Accurate monitoring of UV radiation is critical across numerous disciplines, yet bridging the gap between complex electronic devices and ambiguous, gradual colorimetric indicators remains challenging. Addressing this challenge, a novel approach for a customizable, purely organic UV threshold dosimeter based on oxygen-mediated room-temperature phosphorescence (RTP) is presented. The active layer comprises a purely organic emitter (BP-2TA) dispersed in a poly(methyl methacrylate) (PMMA) host, protected by a polyvinyl alcohol layer. Upon UV irradiation, photochemical oxygen consumption yields a high-contrast, sharp turn-on of the emitter's phosphorescent emission once a specific cumulative UV dose is reached. This activation depends strictly on the cumulative dose rather than irradiation intensity and is systematically tunable by adjusting the emitter concentration. A comprehensive physical model is introduced that describes the wavelength and thickness dependencies, revealing a thin-film regime where the activation dose becomes independent of the active layer thickness. Supported by shelf-life stability tests, these findings, alongside the proposed operational modes, establish the RTP-based sensors as robust UV dosimeters that could be easily integrated into production processes.

Purely organic room-temperature phosphorescence (RTP) emitters are key components of programmable luminescent tags (PLTs), photonic devices for rewritable information storage and UV dosimetry. In this work, we systematically explore the design space of donor-acceptor and donor-acceptor-donor organic phosphorescent emitters in symmetric and asymmetric architectures. Phenoxathiine (PX) is introduced as an alternative donor to thianthrene (TA), combined with benzophenone (BP) or pyridine (Py) as acceptors. Through photophysical characterization, quantum chemical simulations, and PLT device testing, we identify structure-property relationships and, in particular, investigate the impact of the individual moieties on the emission properties and stability. The RTP emission wavelength is primarily tunable through the donor moiety: PX-based emitters emit sky-blue (λ_P = 480 nm), while TA-based emitters emit in the green (λ_P = 520 nm) due to an increased Stokes shift. The acceptor unit strongly influences the phosphorescence quantum yield, with Py-based emitters systematically outperforming BP-based ones. All newly synthesized PX-containing emitters show sufficient performance in PLT devices, though with reduced photostability compared to TA-based counterparts. Together, these results demonstrate that systematic donor-acceptor design enables predictable control over RTP emission properties, advancing the rational development of high-performance RTP-based photonic devices.

Organic semiconductors provide the potential of biodegradable technologies, but prototypes do only rarely exist. Transparent, ultrathin programmable luminescent tags (PLTs) are presented for minimalistic yet efficient information storage that are fully made from biodegradable or at least industrially compostable, ready-to-use materials (bioPLTs). As natural emitters, the quinoline alkaloids show sufficient room temperature phosphorescence when being embedded in polymer matrices with cinchonine exhibiting superior performance. Polylactic acid provides a solution for both the matrix material and the flexible substrate. Room temperature phosphorescence can be locally controlled by the oxygen concentration in the film by using Exceval as additional oxygen blocking layers. These bioPLTs exhibit all function-defining characteristics also found in their regular nonenvironmentally degradable analogs and, additionally, provide a simplified, high-contrast readout under continuous-wave illumination as a consequence of the unique luminescence properties of the natural emitter cinchonine. Limitations for flexible devices arise from limited thermal stability of the polylactic acid foil used as substrate allowing only for one writing cycle and preventing an annealing step during fabrication. Few-cycle reprogramming is possible when using the architecture of the bioPLTs on regular quartz substrates. This work realizes the versatile platform of PLTs with less harmful materials offering more sustainable use in future.

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8–1.5) × 10 –7 cm 2 /s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

We present a design for programmable luminescent tags fully made from biodegradable, ready-to-use materials (bioPLTs) allowing for waste-free information storage. Quinine embedded in polylactic acid as host material provides sufficient room temperature phosphorescence (RTP) for easy readout even under continuous-wave illumination. Exceval is used as oxygen blocking layer to locally control the oxygen-sensitive RTP emission for high-resolution writing of information. Accordingly, these bioPLTs exhibit all function-defining characteristics also found in their regular non-biodegradable analogs even including a flexible design when using polylactic acid foils as substrate.

Conventional organic optoelectronic devices suffer from low carrier mobility limited by the static and dynamic disorder. Organic crystals with long-range order can circumvent the effects of disorder and significantly improve the charge transport. While highly ordered organic crystals offer the desirable electronic coupling strength and charge transport, their integration into large-area optoelectronic devices remains a challenge. Here, monolithic integrated triclinic crystal rubrene light-emitting diodes (LEDs) are presented using epitaxial growth with functional additives being engineered into the films. Superior charge transport, excellent operational and long-term stability in these light-emitting devices are demonstrated. By comparing two rubrene-based LEDs, one made from amorphous and one from crystalline rubrene layers, their exciton dynamics are estimated using comprehensive transient electroluminescence simulation. The crystalline LEDs show high triplet-triplet annihilation (TTA) rate constant similar to TTA rate constant of triclinic single crystals determined by optical spectroscopy. At the same time, the crystalline phase enhances drastically the singlet-fission and bimolecular annihilation rates, which reduces the overall performance of the LED compared to its amorphous counterpart. Finally, an outlook on the potential applications of rubrene and/or its derivatives crystalline films are provided for enhancing the performance of organic and hybrid optoelectronic devices.

Semiconducting polymers enable the fabrication of low-cost, large-area electronic devices by using low-temperature solution-processing methodologies on flexible substrates. This work presents three novel host materials for the emitting layer (EML) of organic light-emitting diodes (OLEDs). Efficient hosts should possess a number of properties, such as high triplet energy, good and balanced charge-carrier transport, suitable frontier orbital levels that match those of the neighboring layers, and morphological stability. To this end, carbazole-based polymers featuring the electron-withdrawing group (EWG) phenylphosphine oxide at different positions of the chain were designed and synthesized by Suzuki coupling. Chemical and optical characterizations of the polymers were performed prior to the charge -transport property analysis through the fabrication of single-carrier devices. Finally, these materials were incorporated into a green OLED architecture as solution processed EML where tris(2-phenylpyridine)iridium(III) (Ir(ppy)(3)) acts as phosphorescent emitter dopant.

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.

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, easy-to-process, and flexible single-pixel devices are attracting increasing attention. Here, a device is proposed for monotonously transforming wavelength information into the time domain with room-temperature phosphorescence at the heart of its functionality, which demonstrates a resolution down to 1 nm and below. It is solution-processed from a single host-guest system comprising organic room-temperature phosphors and colloidal quantum dots. The share of excited triplet states within the photoluminescent layer is dependent on the excitation wavelength and determines the afterglow intensity of the film, which is tracked by a simple photodetector. Finally, an all-organic thin-film wavelength sensor and two applications are demonstrated where this novel measurement concept successfully replaces a full spectrometer.

Most materials recently developed for room temperature phosphorescence (RTP) lack in practical relevance due to their inconvenient crystalline morphology. Using amorphous material systems instead, programmable luminescent tags (PLTs) based on organic biluminescent emitter molecules with easy processing and smooth sample shapes are presented recently. Here, the effective quenching of the emitter's RTP by molecular oxygen (O2 ) and the consumption of the excited singlet O2 through a chemical reaction represent the central features. With customized activation schemes, high-resolution content can be written and later erased multiple times into such films, providing a versatile yet simple photonic platform for information storage. However, two important limitations remain: The immutable fluorescence of the emitters outshines the phosphorescent patterns by roughly one order of magnitude, allowing readout of the PLTs only after the excitation source is turned off. The programming of these systems is a rather slow process, where lowest reported activation times are still >8 s. Here, a material-focused approach to PLTs with fast activation times of 120 ± 20 ms and high-contrast under continuous-wave illumination is demonstrated, leading to accelerated programming on industry relevant time scales and a simplified readout process both by eye and low cost cameras.

Recently, we reported programmable luminescent tags (PLTs) based on organic biluminescent emitter molecules. Here, the effective quenching of the emitters room temperature phosphorescence (RTP) by molecular oxygen (O2) and the consumption of the excited singlet O2 through a chemical reaction represent the central features of the PLTs. By incorporating a semipermeable oxygen barrier layer, different illumination schemes allow to toggle between high and low oxygen concentration and, consequently, no RTP and RTP in the transparent layer. With customized activation schemes, high resolution content can be written and later erased multiple times into such films, providing a versatile yet simple photonic platform for information storage and exchange. However, two important limitations remain: (i) The immutable fluorescence of the biluminescent emitters outshines the phosphorescent patterns by roughly one order of magnitude, allowing read-out of the PLTs only after the excitation source is turned off. (ii) The programming of these systems is a rather slow process, where lowest reported activation times are still greater than 8 s. Here, we demonstrate PLTs based on an optimized organic RTP emitter with fast activation times of 119 ms and high-contrast under continuous-wave (cw) illumination, leading to accelerated programming on industry relevant time scales and a simplified readout process both by eye and low cost cameras.

By utilizing the room temperature phosphorescence (RTP) of organic materials, transparent and flexible optical tags with high resolutions up to 700 dpi are realized. Through masked ultraviolet (UV) illumination or laser ray writing, any phosphorescent pattern can be printed into the transparent device. With the help of infrared (IR) light, it is possible to fully erase the imprint again. This cycle is shown to be repeatable at least 40 times. The functional layer of these devices consists of different organic biluminescent emitters doped into a polymethylmethacrylate (PMMA) host matrix covered with an oxygen barrier layer. However, due to the sample preparation in ambient conditions, molecular oxygen is still present in the emissive layer. This leads to a full quenching of the phosphorescence and the generation of excited singlet oxygen due to triplet-triplet interactions involving the oxygen triplet groundstate. The singlet oxygen has a high chemical reactivity and thus is able to form a bond with the surrounding materials. Consequently, the molecular oxygen concentration decreases in the illuminated areas. The concurrently decreasing oxygen-quenching rate is at some point outcompeted by the radiative rate of the emitter, enabling locally resolved phosphorescence. This emission resembles the intended pattern. The oxygen permeability of the barrier layer is temperature dependent and increases with rising temperature, which can be realized using a hotplate or IR illumination. This enables an oxygen refilling of the functional layer and therefore increases the quenching rate to a value prior to the activation process, leading to the vanishing of the phosphorescent image. After a short cooling phase, new information can be printed into the device. In continuous wave illumination, fluorescence may limit the contrast between activated areas and those still containing oxygen. Hence, different material systems showing reduced fluorescence without losing the oxygen quenching ability of the phosphorescence, are developed and tested.

Measuring the photoluminescence quantum yield (PLQY) is a method often used within numerous fields of luminescent material science. Determining its absolute value relies on counting photons and hence, it is a very sensitive technique. Therefore, systematic errors that may occur during the measurement are discussed widely. However, the statistical uncertainty within those measurements remains mainly unconsidered. Here, we propose a new way of data analyses that exploits multiple measurements and a subsequent evaluation using the weighted mean. This leads in an efficient way to a very low statistical uncertainty. Additionally, time-dependent influences on the measurement can be identified that way.

In recent years, there has been a growing interest in purely organic materials showing ultralong room-temperature phosphorescence with lifetimes in the range of seconds. Still, the longest known phosphorescence lifetimes are only achieved with crystalline systems so far. Here, a rational design of a completely new family of halogen-free organic luminescent derivatives in amorphous matrices, displaying both conventional fluorescence and phosphorescence is reported. Hydrogen bonding between the newly developed emitters and an ethylene-vinyl alcohol copolymer (Exceval) matrix, which efficiently suppresses vibrational dissipation, enables bright long-lived phosphorescence with lifetimes up to 2.6 s at around 480 nm. The importance of the chosen matrix is shown as well as the implementation in an organic programmable luminescent tag.

Organic room temperature phosphorescence (RTP) is used to realize rewriteable (>40 cycles), transparent and flexible optical tags with high resolution (>700 dpi). The devices contain an organic biluminescent emitter doped into polymethylmethacrylate (PMMA). They show phosphorescence, which in general is quenched by molecular oxygen. However, by illuminating with ultraviolet light (365 nm), this molecular oxygen locally vanishes at the irradiated area, enabling RTP at defined spots. Further, by illuminating with infrared light, the system can be refilled with oxygen leading to quenching of the RTP again. Therefore, any luminescent pattern can be written into and erased from the tag using light only.

The large majority of materials recently developed for room temperature phosphorescence (RTP) lacks of practical relevance due to their inconvenient crystalline morphology and hence their limited sample shapes. A much more promising, but yet to be explored strategy for novel photonic devices is RTP from amorphous material systems. Recently, we reported programmable luminescent tags (PLTs) based on organic biluminescent emitter molecules with easy processing and smooth sample shapes. Here, the effective quenching of the emitters amorphous RTP by molecular oxygen (O2) and the consumption of the excited singlet O2 through a chemical reaction represent the central features of the PLTs. With customized activation schemes, high resolution content can be written and later erased multiple times into such films, providing a versatile yet simple photonic platform for information storage and exchange. However, two important limitations remain: (i) The immutable fluorescence of the biluminescent emitters outshines the phosphorescent patterns by roughly one order of magnitude, allowing read-out of the PLTs only after the excitation source is turned off. (ii) The programming of these systems is a rather slow process, where lowest reported activation times are still greater 8 s. Here, we demonstrate a material-focused approach to realize PLTs with fast activation times of 120 ms and high contrast under continuous-wave (cw) illumination, leading to accelerated programming on industry relevant time scales and a simplified readout process both by eye and low-cost cameras.

Biluminescent organic emitters show simultaneous fluorescence and phosphorescence at room temperature. So far, the optimization of the room-temperature phosphorescence in these materials has drawn the attention of research. However, the continuous-wave operation of these emitters will consequently turn them into systems with vastly imbalanced singlet and triplet populations, which is due to the respective excited-state lifetimes. This study reports on the exciton dynamics of the biluminophore NPB (N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1-biphenyl)-4,4-diamine). In the extreme case, the singlet and triplet exciton lifetimes stretch from 3 ns to 300 ms, respectively. Through sample engineering and oxygen quenching experiments, the triplet exciton density can be controlled over several orders of magnitude, allowing us to study exciton interactions between singlet and triplet manifolds. The results show that singlet-triplet annihilation reduces the overall biluminescence efficiency already at moderate excitation levels. Additionally, the presented system represents an illustrative role model to study excitonic effects in organic materials.