The success of metal halide perovskites in photovoltaic and light-emitting diodes (LEDs) motivates their application as a solid-state thin-film laser. Various perovskites have shown optically pumped stimulated emission of lasing and amplified spontaneous emission (ASE), yet the ultimate goal of electrically pumped stimulated emission has not been achieved. As an essential step toward this goal, here, a perovskite diode structure that simultaneously exhibits stable operation at high current density (≈1 kA cm −2 ) and optically excited ASE (with a threshold of 180 μJ cm −2 ) is reported. This diode structure achieves an electroluminescence quantum efficiency of 0.8% at 850 A cm −2 , which is estimated to be ≈3% of the charge carrier population required to reach ASE in the same device. It is shown that the formation of a large angle waveguide mode and the reduction of parasitic absorption losses are two major design principles for diodes to obtain a positive gain for stimulated emission. In addition to its prospect as a perovskite laser, a new application of electrically pumped ASE is proposed as an ideal perovskite LED architecture allowing 100% external radiation efficiency.

for various fields of application, such as chemical material analysis, characterization of light sources, or calibration of monochromators and laser sources. Established techniques for realizing wavelength-selective light detection use one of two primary approaches: first, wavelength separation by an auxiliary structure, [1] i.e., a filter array or grating, where narrow light bands are directed onto individual pixels of a photodetector (PD) (array) with a broadband response; second, wavelength separation by the photoactive part itself, achieved by a multilayer arrangement of detectors, where every single detector is sensitive to a specific wavelength band. [2,3] Such spectroscopic devices commonly comprise solid hardware components that restrict them from versatile integration.Recent developments, however, demonstrate both the huge drive and great potential in terms of easy-to-integrate, low-cost, or lightweight applications, [4] e.g., narrowband photodiodes, [5][6][7] voltage-tunable Fabry-Pérot micro-interferometers, [8] or broadband sensors requiring wavelength multiplexing. [9] A smart approach to significantly reduce the device complexity was presented by Gautam et al. [10] A single-pixel and single-layer device was used to achieve a wavelength-sensitive photocurrent response that can discriminate red, green, and blue (RGB) values via the polarization of a polymer film in an aqueous surrounding. Only recently, a system was presented that consists of a multilayer single pixel of graded-bandgap perovskites evoking a wavelength-sensitive photocurrent response. [11] Here, we present a single-chip wavelength sensor that exploits the dynamics of singlet and triplet states to discriminate a certain input signal. We employ a solution-processed host-guest system comprising organic room-temperature phosphors and fluorescent colloidal quantum dots (QDs), thereby introducing a new, promising application for organic room-temperature phosphorescence (RTP). The latter has been put to multifaceted use, [12] such as programmable luminescent tags, [13] oxygen sensing, [14] or moisture sensing. [15] Owing to their unique scalable optical properties, high quantum yield, and elevated photostability, colloidal quantum dots proved themselves valuable in a myriad of applications, like light-emitting diodes (LEDs), [16,17] solar cells, [18][19][20] or transistors. [21,22] Here, we present a single-layer approach that turns wavelength information into a distinct photocurrent response with a spectral resolution down to 1 nm and below while covering a wavelength range from 300 to 410 nm.Wavelength-discriminating systems typically consist of heavy benchtop-based instruments, comprising diffractive optics, moving parts, and adjacent detectors. For simple wavelength measurements, such as lab-on-chip light source calibration or laser wavelength tracking, which do not require polychromatic analysis and cannot handle bulky spectroscopy instruments, lightweight, easyto-process, and flexible single-pixel devices are attracting increasing atten...

Currently, organic phosphorescent particles are heavily used in sensing and imaging. Up to now, most of these particles contain poisonous and/or expensive metal complexes. Environmentally friendly systems are therefore highly desired. A purely amorphous system consisting of poly­(methyl methacrylate) particles with incorporated N,N,N′,N′-tetrakis­(4-carboxyphenyl)­benzidine emitter molecules is presented in this work. Single particles with sizes between 400 and 840 nm showdepending on the environmentbright fluorescence and phosphorescence. The latter is observed when oxygen is not in the proximity of the emitting dye molecules. These particles can scavenge singlet oxygen, which is produced during the photoexcitation process, by incorporating it into the polymer matrix. This renders their use to be unharmful for the surrounding matter with possible application in marking schemes for living bodies.

The development of organic materials displaying room-temperature phosphorescence is a research field that has attracted more and more attention in the last years. Most studies focus on designing or optimizing emitter molecules to increase the phosphorescent performance in host:emitter systems. Rarely, the overall thin-film preparation routines are compared with respect to their triplet-state luminescence yield. Herein, different film preparation techniques are investigated using the very same emitter molecule. A variation of host polymer, post-annealing temperature, and fabrication procedure is evaluated with respect to the obtained phosphorescent lifetime, photoluminescent quantum yield, and phosphorescence-to-luminescence ratio. This study elaborates the importance of different film preparation techniques and gathers a concise set of data which is helpful to anyone optimizing the phosphorescence of a particular system.