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Author to whom correspondence should be addressed;E-Mail: Emmanuelle.Deleporte@lpqm.ens-cachan.fr; Tel.: +33147407591; Fax: +33147402465.Received: 20 March 2010; in revised form: 7 May 2010 / Accepted: 18 May 2010 /Published: 25 May 2010Abstract: This article reviews the synthesis, structural and optical characterizations of somenovel luminescent two dimensional organic-inorganic perovskite (2DOIP) semiconductors.These 2DOIP semiconductors show a self-assembled nano-layered structure, having theelectronic structure of multi-quantum wells. 2DOIP thin layers and nanoparticles havebeen prepared through different methods. The structures of the 2DOIP semiconductors arecharacterized by atomic force microscopy and X-ray diffraction. The optical properties of the2DOIP semiconductors are characterized from absorption and photoluminescence spectrameasured at room and low temperatures. Influences of different components, in particularthe organic parts, on the structural and optical properties of the 2DOIP semiconductors arediscussed.

We have realized several one-dimensional (1D) microcavities, containing self-assembled perovskite layers, emitting in the ultraviolet (UV) range (around 3.5 eV), working in the strong-coupling regime at room temperature. Procedures to increase the quality factor of the microcavities have been explored. Two different technologies have to be combined: the soft technologies related to the organic materials and polymers and the technologies which are more specific to inorganic materials, such as electron-beam evaporation and sputtering, used in particular to deposit dielectric mirrors.

The molecular crystal of ( C 6 H 5 C 2 H 4 – NH 3 ) 2 PbCl 4 perovskite presents an excitonic state with an absorption energy in the ultraviolet range (3.64 eV, 341 nm) and a large binding energy (few hundred of meV). We report here on the realization of a Perot–Fabry λ -microcavity containing a thin film of this material as active layer. Angle-resolved reflectivity and photoluminescence measurements demonstrate this microcavity works, at room temperature, in the strong coupling regime: the cavity photon mode and the excitonic state are not eigenmodes of the system any more, the new eigenmodes are a linear and coherent superposition of the exciton and photon states, called cavity polaritons.

We report on the synthesis of some novel organic–inorganic hybrid 2D perovskite semiconductors (R-(CH2)nNH3)2PbX4. These semiconductors are self-assembled intercalation nanolayers and have a multi-quantum-well energy level structure. We systematically vary the characteristic of organic groups (R-(CH2)n NH 3 + ) to study the relationship between their structures and the optical properties of (R-(CH2)nNH3)2PbX4. From optical absorption and photoluminescence spectroscopy experiments performed on series of samples, we find some trends of choosing the organic groups to improve the optical performance of (R-(CH2)nNH3)2PbX4. A new organic group, which allows synthesis of nanolayer perovskite semiconductors with quite high photoluminescence efficiency and better long-term stability, has been found.

New large size luminescent nanoparticles have been prepared, based on lead bromide or iodide organic perovskites. The luminescent center is made of PbX42− octahedrons. The preparation of the nanoparticles stems from fast nebulization and subsequent lyophilization of perovskite DMF solutions. The particles described have an average size of 60 nm, but a 20−500 nm range is in principle accessible. These new nanoparticles constitute an alternative to Q-dots which allows variable size while retaining the same emission wavelength, like silica particles functionalized with organic dyes, but with a higher stability under illumination.

National audience

International audience; We focus here our attention on a particular family of 2D-layered and 3D hybrid perovskite molecular crystals, the mixed perovskites (C6H5–C2H4–NH3)2PbZ4(1–x)Y4x and (CH3–NH3)PbZ3(1–x)Y3x, where Z and Y are halogen ions such as I, Br, and Cl. Studying experimentally the disorder-induced effects on the optical properties of the 2D mixed layered materials, we demonstrate that they can be considered as pseudobinary alloys, exactly like Ga1–xAlxAs, Cd1–xHgxTe inorganic semiconductors, or previously reported 3D mixed hybrid perovskite compounds. 2D-layered and 3D hybrid perovskites afford similar continuous optical tunability at room temperature. Our theoretical analysis allows one to describe the influence of alloying on the excitonic properties of 2D-layered perovskite molecular crystals. This model is further refined by considering different Bohr radii for pure compounds. This study confirms that despite a large binding energy of several 100 meV, the 2D excitons present a Wannier character rather than a Frenkel character. The small inhomogeneous broadening previously reported in 3D hybrid compounds at low temperature is similarly consistent with the Wannier character of free excitons.

International audience; We report on the realization of monolithic optical microcavities using a single wall carbon nanotubes doped polymer as active material. Thanks to the control of the polymer thickness, a ne control of the cavity mode energy is achieved, which allows to tune it in exact resonance with a speci c chiral species emission line. The quality factor of the lled cavity mode (Q = 40) allows to selectively extract the luminescence of the (7,5) chiral species. Finally, angle resolved experiments show the tunability of the emission energy within a 150 meV range.

Due to their high potentiality for photovoltaic applications or coherent light sources, a renewed interest in hybrid organic perovskites has emerged for few years. When they are arranged in two dimensions, these materials can be considered as hybrids quantum wells. One consequence of the unique structure of 2D hybrid organic perovskites is a huge exciton binding energy that can be tailored through chemical engineering. We present experimental investigations of the exciton nonlinearities by means of femtosecond pump-probe spectroscopy. The exciton dynamics is fitted with a bi-exponential decay with a free exciton life-time of ~100 ps. Moreover, an ultrafast intraband relaxation (< 150 fs) is also reported. Finally, the transient modification of the excitonic line is analysed through the momenta analysis and described in terms of reduction of the oscillator strength and linewidth broadening. We show that excitonic non-linearities in 2D hybrid organic perovskites share some behaviours of inorganic semiconductors despite their huge exciton binding energy.

We realize a Fabry-Perot hybrid microcavity containing an association of a ZnO thin layer and of a layer of the two-dimensional layered perovskite 5-methyl-2-furanmethanamonium lead bromide (MFMPB). From angle-resolved reflectivity experiments performed at low temperature of 5 K, we show that this hybrid cavity works in the strong-coupling regime and that the lower, middle, and upper polariton branches are observed. We show that the middle polariton branch (MPB) contains a significant component of the cavity photon and both of the two exciton species.

We report on optical spectroscopy (photoluminescence and photoluminescence excitation) on two-dimensional self-organized layers of $(C_{6}H_{5}C_{2}H_{4}-NH_{3})_{2}PbI_{4}$ perovskite. Temperature and excitation power dependance of the optical spectra gives a new insight into the excitonic and phononic properties of this hybrid organic/inorganic semiconductor. In particular, exciton-phonon interaction is found to be more than one order of magnitude higher than in GaAs QWs. As a result, photoluminescence emission lines have to be interpreted in the framework of a polaron model.

International audience; We report on the realization of a molecule-based one-dimensional microcavity emitting in the near UV range at room temperature. The active material is a thin film of the two-dimensional perovskite C6H5C2H4–NH32PbCl4, a molecular compound absorbing and emitting light around 3.6 eV. Angle-resolved reflectivity and photoluminescence measurements show that this microcavity works in the strong coupling regime. The emitting UV polariton is a mixed state between the photon cavity mode and the exciton of the perovskite-type semiconductor.

International audience; We have realized Perot–Fabry microcavities containing a twodimensional layered perovskite-type semiconductor: (C6H5C2H4–NH3)2PbI4 between a dielectric mirror and a metallic mirror. A strong coupling regime between the perovskite exciton and the confined photon mode has been evidenced at room temperature from angular-resolved reflectivity experiments, anticrossings as large as 190 meV are observed between the excitonic and cavity modes. We have shown that the design of the microcavity can be varied at will, so that the detuning or the Rabi splitting can be precisely chosen. The emission of the polaritonic low energy branch has been observed.