Observation of Nonlinear Emission Dynamics in a Quasi-Two-Dimensional Perovskite Crystal By Femtosecond Transient Absorption Microscopy
Authors: Katayama Tetsuro , Furube Akihiro 
Published: December 2024

INTRODUCTION

The phenomenon of superfluorescence using photoexcitation followed by induced synchronization of the dipoles is important not only from the fundamental viewpoint of understanding the interaction between light and matter but also from the applied viewpoint of realizing the miniaturization of light sources. Organic-inorganic lead halide perovskite materials have various attractive properties not only for solar cells but also for LED and nanoscale lasers because of their wavelength tunability and low lasing threshold. Such an efficient lasing is indispensable for their applications, and the essential needs are miniaturization and low threshold, especially for quasi-2D systems[1]. In this study, we aim to fabricate quasi-two-dimensional perovskite crystals and observe superfluorescence phenomenon by transient absorption microscopy.

EXPERIMENTAL SECTION

110 mg of lead bromide, 70 mg of cesium bromide, and 24 mg of phenethyl ammonium bromide were dissolved in 3 mL of dimethyl sulfoxide and the solution was sealed in a spray vial under a nitrogen atmosphere. Then spray was applied onto a cover glass under a nitrogen atmosphere, and crystals were allowed to grow under isopropanol vapor for 8 min at 50°C.
Transient absorption microscopy setup was the system previously reported[2]. A regenerative amplified Ti: sapphire laser (Solstice, Spectra-Physics, 1 kHz, 795 nm, output power about 3.5 W) was a light source. The 795 nm fundamental beam output from the regenerative amplifier was then split into two equal intensities by a beam splitter, and output light was obtained from an optical parametric amplifier (OPA, TOPAS, light-conversion). The signal light (1.3 μm) guided from OPA was directed onto an amorphous CaF2 plate to generate white light. This white light was divided into two parts by a half-mirror. A portion of the white light was transmitted to the sample on the microscope as the monitoring light. And the other part was used as the reference light. Both the monitoring and reference lights were guided into a multichannel spectrometer (Orca quest) for spectral analysis. The reference light is to correct the intensity fluctuation of the white light. Excitation light was generated from a home-built non-collinear OPA (NOPA) at 550 nm and introduced to the microscope. The temporal resolution was ca. 150 fs.

RESULTS AND DISCUSSION

The excitation light intensity dependence of the emission spectrum of a quasi-two-dimensional perovskite crystal was measured with a femtosecond 400 nm excitation. A new emission maximum is observed above 173 mJ/cm2. To clarify the origin of this emission, the femtosecond transient absorption spectrum was measured (Exc. 400 nm). The time profiles of transient absorbance at 526 nm show a positive signal in the early stage and a negative signal over 1 ps in a single quasi-two-dimensional perovskite crystal. The positive signal suggests the photoinduced absorption of the carrier in a few layers of two-dimensional perovskite. The negative signal suggests the bleaching and stimulated emission signal of perovskite in bulk. Hence, these changes from positive to negative signals indicate the energy transfer from a few layers to bulk. Fast decay components of stimulated emission were changed by changing the intensity of excitation pulses. To analyze the decay components of stimulated emission, global analysis was done for each time profile. Fig. shows the excitation intensity dependence of the lifetime of the stimulated emission. The initial lifetime component was related to the excitation light intensity by 1/N. These behaviors show the same dependence on excitation light intensity as the superfluorescence phenomena observed in time-resolved luminescence measurements[1]. We will discuss the spectrum evolution and relationship between energy transfer and superfluorescence at the conference site.
REFERENCES
[1] M. Biliroglu, K. Gundogdu et al., Nature photonics,
2022, 16, 324-329.
[2] T. Katayama, A. Furube et al., Jpn. J. Appl. Phys., 2023, 62(SG), SG1030.

Figure 1