There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Lead halide perovskites (LHPs) in the form of nanometre-sized colloidal crystals, or nanocrystals (NCs), have attracted the attention of diverse materials scientists due to their unique optical versatility, high photoluminescence quantum yields and facile synthesis. LHP NCs have a 'soft' and predominantly ionic lattice, and their optical and electronic properties are highly tolerant to structural defects and surface states. Therefore, they cannot be approached with the same experimental mindset and theoretical framework as conventional semiconductor NCs. In this Review, we discuss LHP NCs historical and current research pursuits, challenges in applications, and the related present and future mitigation strategies explored.

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Genesis, challenges and opportunities for colloidal lead halide perovskite nanocrystals

The synthesis, crystal growth, and structural and optoelectronic characterization has been carried out for the perovskite compound CsPbBr3. This compound is a direct band gap semiconductor which meets most of the requirements for successful detection of X- and γ-ray radiation, such as high attenuation, high resistivity, and significant photoconductivity response, with detector resolution comparable to that of commercial, state-of-the-art materials. A structural phase transition which occurs during crystal growth at higher temperature does not seem to affect its crystal quality. Its μτ product for both hole and electron carriers is approximately equal. The μτ product for electrons is comparable to cadmium zinc telluride (CZT) and that for holes is 10 times higher than CZT.

Crystal Growth of the Perovskite Semiconductor CsPbBr3: A New Material for High-Energy Radiation Detection

Metal halide perovskites represent a flourishing area of research, driven by both their potential application in photo-voltaics and optoelectronics, and for the fundamental science underpinning their unique optoelectronic properties. The advent of colloidal methods for the synthesis of halide perovskite nanocrystals has brought to the attention inter-esting aspects of this new type of materials, above all their defect-tolerance. This review aims to provide an updated survey of this fast-moving field, with a main focus on their colloidal synthesis. We examine the chemistry and the ca-pability of different colloidal synthetic routes to control the shape, size and optical properties of the resulting nano-crystals. We also provide an up to date overview of their post-synthesis transformations, and summarize the various so-lution processes aimed at fabricating halide perovskite-based nanocomposites. We then review the fundamental optical properties of halide perovskite nanocrystals, by focusing on their linear optical properties, on the effects of quantum confinement and, then, on the current knowledge of their exciton binding energies. We also discuss the emergence of non-linear phenomena such as multiphoton absorption, biexcitons and carrier multiplication. At last, we provide an outlook in the field, with the most cogent open questions and possible future directions.

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications and Their Optical Properties

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...

Metal Halide Perovskite Nanocrystals: Synthesis, Post-Synthesis Modifications, and Their Optical Properties.

The cover picture of the current issue refers to the Rapid Research Letter by Martin Nikl et al. [1]. It depicts the structure of a Lu3Al5O12:Ce single crystal, a possible high performance scintillator material. Its scintillation performance is, however, degraded by the occurrence of antisite defects. Such defects arise in the material structure sketched in the figure due to the occurrence of Lu3+ ions at the Al3+ octahedral sites as seen in the middle left octahedron. This defect constitutes a shallow electron trap, which delays energy delivery to the Ce3+ emission centers, and thus slows down the scintillation response of the material. Thermoluminescence measurements appear as sensitive diagnostic tool to evidence these defects in the single crystals grown.



Martin Nikl is senior scientist and head of the Laboratory of Luminescence and Scintillation Materials at the Institute of Physics of the Czech Academy of Sciences. His main research activities include the characterization of the luminescence and scintillation properties of wide band-gap materials and the influence of material defects on them.

The antisite LuAl defect‐related trap in Lu3Al5O12:Ce single crystal

Excitonic emission of scheelite tungstates AWO4 (A=Pb, Ca, Ba, Sr)

Thermally stimulated luminescence (TSL) glow curves and emission spectra were studied in undoped and Ce-doped ${\mathrm{Lu}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ single crystals by wavelength resolved TSL measurements in the $10\char21{}310\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ temperature range. Isothermal phosphorescence measurements in the $10\char21{}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ range were also performed, which point to the existence of a tunneling-driven radiative recombination process. These processes can explain the presence and time-dependence of the submicrosecond slow decay component in the scintillation decay. Electron paramagnetic resonance experiments suggest the presence of ${\mathrm{Lu}}_{\mathrm{Al}}$ defects in the vicinity of ${\mathrm{Ce}}^{3+}$ ions, which are the most probable electron and hole traps participating in the tunneling-driven radiative recombination process.

E. Mihokova

Papers

The antisite LuAl defect‐related trap in Lu3Al5O12:Ce single crystal

Excitonic emission of scheelite tungstates AWO4 (A=Pb, Ca, Ba, Sr)

Shallow traps and radiative recombination processes in Lu3Al5O12:Ce single crystal scintillator

Luminescence and scintillation properties of YAG:Ce single crystal and optical ceramics

Photoluminescence of Cs4PbBr6 crystals and thin films