RESUMO
We investigate coherent perfect absorption in layered thin-film structures with organic small molecules as absorbing material. We focus on strongly asymmetric resonator structures, realized with a high-optical-quality dielectric-distributed Bragg reflector and a thermally evaporated wedged organic layer on top. The optical properties of these devices are systematically investigated by selective optical pumping and probing of the structure along the wedge. We show that phases and amplitudes of all waves and their balance relations can be tuned such that coherent perfect absorption is achieved, i.e., almost all incident radiation is absorbed within the thin organic layer. We show that such wedged structures on highly reflective dielectric mirrors can be used as a novel approach to measure optical dispersion relations of absorbing materials in a broad spectral range without requiring any specific a priori knowledge of the absorbing film.
RESUMO
A comprehensive study of the optical properties of CsPbBr3 perovskite multiple quantum wells (MQW) with organic barrier layers is presented. Quantum confinement is observed by a blue-shift in absorption and emission spectra with decreasing well width and agrees well with simulations of the confinement energies. A large increase of emission intensity with thinner layers is observed, with a photoluminescence quantum yield up to 32 times higher than that of bulk layers. Amplified spontaneous emission (ASE) measurements show very low thresholds down to 7.3 µJ cm-2 for a perovskite thickness of 8.7 nm, significantly lower than previously observed for CsPbBr3 thin-films. With their increased photoluminescence efficiency and low ASE thresholds, MQW structures with CsPbBr3 are excellent candidates for high-efficiency perovskite-based LEDs and lasers.
RESUMO
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.