Recruiting Unicellular Algae for the Mass Production of Nanostructured Perovskites.

Functional capacities of lead halide perovskites are strongly dependent on their morphology, crystallographic texture, and internal ultrastructure on the nano- and the meso-scale. In the last decade, significant efforts are directed towards the development of novel synthesis routes that would overcome the morphological constraints provided by the physical and crystallographic properties of these materials. In contrast, various living organisms, such as unicellular algae, have the ability to mold biogenic crystals into a vast variety of intricate nano-architectured shapes while keeping their single crystalline nature. Here, using the cell wall of the dinoflagellate L. granifera as a model, sustainably harvested biogenic calcite is successfully transformed into nano-structured perovskites. Three variants of lead halide perovskites CH3 NH3 PbX3 are generated with X = Cl- , Br- and I- ; exhibiting emission peak-wavelength ranging from blue, to green, to near-infrared, respectively. The approach can be used for the mass production of nano-architectured perovskites with desired morphological, textural and, consequently, physical properties exploiting the numerous templates provided by calcite forming unicellular organisms.

Controlling and Optimizing Amplified Spontaneous Emission in Perovskites.

Perovskites are currently attracting extensive research interest as a wavelength-tunable lasing material. As a first step toward electrically pumped lasers, numerous investigations have recently reported amplified spontaneous emission (ASE) of optically pumped perovskites with remarkably low thresholds. Here, we investigate the optical aspects of perovskite ASE, to establish the design principle of materials and devices. We show that compared to solution-processed CsPbBr3, vacuum deposition yields superior ASE characteristics with a threshold of 35 µJ/cm2. The optical loss (Rloss) during lateral photon propagation in the waveguide mode is identified as a key parameter to determine the ASE quality. With spatially resolved photoluminescence, we determine Rloss as 40 and >1000 cm-1 for vacuum and solution-processed perovskites, respectively. We present a comprehensive model that relates ASE, gain length, optical loss, temperature, and density of states. Finally, we succeed in demonstrating ASE in perovskite samples with metal electrodes, mimicking a diode architecture for electrical pumping. Optical spacer layers are shown to play a crucial role in preventing metal absorption loss in waveguide modes.

Microcavity Laser Based on a Single Molecule Thick High Gain Layer.

The ability to confine excitons within monolayers has led to fundamental investigations of nonradiative energy transfer, super-radiance, strong light-matter coupling, high-efficiency light-emitting diodes, and recently lasers in lateral resonator architectures. Vertical cavity surface emitting lasers (VCSELs), in which lasing occurs perpendicular to the device plane, are critical for telecommunications and large-scale photonics integration, however strong optical self-absorption and low fluorescence quantum yields have thus far prevented coherent emission from a monolayer microcavity device. Here we show lasing from a monolayer VCSEL using a single molecule thick film of amphiphilic fluorescent dye, assembled via Langmuir-Blodgett deposition, as the gain layer. Threshold was observed when 5% of the molecules were excited (4.4 µJ/cm2). At this level of excitation, the optical gain in the monolayer exceeds 1056 cm-1. High localization of the excitons in the VCSEL gain layer can enhance their collective emission properties with Langmuir-Blodgett deposition presenting a paradigm for engineering the high gain layers on the molecular level.

Strong Light-Matter Coupling and Hybridization of Molecular Vibrations in a Low-Loss Infrared Microcavity.

Hybridized polaritons are generated by simultaneously coupling two vibrational modes of two different organic materials to the resonance of a low-loss infrared optical microcavity. A thin film of poly methyl methacrylate with solvent molecules of dimethylformamide trapped inside provided two spectrally narrow, closely spaced carbonyl stretches with absorption peaks at 1731 and 1678 cm(-1). Situating this film in a microcavity based on Ge/ZnS distributed Bragg reflector mirrors produced three distinct polariton branches in the dispersion relation due to hybridization of the vibrational resonances. Two anticrossings were observed with Rabi splittings of 9.6 and 5.2 meV, between the upper-to-middle and middle-to-lower polariton branches, respectively. This system marks the first demonstration of polariton hybridization between a solid and solvent molecules and can open new paths toward chemical reaction modification and energy transfer studies in the mid-infrared spectral range.