The mechanism responsible for the extremely long photoluminescence (PL) lifetimes observed in many lead halide perovskites is still under debate. While the presence of trap states is widely accepted, the process of electron detrapping back to the emissive state has been mostly ignored, especially from deep traps as these are typically associated with nonradiative recombination. Here, we study the photophysics of methylammonium lead bromide perovskite nanocrystals (PNCs) with a photoluminescence quantum yield close to unity. We show that the lifetime of the spontaneous radiative recombination in PNCs is as short as 2 ns, which is expected considering the direct bandgap character of perovskites. All longer (up to microseconds) PL decay components result from the rapid reversible processes of multiple trapping and detrapping of carriers with a slow release of the excitation energy through the spontaneous emission channel. As our modeling shows, the trap (dark) and excitonic states are coupled by the trapping–detrapping processes so that they follow the same population decay kinetics, while a majority of excited carriers are in the dark state. The lifetime of the PNCs delayed luminescence is found to be determined by the depth of the trap states, lying from a few tens to hundreds meV below the emitting excitonic state. The delayed luminescence model proposed in this work can serve as a basis for the interpretation of other photoinduced transient phenomena observed in lead halide perovskites.

The possibility of controlling light using the nonlinear optical properties of photonic devices opens new points of view in information and communications technology applications. In this Perspective, we review and analyze the potential role of metal halide perovskites in a framework different from their usual one in photovoltaic and light-emitting devices, namely, the one where they can play as nonlinear photonic materials. We contextualize this new role by comparing the few extant results on their nonlinear optical properties to those of other known nonlinear materials. As a result of this analysis, we provide a vision of future developments in photonics that can be expected from this new perspective on metal halide perovskites.

A perovskite–quantum dot exciplex has been detected, opening a broad range of possibilities for advanced optoelectronic devices.

The emission properties of hybrid halide perovskites are exploited to implement a stable and very low power operation waveguide optical amplifier integrated in a silicon platform. By optimizing its design with a poly(methyl methacrylate) (PMMA) encapsulation, this novel photonic device presents a net gain of around 10 dB cm−1 and 3–4 nm linewidth with an energy threshold as low as 2 nJ pulse−1 and exhibiting no degradation after one year.

In this paper, active planar waveguides based on the incorporation of CdSe and CdTe nanocrystal quantum dots in a polymer matrix are demonstrated. In the case of doping the polymer with both types of quantum dots, the nanocomposite film guides both emitted colors, green (550 nm, CdTe) and orange (600 nm, CdSe). The optical pumping laser can be coupled not only with a standard end-fire coupling system, but also directing the beam to the surface of the sample, indicating a good absorption cross-section and waveguide properties. To achieve these results, a study of the nanocomposite optical properties as a function of the nanocrystal concentration is presented and the optimum conditions are found for waveguiding.

Small (3-5 nm in diameter following HRTEM images) Si nanocrystals were produced in a two-stage process including (1) nanosecond laser ablation of a Si target in an organic liquid (chloroform) that results in formation of big composite polycrystalline particles (about 20-100 nm average diameter) and ( 2) ultrasonic post-treatment of Si nanoparticles in the presence of HF. The post-treatment is responsible for disintegration of the composite Si particles, release of small individual nanocrystals, and reduction of their size due to HF-induced etching of Si oxide. The downshift and broadening of the ∼520 cm -1 Raman phonon band of the small Si nanocrystals with respect to the bulk Si Raman band is consistent with the presence of ∼4.5 nm Si nanocrystals. The photoluminescence spectra (450-900 nm) and decay kinetics of small Si nanocrystals were detected, and the possible origin of the luminescence is discussed.

The efficiency of perovskite optoelectronic devices is increased by a novel method; its suitability for perovskite solar cells, light-emitting diodes, and optical amplifiers is demonstrated. The method is based on the introduction of organic additives during the anti-solvent step in the perovskite thin-film deposition process. Additives passivate grain boundaries reducing non-radiative recombination. The method can be easily extended to other additives.

Leuthold, J.; Hoessbacher, C.; Muehlbrandt, S.; Melikyan, A.; Kohl, M.; Koos, C.; Freude, W.; Dolores Calzadilla, V.M.; Smit, M.K.; Suarez, I.; Martin, A.; Martinez Pastor, J.; Fitrakis, E.P.; Tomkos, I. Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. J u e r g L e u t h o ld a n d c o ll e a g u e s J u e r g L e u t h o ld a n d c o ll e a g u e sSe e en d of ar tic le fo r fu ll au th or lis t.Illustations by Phil Saunders/spacechannel.org