Unusual Spectrally Reproducible and High Q-Factor Random Lasing in Polycrystalline Tin Perovskite Films.

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 to Sn oxidation. Remarkably, a quality Q-factor as high as ≈10 with an amplified spontaneous emission (ASE) threshold as low as 2 µJ cm (both at 20 K) are achieved. The observed spectral reproducibility is unprecedented for semiconductor thin film RL systems and cannot be explained by the strong spatial localization of lasing modes.

Tin perovskite solar cells with >1,300 h of operational stability in N through a synergistic chemical engineering approach.

Despite the promising properties of tin-based halide perovskites, one clear limitation is the fast Sn oxidation. Consequently, the preparation of long-lasting devices remains challenging. Here, we report a chemical engineering approach, based on adding Dipropylammonium iodide (DipI) together with a well-known reducing agent, sodium borohydride (NaBH), aimed at preventing the premature degradation of Sn-HPs.

Inhomogeneous Broadening of Photoluminescence Spectra and Kinetics of Nanometer-Thick (Phenethylammonium)PbI Perovskite Thin Films: Implications for Optoelectronics.

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.

White light emission from lead-free mixed-cation doped CsSnCl nanocrystals.

We have designed a synthesis procedure to obtain CsSnCl nanocrystals (NCs) doped with metal ion(s) to emit visible light. CsSnCl NCs doped with Bi, Te and Sb ions emitted blue, yellow and red light, respectively. In addition, NCs simultaneously doped with Bi and Te ions were synthesized in a single run.

Purcell Enhancement and Wavelength Shift of Emitted Light by CsPbI Perovskite Nanocrystals Coupled to Hyperbolic Metamaterials.

Manipulation of the exciton emission rate in nanocrystals of lead halide perovskites (LHPs) was demonstrated by means of coupling of excitons with a hyperbolic metamaterial (HMM) consisting of alternating thin metal (Ag) and dielectric (LiF) layers. Such a coupling is found to induce an increase of the exciton radiative recombination rate by more than a factor of three due to the Purcell effect when the distance between the quantum emitter and HMM is nominally as small as 10 nm, which coincides well with the results of our theoretical analysis. Besides, an effect of the coupling-induced long wavelength shift of the exciton emission spectrum is detected and modeled.

Single-Exciton Amplified Spontaneous Emission in Thin Films of CsPbX (X = Br, I) Perovskite Nanocrystals.

CsPbX perovskite nanocrystals (PNCs) have emerged as an excellent material for stimulated emission purposes, with even more prospective applications than conventional colloidal quantum dots. However, a better understanding of the physical mechanisms responsible for amplified spontaneous emission (ASE) is required to achieve more ambitious targets (lasing under continuous wave optical or electrical excitation). Here, we establish the intrinsic mechanisms underlying ASE in PNCs of three different band gaps (CsPbBr, CsPbBrI, and CsPbI).

Short Photoluminescence Lifetimes in Vacuum-Deposited CHNHPbI Perovskite Thin Films as a Result of Fast Diffusion of Photogenerated Charge Carriers.

It is widely accepted that a long photoluminescence (PL) lifetime in metal halide perovskite films is a crucial and favorable factor, as it ensures a large charge diffusion length leading to a high power conversion efficiency (PCE) in solar cells. It has been recently found that vacuum-evaporated CHNHPbI (eMAPI) films show very short PL lifetimes of several nanoseconds. The corresponding solar cells, however, have high photovoltage (>1.

Formation of Si/SiO Luminescent Quantum Dots From Mesoporous Silicon by Sodium Tetraborate/Citric Acid Oxidation Treatment.

We propose a rapid, one-pot method to generate photoluminescent (PL) mesoporous silicon nanoparticles (PSiNPs). Typically, mesoporous silicon (meso-PSi) films, obtained by electrochemical etching of monocrystalline silicon substrates, do not display strong PL because the silicon nanocrystals (nc-Si) in the skeleton are generally too large to display quantum confinement effects. Here we describe an improved approach to form photoluminescent PSiNPs from meso-PSi by partial oxidation in aqueous sodium borate (borax) solutions.

Incorporation of potassium halides in the mechanosynthesis of inorganic perovskites: feasibility and limitations of ion-replacement and trap passivation.

Potassium halides (KX; X = I, Br, or Cl) were incorporated as partial replacements of CsBr in the mechanosynthesis of CsPbBr. This led to partial substitution of both monovalent ions forming mixed Cs K PbBr X perovskites. Longer photoluminescence lifetimes were also observed, possibly linked to the formation of a non-perovskite KPbX passivating layer.

Photophysical characterization of oligopyrene modules for DNA-based nanosystems.

The photophysics of free pyrenedicarboxamide (Py-DCA) in solution as well as of single-stranded and double-stranded oligonucleotides (ss and ds ONs) containing 1-7 pyrene building blocks per strand were studied by steady-state and time-resolved fluorescence spectroscopy. It was found that the fluorescence quantum yield Phi(F) of free Py-DCA chromophore in solution is rather high (Phi(F) = 0.44).

Photoinduced axial ligation and deligation dynamics of nonplanar nickel dodecaarylporphyrins.

The ground- and excited-state metal-ligand dynamics of nonplanar nickel(II) 2,3,5,7,8,10,12,13,15,17,18,20-dodecaphenylporphyrin (NiDPP) and two fluorinated analogues (NiF(20)DPP and NiF(28)DPP) have been investigated using static and time-resolved absorption spectroscopy in toluene and in ligating media that differ in basicity, aromaticity, and steric encumbrance. Because of the electronic and steric consequences of nonplanarity, NiDPP does not bind axial ligands in the ground state, but metal coordination does occur after photoexcitation with multistep dynamics that depend on the properties of the ligand. Following the structural relaxations that occur in all nickel porphyrins within approximately 10 ps, ligand binding to photoexcited NiDPP is progressively longer in pyridine, piperidine, and 3,5-lutidine (25-100 ps) but does not occur at all in 2,6-lutidine in which the ligating nitrogen is sterically encumbered.