Insights on Anisotropic Emission of (Diffused) Photo-Carriers in Hybrid Perovskite Microrods

Abstract

Quasi one-dimensional (1D) semiconductor materials with inherent anisotropic emission have numerous advantages in terms of brightness, color enhancement, and efficiency for optoelectronics and light-emitting devices. Herein, we report the anisotropic optical absorption and emission of individual methyl-ammonium lead bromide (MAPbBr 3 ) microrods (MRs). We find that the absorption and emission polarization direction is along the long axis of the MRs, and the degree of polarization (DOP) remains unaltered with the excitation field orientation as well as with the modulation in excitation energy. Polarization-resolved emission spectroscopy of individual MRs reveals that the orthogonally polarized fluorescence emissions originate from equivalent energy states, in contrast to other semiconductors rods. To explore the polarized PL emission behavior of the diffused photo-excited charge carriers, we employed an optical setup where MRs are locally excited at a confocal spot, and emission is imaged over the entire rod. Although photo-excited carriers in perovskites are known to have short initial polarization memory, we observe anisotropic emission far away, beyond several hundred nanometers from the excitation spot. This is remarkable and indicates strongly polarized radiative recombination of photogenerated carriers which migrate along the long axis of the crystals. Our measurements on single MRs in different dielectric media reveal that the electric field renormalization inside the crystal owing to dielectric changes at the interface is primarily responsible for such observed anisotropy in optical behaviors. The employed imaging method can potentially be used to explore the anisotropic emission behavior of photoexcited and diffused photo-carriers in various other semiconductor microcrystals with different material compositions, where excitation energy is transferred over long distances.

Lasing in perovskite crystallites grown via silver-nanowire-induced nucleation

“…4a, which suggests that the crystallites grown through the induction of Ag nanowires behaves well as an F-P cavity. [36][37][38] As shown in Fig. S7 (ESI †), we also tested the stability of MAPbBr 3 crystallites under the continuous irradiation of a 450 nm pulsed laser (5 ns, 10 Hz) in air.…”

Microscopic Perspective of Synergy between Localized Surface Plasmon Resonance and Disruption of Dye Aggregates in Metal Nanoparticle-Enhanced Fluorescence

“…For spatially resolved photoluminescence (PL) measurements of individual RB aggregates, we used a home-built inverted wide-field fluorescence microscopy setup; the details of optical arrangements can be found elsewhere. 43 In brief, a continuous wave (CW) 532 nm DPSS laser (Laserglow LRS-0532) was used to illuminate the prepared solid sample via an oil immersion objective lens (1.49 NA, 60X, Nikon, Apo TIRF). The excitation laser power was measured after the objective lens with a power meter (Lasercheck, Coherent) and was kept at ∼ 2 Wcm −2 for entire PL measurements.…”

“…The PL was recorded with an air-cooled sCMOS camera (sCMOS ORCA-Flash 4.0 V3, Hamamatsu) at 20 fps as a 16-bit TIFF files. For spatially resolved spectroscopy, we used a home-built spectrograph 43 to obtain a spectrally dispersed image recorded at 10 fps by the sCMOS detector. We flattened the background of the recorded movie before further analyses.…”