| 1. |
- Eremchev, Ivan Yu, et al.
(författare)
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Detection of Single Charge Trapping Defects in Semiconductor Particles by Evaluating Photon Antibunching in Delayed Photoluminescence
- 2023
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992.
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Tidskriftsartikel (refereegranskat)abstract
- Time-resolved analysis of photon cross-correlation function g(2)(τ) is applied to photoluminescence (PL) of individual submicrometer size MAPbI3 perovskite crystals. Surprisingly, an antibunching effect in the long-living tail of PL is observed, while the prompt PL obeys the photon statistics typical for a classical emitter. We propose that antibunched photons from the PL decay tail originate from radiative recombination of detrapped charge carriers which were initially captured by a very limited number (down to one) of shallow defect states. The concentration of these trapping sites is estimated to be in the range 1013-1016 cm-3. In principle, photon correlations can be also caused by highly nonlinear Auger recombination processes; however, in our case it requires unrealistically large Auger recombination coefficients. The potential of the time-resolved g(2)(0) for unambiguous identification of charge rerecombination processes in semiconductors considering the actual number of charge carries and defects states per particle is demonstrated.
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| 2. |
- Eremchev, Ivan Yu, et al.
(författare)
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Lack of Photon Antibunching Supports Supertrap Model of Photoluminescence Blinking in Perovskite Sub-Micrometer Crystals
- 2021
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Ingår i: Advanced Optical Materials. - : Wiley. - 2195-1071. ; 9:3
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Tidskriftsartikel (refereegranskat)abstract
- Antibunching effect is typically observed in individual systems possessing photoluminescence (PL) blinking and vice versa. Contrary to this common perception, absence of antibunching in strongly blinking methyl ammonium led tri-iodide (MAPbI3) perovskite crystals of sizes from tens to hundreds of nanometers regardless of the excitation power density is observed. Antibunching effect does not appear even when photon statistics are analyzed for bright and intermediate PL intensity levels independently. This shows that there is no directional energy funneling and accumulation of charge carriers in the small local regions in MAPbI3 crystals where an Auger recombination can potentially suppress the simultaneous emission of two photons. This result allows for the exclusion of the PL blinking mechanism based on the idea of emitting sites previously hypothesized for perovskites. Therefore, the model of PL blinking in perovskite crystals based on the presence of a metastable non-radiative recombination center (the supertrap) is the only one proposed so far which explains blinking without conflicting with the absence of photon correlations.
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| 3. |
- Li, Jun, et al.
(författare)
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Tolerance of metal halide perovskites to mechanical treatment enables the fabrication of patterned luminescence nano- and microstructures
- 2022
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Ingår i: Materials Advances. - : Royal Society of Chemistry (RSC). - 2633-5409. ; 27:35
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites have shown a great performance in a broad range of optoelectronic devices. The variety of preparation methods makes perovskites especially attractive, yet preparation of complex nanostructures based on these materials remains challenging. Here we present a template assisted method allowing to achieve any pre-designed arrangement of methylammonium lead triiodide (MAPbI3) polycrystalline patterns with the spatial resolution defined by the template. We utilized a Si/SiO2 wafer with circular 180 nm deep recesses with diameters ranging from 200 to 1600 nm as a template. A polycrystalline perovskite powder was obtained by scratching off a thin perovskite film and mechanically introduced into the patterned template as a pigment. Scanning electron microscopy revealed that the recesses are filled with tightly packed sub-20 nm crystallites. Considering that the spin-coated film used as a source of MAPbI3 consisted of grains up to 2000 nm in diameter suggests that the initially prepared grains were crashed by rubbing to much smaller crystallites. In spite of this harsh mechanical treatment, the filled recesses showed a strong photoluminescence signal, demonstrating the applicability of this approach for the fabrication of diverse nanophotonic structures.
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| 4. |
- Luo, Xuhao, et al.
(författare)
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Intrinsic polarization-sensitive organic photodetector with self-assembled all-polymer heterojunction
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 121:23
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Tidskriftsartikel (refereegranskat)abstract
- Intrinsic polarization-sensitive photodetectors (IPPDs) have attracted considerable attention in recent years due to their simplicity in configuration, making them ideal candidates for compact and integrated polarization-sensitive sensing and imaging systems. Photoactive films with intrinsic optical anisotropy are necessary for IPPDs. This study reports an achievement of photoactive films based on all-polymer heterojunction films with in-plane optical anisotropy using a simple bottom-up self-assembly method. Both the donor (TQ1) and acceptor (N2200) polymers have the same spatial orientation with distinct anisotropy, approaching a dichroic ratio (DR) of 8. Polarization-sensitive light absorption is due to the uniaxially oriented polymer chains, which are dominated by lamellar packing with edge-on orientation. For IPPDs based on this anisotropic all-polymer heterojunction film, a photocurrent anisotropy was found with a polarized photocurrent ratio of 2.6. The detectivity of these IPPDs was found to be 1.9 × 1011 Jones (@ ∼600 nm, 0 V bias). Our work shows that oriented polymer donor-acceptor films fabricated using bottom-up self-assembly have great potential in applications, such as polarization detection.
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| 5. |
- Bartholomew, John G., et al.
(författare)
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High-resolution spectroscopic techniques for studying rare-earth ions in nanoparticles
- 2023
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Ingår i: Journal of Luminescence. - : Elsevier BV. - 0022-2313. ; 257
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Tidskriftsartikel (refereegranskat)abstract
- Rare-earth doped nanoparticles can exhibit narrow optical and spin linewidths at low temperatures. These outstanding properties for nanomaterials make them attractive for quantum technologies based on optically addressable spins such as quantum memories and computers. Although accurate linewidth measurements have been reported using, for example, spectral hole burning or photon echo techniques, so far they have been mostly restricted to large ensembles of particles. Being able to extend linewidths measurements to few and single particles is particularly important in view of their integration in nanophotonic devices. In this paper, we present techniques for determining inhomogeneous and homogeneous linewidths of small ensembles of rare-earth ions in doped nanoparticles with high signal-to-noise ratios for convenient integration times. Using these techniques we have observed property variations for particles from the same synthesis, a first step towards their optimization for applications in quantum technologies.
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| 6. |
- Bresolí-Obach, Roger, et al.
(författare)
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Resonantly Enhanced Optical Trapping of Single Dye-Doped Particles at an Interface
- 2021
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Ingår i: ACS Photonics. - : American Chemical Society (ACS). - 2330-4022. ; 8:6, s. 1832-1839
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Tidskriftsartikel (refereegranskat)abstract
- The optical resonance between an absorbing particle and the trapping laser can enhance the radiation force exerted on micro/nanoscale objects. However, the exact mechanism behind this resonance is still elusive. To unravel the phenomenon, we studied the resonance between a single dye-doped polystyrene particle and a 1064 nm trapping laser under specifically designed optical conditions. The dye-doped particle was trapped at a water-glass interface while simultaneously being excited by a 488 nm widefield laser. In contrast with former reports (â 10-35% trapping stiffness enhancement), we obtained an unprecedented 4-fold trapping stiffness enhancement due to resonant excitation. When we photobleached the embedded dyes as a control, the trapping stiffness enhancement was no longer observed. Based on nonlinear resonant radiation force theory and the experimental data obtained with a three-dimensional multiplane microscope, we propose that the widefield laser excites the dye to S1 and the trapping laser induces a simultaneous ultrafast S1-S2-S1 cyclic transition, resonantly enhancing the induced dye polarization and, consequently, the radiation force. The elucidation of the optical resonance effect is expected to ultimately enable single molecule manipulation in solution at room temperature.
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| 7. |
- Camacho, Rafael, et al.
(författare)
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Fluorescence Anisotropy Reloaded—Emerging Polarization Microscopy Methods for Assessing Chromophores' Organization and Excitation Energy Transfer in Single Molecules, Particles, Films, and Beyond
- 2019
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 31:22
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Forskningsöversikt (refereegranskat)abstract
- Fluorescence polarization is widely used to assess the orientation/rotation of molecules, and the excitation energy transfer between closely located chromophores. Emerging since the 1990s, single molecule fluorescence spectroscopy and imaging stimulate the application of light polarization for studying molecular organization and energy transfer beyond ensemble averaging. Here, traditional fluorescence polarization and linear dichroism methods used for bulk samples are compared with techniques specially developed for, or inspired by, single molecule fluorescence spectroscopy. Techniques for assessing energy transfer in anisotropic samples, where the traditional fluorescence anisotropy framework is not readily applicable, are discussed in depth. It is shown that the concept of a polarization portrait and the single funnel approximation can lay the foundation for alternative energy transfer metrics. Examples ranging from fundamental studies of photoactive materials (conjugated polymers, light-harvesting aggregates, and perovskite semiconductors) to Förster resonant energy transfer (FRET)-based biomedical imaging are presented. Furthermore, novel uses of light polarization for super-resolution optical imaging are mentioned as well as strategies for avoiding artifacts in polarization microscopy.
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| 8. |
- Chen, Ruiyun, et al.
(författare)
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Creation and Annihilation of Nonradiative Recombination Centers in Polycrystalline Metal Halide Perovskites by Alternating Electric Field and Light
- 2020
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Ingår i: Advanced Optical Materials. - : Wiley. - 2195-1071. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- Metal halide perovskites are promising optoelectronic materials. Their electronic properties however are rather unstable which is often assigned to ion migration. Ion migration can be readily influenced by an electric field (EF). Here, the response of photoluminescence (PL) of individual MAPbX3 (MA = CH3NH3, X = I, Br) sub-micrometer-sized polycrystals to EF is studied. Alternating EF with frequency higher than 10 Hz is found to reversibly quench PL. It is proposed that an alternating EF when applied together with light increases ion migration. This leads to a shift in the equilibrium between creation and annihilation of defects toward higher concentration of nonradiative recombination centers. The PL quenching is found to increase with increasing frequency of the field. This can be rationalized by the frequency dependence of the dielectric constant, leading to stronger internal fields for high modulation frequencies compared to, e.g., a constant EF with the same external amplitude. PL quenching and enhancement observed under constant EF are hypothesized to be due to a reconfiguration of already existing nonradiative recombination centers situated on grain boundaries. The control of perovskite PL by alternating EF reported here can find applications in optoelectronic devices.
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| 9. |
- Dobrovolsky, Alexander, et al.
(författare)
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Defect-induced local variation of crystal phase transition temperature in metal-halide perovskites
- 2017
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Solution-processed organometal halide perovskites are hybrid crystalline semiconductors highly interesting for low-cost and efficient optoelectronics. Their properties are dependent on the crystal structure. Literature shows a variety of crystal phase transition temperatures and often a spread of the transition over tens of degrees Kelvin. We explain this inconsistency by demonstrating that the temperature of the tetragonal-to-orthorhombic phase transition in methylammonium lead triiodide depends on the concentration and nature of local defects. Phase transition in individual nanowires was studied by photoluminescence microspectroscopy and super-resolution imaging. We propose that upon cooling from 160 to 140 K, domains of the crystal containing fewer defects stay in the tetragonal phase longer than highly defected domains that readily transform to the high bandgap orthorhombic phase at higher temperatures. The existence of relatively pure tetragonal domains during the phase transition leads to drastic photoluminescence enhancement, which is inhomogeneously distributed across perovskite microcrystals.
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| 10. |
- Dobrovolsky, Alexander, et al.
(författare)
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Relating Defect Luminescence and Nonradiative Charge Recombination in MAPbI3 Perovskite Films
- 2020
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Ingår i: Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 11:5, s. 1714-1720
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Tidskriftsartikel (refereegranskat)abstract
- Nonradiative losses in semiconductors are related to defects. At cryogenic temperatures, defect-related photoluminescence (PL) at energies lower than the band-edge PL is observed in methylammonium lead triiodide perovskite. We applied multispectral PL imaging to samples prepared by two different procedures and exhibiting 1 order of magnitude different PL quantum yield (PLQY). The high-PLQY sample showed concentration of the emitting defect sites around 1012-1013 cm-3. No correlation between PLQY and the relative intensity of the defect emission was found when micrometer-sized local regions of the same sample were compared. However, a clear positive correlation between the lower PLQY and higher defect emission was observed when two preparation methods were contrasted. Therefore, although the emissive defects are not connected directly with the nonradiative centers and may be spatially separated at the nano scale, chemical processes during the perovskite synthesis promote/prevent formation of both types of defects at the same time.
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