapping and detrapping processes. These results offer insights into developing double-perovskite NCs with enhanced optoelectronic efficiency.

Metal halide perovskites represent a flourishing area of research, which is driven by both their potential application in photovoltaics and optoelectronics and by the fundamental science behind their unique optoelectronic properties. The emergence of new colloidal methods for the synthesis of halide perovskite nanocrystals, as well as the interesting characteristics of this new type of material, has attracted the attention of many researchers. This review aims to provide an up-to-date survey of this fast-moving field and will mainly focus on the different colloidal synthesis approaches that have been developed. We will examine the chemistry and the capability of different colloidal synthetic routes with regard to controlling the shape, size, and optical properties of the resulting nanocrystals. We will also provide an up-to-date overview of their postsynthesis transformations, and summarize the various solution processes that are aimed at fabricating halide perovskite-based nanocomposites. Furthermore, we will review the fundamental optical properties of halide perovskite nanocrystals by focusing on their linear optical properties, on the effects of quantum confinement, and on the current knowledge of their exciton binding energies. We will also discuss the emergence of nonlinear phenomena such as multiphoton absorption, biexcitons, and carrier multiplication. Finally, we will discuss open questions and possible future directions., ChemE/Opto-electronic Materials, QN/van der Zant Lab

We report the composition-dependent optical properties of Bi-doped Cs2Ag1-xNaxInCl6 nanocrystals (NCs) having a double perovskite crystal structure. Their photoluminescence (PL) was characterized by a large Stokes shift, and the PL quantum yield increased with the amount of Na up to ∼22% for the Cs2Ag0.4Na0.6InCl6 stoichiometry. The presence of Bi3+ dopants was crucial to achieve high PL quantum yields (PLQYs) as nondoped NC systems were not emissive. Density functional theory calculations revealed that the substitution of Ag+ with Na+ leads to localization of AgCl6 energy levels above the valence band maximum, whereas doping with Bi3+ creates BiCl6 states below the conduction band minimum. As such, the PL emission stems from trapped emission between states localized in the BiCl6 and AgCl6 octahedra, respectively. Our findings indicated that both the partial replacement of Ag+ with Na+ ions and doping with Bi3+ cations are essential in order to optimize the PL emission of these systems.

In this work, we demonstrate that a preferential Ga-for-Zn cation exchange is responsible for the increase in photoluminescence that is observed when gallium oleate is added to InZnP alloy QDs. By exposing InZnP QDs with varying Zn/In ratios to gallium oleate and monitoring their optical properties, composition, and size, we conclude that Ga3+ preferentially replaces Zn2+, leading to the formation of InZnP/InGaP core/graded-shell QDs. This cation exchange reaction results in a large increase of the QD photoluminescence, but only for InZnP QDs with Zn/In ≥ 0.5. For InP QDs that do not contain zinc, Ga is most likely incorporated only on the quantum dot surface, and a PL enhancement is not observed. After further growth of a GaP shell and a lattice-matched ZnSeS outer shell, the cation-exchanged InZnP/InGaP QDs continue to exhibit superior PL QY (over 70%) and stability under long-term illumination (840 h, 5 weeks) compared to InZnP cores with the same shells. These results provide important mechanistic insights into recent improvements in InP-based QDs for luminescent applications., ChemE/Opto-electronic Materials, QN/van der Zant Lab

Colloidal quantum dots (QDs) show great promise as LED phosphors due to their tunable narrow-band emission and ability to produce high-quality white light. Currently, the most suitable QDs for lighting applications are based on cadmium, which presents a toxicity problem for consumer applications. The most promising cadmium-free candidate QDs are based on InP, but their quality lags much behind that of cadmium based QDs. This is not only because the synthesis of InP QDs is more challenging than that of Cd-based QDs, but also because the large lattice parameter of InP makes it difficult to grow an epitaxial, defect-free shell on top of such material. Here, we propose a viable approach to overcome this problem by alloying InP nanocrystals with Zn2+ ions, which enables the synthesis of InxZnyP alloy QDs having lattice constant that can be tuned from 5.93 Å (pure InP QDs) down to 5.39 Å by simply varying the concentration of the Zn precursor. This lattice engineering allows for subsequent strain-free, epitaxial growth of a ZnSezS1-z shell with lattice parameters matching that of the core. We demonstrate, for a wide range of core and shell compositions (i.e.; varying x, y, and z), that the photoluminescence quantum yield is maximal (up to 60%) when lattice mismatch is minimal., Accepted Author Manuscript, ChemE/Opto-electronic Materials, QN/van der Zant Lab

Optical glassceramics are an important class of functional materials mainly employed in photonic and optoelectronic applications, as well as for advanced fiber optics. Here we present recent results on phase separation processes and optical properties of alkali germanosilicate glasses containing gallium oxide nanoparticles. Samples, with typical composition 7.5Li2O–2.5Na2O–20Ga2O3–35GeO2–35SiO2 (mol%), are obtained from the melt-quenching method. The resulting glasses are completely amorphous, but show phase separation, on the nanometer scale, deriving from liquid–liquid phase separation in the melt. Nanocrystallization of gallium oxide, in its metastable gamma phase, is thermally activated inside the matrix at about 615 °C. Treatment at higher temperature causes the formation of LiGa5O8 polymorph by Li ion diffusion from the surrounding matrix to the nanocrystals. In a second step, a further increment of temperature induces an order-to-disorder LiGa5O8 change that finally dissociates causing the formation of beta-Ga2O3. Neutron scattering, X-ray diffraction analysis, differential scanning calorimetry, and transmission electron microscopy studies have been performed so as to assess nucleation and crystal growth mechanisms. Parallel to morphological studies, we also present optical response of these systems, characterized by a strong UV-excited blue luminescence due to intrinsic defects and its dependence on thermal treatments. - See more at: http://www.european-mrs.com/2015-fall-symposium-w-european-materials-research-society#sthash.pRj5G4Gf.dpuf

The aim of this PhD project, also called “warm white light project”, is to propose an alternative solid state lighting device that works using the same principles of color-conversion WLEDs. The idea is to create a polymer based nanocomposite that could work as a transparent glass in off-mode and as a “lamp” in on-mode. The new concept is to spatially decouple the light source and the converters in order to avoid all the thermal problems that affect the current LEDs (in which the color is “generated” within the chip and the epoxy case). To do so, a blue LED, made of Indium gallium nitride (InGaN), is coupled to a bulk polymer nanocomposite sheet where the actual conversion of light takes place. For emitting white light it is necessary that the nanocomposite would not only convert partially the blue light into warmer colors (like yellow and red) but also diffuse the blue light outside in order to have a color mixing.

We report a new colloidal synthesis of niobium-doped TiO2 anatase nanocrystals (NCs) that allows for the preparation of ∼10 nm NCs with control over the amount of Nb doping up to ∼14%. The incorporation of niobium ions leads to the appearance of a tunable, broad absorption peak that ranges from the visible range to the mid-infrared. This optical behavior is attributed to the substitution of Nb5+ on Ti4+ sites generating free carriers inside the conduction band of the TiO2 NCs as supported by optical and electron paramagnetic resonance spectroscopic investigations. At the same time, the incorporation of progressively more niobium ions drives an evolution of the shape of the NCs from tetragonal platelets to "peanutlike" rods. © 2013 American Chemical Society.

Development of highly efficient and low cost LEDs makes possible to design lamps exploiting completely new concepts. In this perspective transparent polymer nanocomposites can play a fundamental role. In particular, a material that exhibits Rayleigh diffusion -i.e. having a scattering efficiency inversely proportional to the fourth power of the wavelength of light- is quite interesting for potential applications in the correction or introduction of color dispersion effects. Starting from Rayleighâ€TMs equation, considering all the basic characteristics of the nanocomposite (volume fraction of the nanoparticles, optical path of the light inside the diffuser, refractive indices of the components) and choosing as polymer matrix the paradigm of transparent polymers, polymethylmethacrylate (PMMA), it is possible to predict that a PMMA nanocomposite containing nanoparticles of inorganic oxides, transparent in the visible range and endowed with high refractive index (like TiO2 or ZnO), shows a marked effect of the Rayleighâ€TMs diffusion behavior when the dispersed nanoparticles present diameters comprised between 50 nm and 200 nm. Here we present the fabrication and characterization of such PMMA/TiO2 nanocomposites showing marked Rayleigh diffusion behavior. In a first step hydrophilic TiO2 rutile nanoparticles (116 nm average diameter) are converted to hydrophobic ones by modification of their surface by grafting of hexyl amine. The amount of attachment rate of surface-modifier on TiO2 nanoparticles is estimated by thermogravimetric analysis, while the structures of the modified titania surface are investigated by Solid-State NMR. Nanocomposites are fabricated as sheets (30 cm × 30 cm × 1 cm) by in situ polymerization of MMA containing the surface modified TiO2 nanoparticles. TEM measurements show homogeneous distribution of the nanoparticles in the PPMA matrix. Measurements of light transmittance in the visible range demonstrate that PMMA sheets containing between

We describe two synthesis approaches to colloidal Cu3P nanocrystals using trioctylphosphine (TOP) as phosphorus precursor. One approach is based on the homogeneous nucleation of small Cu3P nanocrystals with hexagonal plate-like morphology and with sizes that can be tuned from 5 to 50 nm depending on the reaction time. In the other approach, metallic Cu nanocrystals are nucleated first and then they are progressively phosphorized to Cu3P. In this case, intermediate Janus-like dimeric nanoparticles can be isolated, which are made of two domains of different materials, Cu and Cu3P, sharing a flat epitaxial interface. The Janus-like nanoparticles can be transformed back to single-crystalline copper particles if they are annealed at high temperature under high vacuum conditions, which makes them an interesting source of phosphorus. The features of the Cu Cu3P Janus-like nanoparticles are compared with those of the Wiped microstructure discovered more than two decades ago in the rapidly quenched Cu Cu3P eutectic of the Cu P alloy, suggesting that other alloy/eutectic systems that display similar behavior might give origin to nanostructures with flat, epitaxial Interface between domains of two diverse materials.Finally, the electrochemical properties of the copper phosphide plates are studied, and they are found to be capable of undergoing lithiation/delithiation through a displacement reaction, while the Janus-like Cu Cu3P particles do not display an electrochemical behavior that would make them suitable for applications in batteries.

We report a high-yield, low cost synthesis route to colloidal Cu1-xInS2 nanocrystals with a tunable amount of Cu vacancies in the crystal lattice. These are then converted into quaternary Cu-In-Zn-S (CIZS)nanocrystals by partial exchange of Cu+ and In3+ cations with Zn2+ cations. The photoluminescence quantum yield of these CIZS nanocrystals could be tuned up to a record 80\%, depending on the amount of copper vacancies.