Spontaneous Radiation Amplification in a Microsphere‐Coupled CsPbBr₃ Perovskite Vertical Structure

Abstract

Microsphere (MS) cavities hold great potential in nanophotonics due to their extraordinary optical properties. All‐inorganic trihalide perovskites with high environmental stability and easy‐for‐preparation have shown great promise for the next‐generation optoelectronic nanodevices. Unfortunately, the nonradiative recombination of exciton is inevitably aggravating the photoluminescence quantum yields (PLQYs). Here, a microsphere‐coupled CsPbBr3 perovskite vertical structure is proposed for amplification of spontaneous radiation (SR) up to 190‐fold. The mechanisms of SR amplification by an MS cavity are completely revealed, for the first time, including Mie focusing (MF) for energy harvesting, directional antenna (DA) for emission convergence, and whispering‐gallery modes (WGMs) for regulation of exciton dynamics. The temperature‐dependent photoluminescence (PL) spectra clarify the contributions of WGMs for the boosting of SR decay and suppression of exciton–phonon interactions for giant PL enhancement. Furthermore, a straightforward approach is presented for a selective MS array capped on a perovskite microcrystal (PeMC) film as a vertical structure for patterned PL enhancement. The excitation‐power‐ and excitation‐observation‐angle‐dependent luminescence contrast inspire a novel anticounterfeiting strategy. The vertical architecture not only advances the understanding of microcavity‐based SR amplification from PeMCs, but also offers opportunities to facilitate the synergistic manipulation of optical fields and exciton–phonon interactions for developing high‐efficient optoelectronic devices.

Microsphere Photonic Superlens for a Highly Emissive Flexible Upconversion-Nanoparticle-Embedded Film

“…It has been acknowledged that the nanofocusing via the MPS generated a small excitation light spot at the shadow side of the microsphere. 47 The corresponding evaluated power densities are shown in the top x-axis of Figure 2ed,. The initial values of n lower than 1 in Figure 2e indicated the high population at the intermediate states owing to the increased excitation intensity via MPS nanofocusing.…”

“…The MPS can also regulate the luminescence emission due to the directional antenna effect. 47 According to eq 2, ERI D values were individually estimated to be 87@365 nm, 80@450 nm, 66@475 nm, and 42@645 nm, via the objective with NA = 0.25 (±14.5°). The effect of the spacing between the MPS and the UCNPembedded film on ERI D was also numerically calculated, where the reduction of ERI D was negligible for the spacing smaller than 1500 nm.…”

“…Meanwhile, the phonon-induced nonradiative transitions can be suppressed by the resonant modes. 47 Figure 4c shows the numerical simulation of WGMs supported by the MPS with various spacing layer thicknesses (t). The maximum Q factor was achieved when t = 0, i.e., the MPS was in contact with the UCNP-embedded film, for the substantial interaction strength between resonant photons with UCNPs via evanescent waves.…”

“…39 Moreover, the microsphere is a typical microcavity with the simplest symmetric geometry supporting optical whispering-gallery modes (WGMs) with an ultrahigh Q factor up to 10 8 , strengthening the interaction between trapped photons and nanoparticles/molecules/ions amplifying nonlinear phenomena. 40 These superior properties, i.e., Mie-resonant nanofocusing, the directional antenna effect, and high-Q WGMs, endow microspheres with promising novel applications in nanophotonics, e.g., subdiffraction-limited nanopatterning, 41 super-resolution imaging, 42 nanoparticle transduction, 43 nanomanipulation, 44 optical frequency comb generation, 45 ultralow-threshold lasing, 46 fluorescence enhancement, 47 and ultrasensitive Raman detection. 48 The fiber-coupled single microsphere was reported as a microlens for upconversion fluorescence biodetection with an ERI up to 2 orders of magnitude.…”

“…, Mie-resonant nanofocusing, the directional antenna effect, and high- Q WGMs, endow microspheres with promising novel applications in nanophotonics, e.g. , subdiffraction-limited nanopatterning, super-resolution imaging, nanoparticle transduction, nanomanipulation, optical frequency comb generation, ultralow-threshold lasing, fluorescence enhancement, and ultrasensitive Raman detection . The fiber-coupled single microsphere was reported as a microlens for upconversion fluorescence biodetection with an ERI up to 2 orders of magnitude .…”