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Gold nanoclusters (AuNCs) are nanomaterials with interesting photoluminescent properties that can be endowed with biomolecular recognition and biocompatibility when stabilized with proteins. The interplay between the optical features of AuNCs and the function added by the protein makes them perfect candidates for generating hybrid protein‐inorganic nanomaterials. Focusing on protein stabilized‐AuNCs, hitherto most of the work has covered the use of natural proteins for in situ growth of AuNCs. However, the exploitation of design proteins for such endeavors enables fine‐tuning of the photoluminescent assets of AuNCs. In this work, rational protein engineering of modular protein scaffolds is applied for capping of non‐emissive, non‐passivated naked AuNCs, resulting in a fast and easy method for the synthesis of customizable and emissive protein‐AuNC nanomaterials. Tuning of the photoluminescent properties of the final hybrid module is obtained by appropriate choice of the coordination residues grafted on the same protein scaffold. The effects of ligands and coordination bonds are studied using time‐resolved photoluminescence and X‐ray absorbance spectroscopies, shedding light on the mechanisms behind the emerging properties of these hybrid materials. Moreover, the described versatile strategy opens new avenues for the synthesis of on‐demand photoluminescent hybrids for a wide spectrum of optical applications. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of a family of copper(I) complexes bearing a bridged bis-pyridyl ancillary ligand is reported, highlighting how the bridge nature impacts the photo- and electro-luminescent behaviours within the family. In particular, the phosphonium bridge led to copper(I) complexes featuring good electrochemical stability and high ionic conductivity, as well as a stark blue-to-orange luminescence shift compared to the others. This resulted in high performance light-emitting electrochemical cells reaching stabilities of 10 mJ at ca. 40 cd m−2 that are one order of magnitude higher than those of the other complexes. Overall, this work sheds light onto the crucial role of the bridge nature of the bis-pyridyl ancillary ligand on the photophysical features, film forming and, in turn, on the final device performances. [ABSTRACT FROM AUTHOR]

Amorphous thin films from solution‐processable semiconductors are key materials for low‐cost and large area optoelectronics. Design rules toward novel amorphous compounds with outstanding light emission and light amplification properties require understanding of the intimate relation between chemical and electronic structure. Here, a series of compounds with tunable electronic transition characters of the lowest excited state, from local excited (LE), hybrid local charge‐transfer (HLCT) to charge‐transfer (CT) character is delicately designed. By deploying a combination of computational calculations and femtosecond‐transient absorption experiments, it is shown that pure LE states strongly coupled to high wavenumber vibrational modes favor to form a few dominant discrete vibrational levels and are essential for optical gain, whereas HLCT or CT states are preferably coupled to low frequency vibrational modes and form a large number of consecutive vibrational levels which lead to broad excited‐state absorption overwhelming stimulated emission. The results provide guidelines for the rational design of efficient organic laser materials. [ABSTRACT FROM AUTHOR]

A fast and reversible switch between the neutral and protonated porphyrin forms inside a pliable porphyrinic metal–organic framework (MOF), enabled by reversible structural deformation is unveiled. This phenomenon is applied for the development of MOF‐polymer porous composites to reveal biogenic amines by color changes. [ABSTRACT FROM AUTHOR]

Simultaneous enhancement of photoluminescence quantum efficiency (PLQE) and optical gain in semiconducting polymer films is desirable for optically‐ or electrically‐pumped organic solid‐state lasers. In this work, a simple self‐dilution effect is achieved by introducing a small amount (≈10% by weight) of 2,5‐dimethyl‐1,4‐phenylene (DP) units in the backbone of poly(9,9‐dioctylfluorene) (PFO). The resulting copolymers, compared with PFO (PLQE 39%), exhibit a significantly increased PLQE (66%) while keeping similar absorption and photoluminescence profile, concomitant with an enhancement in optical gain properties. The radiative decay rate increases sharply along with a sustaining reduction in the non‐radiative decay rate in these copolymers, following similar principle of physical dilution of a luminescent compound in solution or in a polymer matrix. Among all the copolymers, the one containing 10% DP units exhibits the lowest amplified spontaneous emission/distributed feedback laser threshold (10.9 nJ/1.4 nJ, eightfold reduction), and the highest gain coefficient (54.4 cm−1). The results demonstrate that a moderate DP/fluorene ratio can maximize the beneficial self‐dilution effects. These investigations shed light on new design strategies to achieve conjugated polymers with concurrent high PLQE and large optical gain properties. [ABSTRACT FROM AUTHOR]

Thiophene‐based (Th‐based) derivatives have received wide attentions in organic optoelectronics due to their excellent and tuneable optoelectrical properties as well as chemical modification. However, the low photoluminescence quantum yield in solid state limits their application in solution‐processed light‐emitting optoelectronic devices, especially in organic lasers. Herein, a novel blue‐emitting steric Th‐based fluorophore (MC8‐Th) with excellent optical gain behavior for organic laser is reported. Interestingly, MC8‐Th neat film exhibits efficient exceptional deep‐blue amplified spontaneous emission (ASE) behavior with a remarkably low threshold of 6.0 µJ cm−2 and full‐width‐at‐half‐maximum value of 2.6 nm. Furthermore, random laser signals are also obtained with the lowest threshold of 4.1 µJ cm−2 when incorporating the compound into an inert polystyrene (PS) matrix. In addition, low threshold (16 µJ cm−2, fivefold lower than those of F8BT neat films) yellow–green ASE emission (560 nm) is achieved through Förster resonance energy transfer. Meanwhile, ultrafast transient absorption spectroscopy is deployed here to observe the single‐molecular excitonic behavior in solution and PS‐blend, intermolecular excited state in neat film, and efficient energy transfer in MC8‐Th:F8BT‐blend films. As far as known, MC8‐Th shows lower threshold ASE/lasing behavior for the Th‐based conjugated materials. [ABSTRACT FROM AUTHOR]

The effect of introducing side‐chain steric hindrance on the optoelectronic properties of the well‐studied green light emitting polymer (poly(9,9‐di‐n‐octylfluorene‐alt‐benzothiadiazole), F8BT) is investigated by means of replacing the 9,9‐dioctylfluorene unit by two novel steric hindrance functionalized monomers, namely, poly(9,9‐diarylfluorene‐alt‐benzothiadiazole) (FDFBT) and poly(9,9‐diarylfluorene‐4‐carbazole‐alt‐benzothiadiazole) (FCzBT). Bathochromic shifts of the optical spectra concomitant with enhanced photoluminescence quantum yields and improved film morphologies are found on the novel copolymers compared to F8BT. Femtosecond transient absorption spectroscopy demonstrates how steric hindrance effect in the novel copolymers manifests into enhanced stimulated emission and longer excited state lifetimes, associated with the suppression of polaron formation, all these being favorable features for light amplifying applications. Consequently, random lasing emission is achieved in films based on these copolymers with a threshold of three times lower than that of F8BT (22.95 µJ cm−2 for F8BT; 6.36 µJ cm−2 for FDFBT and 8.44 µJ cm−2 for FCzBT). Polymer light‐emitting diodes based on the novel copolymers exhibit performances comparable to the best reported on fluorene‐based devices. All of these results manifest the great potential of these novel copolymers for the application in the field of light‐emitting devices. [ABSTRACT FROM AUTHOR]

This study introduces a highly selective and sensitive luminescent sensor based on simply mixing a Tb(III)-based luminescent Metal–Organic Framework with polymethyl-methacrylate enabling to detect sub-ppb range of nitroaromatic vapours, properly. To the best of our knowledge, this is the first report on the use of this material for detecting gaseous analytes. Meanwhile, the present sensor dispels previous doubts about the selectivity and sensitivity of this material for the detection of nitroaromatic explosives in liquid media along with its applicability in the presence of potential interferences. [ABSTRACT FROM AUTHOR]

Organic–inorganic lead halide perovskites have emerged rapidly as the most attractive materials for photovoltaics in the last 10 years. Intense research has been done on crystal growth and morphology control to improve their power conversion efficiencies. Furthermore, perovskites also show great potential for optical amplification and lasing. Despite the numerous reports on how processing conditions affect the perovskite light-harvesting properties, effects on amplified spontaneous emission (ASE) or lasing performance have attracted considerably less attention. Herein, a detailed study on the ASE performance of methylammonium lead triiodide (MAPbI3) films, processed with lead acetate (Pb(Ac)2) as lead source following a one-step spin-coating method and exposed to different post-deposition conditions, is presented. It is found that the use of Pb(Ac)2 instead of lead iodide (PbI2) accelerates the crystal growth and simplifies the fabrication procedure. Even very thin MAPbI3 films (≈70 nm) can sufficiently support optical amplification and lasing in surface-emitting distributed-feedback (DFB) cavities. The facile and highly controllable MAPbI3 film formation observed with Pb(Ac)2 as precursor makes it a preferred choice with respect to PbI2 for future perovskite laser diodes. [ABSTRACT FROM AUTHOR]

Metal nanoclusters (NCs) are considered ideal nanomaterials for biological applications owing to their strong photoluminescence (PL), excellent photostability, and good biocompatibility. This study presents a simple and versatile strategy to design proteins, via incorporation of a di‐histidine cluster coordination site, for the sustainable synthesis and stabilization of metal NCs with different metal composition. The resulting protein‐stabilized metal NCs (Prot‐NCs) of gold, silver, and copper are highly photoluminescent and photostable, have a long shelf life, and are stable under physiological conditions. The biocompatibility of the clusters was demonstrated in cell cultures in which Prot‐NCs showed efficient cell internalization without affecting cell viability or losing luminescence. Moreover, the approach is translatable to other proteins to obtain Prot‐NCs for various biomedical applications such as cell imaging or labeling. [ABSTRACT FROM AUTHOR]

Metal nanoclusters (NCs) are considered ideal nanomaterials for biological applications owing to their strong photoluminescence (PL), excellent photostability, and good biocompatibility. This study presents a simple and versatile strategy to design proteins, via incorporation of a di‐histidine cluster coordination site, for the sustainable synthesis and stabilization of metal NCs with different metal composition. The resulting protein‐stabilized metal NCs (Prot‐NCs) of gold, silver, and copper are highly photoluminescent and photostable, have a long shelf life, and are stable under physiological conditions. The biocompatibility of the clusters was demonstrated in cell cultures in which Prot‐NCs showed efficient cell internalization without affecting cell viability or losing luminescence. Moreover, the approach is translatable to other proteins to obtain Prot‐NCs for various biomedical applications such as cell imaging or labeling. [ABSTRACT FROM AUTHOR]

Abstract: State‐of‐the‐art near‐infrared lasers based on poly[N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)] (PCDTBT) and poly(9,9‐dioctylfluorene‐alt‐benzothiadiazole) (F8BT) blends are reported. Polymer light‐emitting diodes (PLEDs) based on PCDTBT/F8BT blends with 30 wt% PCDTBT content exhibit a maximum radiance of 64.3 W sr−1 m−2 and external quantum efficiency of 2.11% with Commission Internationale de L'Eclairage (CIE) coordinates (x = 0.69, y = 0.30). Using an optimal blend ratio of 15 wt% PCDTBT in F8BT, a maximum gain value of 28.2 cm−1 at 710 nm is achieved, a remarkable value given that PCDTBT is a low emissive polymer extensively employed as donor polymer in organic photovoltaics. The lowest amplified spontaneous emission (ASE) and laser thresholds exhibited by the blends are 590 nJ pulse−1 (21 µJ cm−2) and 63.1 nJ pulse−1 (201 µJ cm−2). Transient absorption spectroscopy confirms efficient Förster resonant energy transfer from F8BT to PCDTBT which, together with the large miscibility of PCDTBT in F8BT, enables PCDTBT emission enhancement and optical gain. Furthermore, a ternary blend system composed of F8BT, PCDTBT, and poly(3‐hexylthiophene) is demonstrated, in which the ASE wavelength can be tuned in a 60 nm range from 650 to 710 nm at a very low threshold level via control of the blend content ratio. [ABSTRACT FROM AUTHOR]

Abstract: This paper reports state‐of‐the‐art fluorene‐based yellow‐green conjugated polymer blend gain media using Förster resonant‐energy‐transfer from novel blue‐emitting hosts to yield low threshold (≤7 kW cm−2) lasers operating between 540 and 590 nm. For poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) (15 wt%) blended with the newly synthesized 3,6‐bis(2,7‐di([1,1′‐biphenyl]‐4‐yl)‐9‐phenyl‐9H‐fluoren‐9‐yl)‐9‐octyl‐9H–carbazole (DBPhFCz) a highly desirable more than four times increase (relative to F8BT) in net optical gain to 90 cm−1 and 34 times reduction in amplified spontaneous emission threshold to 3 µJ cm−2 is achieved. Detailed transient absorption studies confirm effective exciton confinement with consequent diffusion‐limited polaron‐pair generation for DBPhFCz. This delays formation of host photoinduced absorption long enough to enable build‐up of the spectrally overlapped, guest optical gain, and resolves a longstanding issue for conjugated polymer photonics. The comprehensive study further establishes that limiting host conjugation length is a key factor therein, with 9,9‐dialkylfluorene trimers also suitable hosts for F8BT but not pentamers, heptamers, or polymers. It is additionally demonstrated that the host highest occupied and lowest unoccupied molecular orbitals can be tuned independently from the guest gain properties. This provides the tantalizing prospect of enhanced electron and hole injection and transport without endangering efficient optical gain; a scenario of great interest for electrically pumped amplifiers and lasers. [ABSTRACT FROM AUTHOR]

A novel technique for the creation of metal-organic framework (MOF) films based on soft-imprinting and their use as gas sensors was developed. The microporous MOF material [Zn2(bpdc) 2 (bpee)] (bpdc = 4,4'-biphenyldicarboxylate; bpee = 1,2-bipyridylethene) was synthesized solvothermally and activated by removing the occluded solvent molecules from its inner channels. MOF particles were characterized by powder X-ray diffraction and fluorescence spectroscopy, showing high crystallinity and intense photoluminescence. Scanning electron microscope images revealed that MOF crystals were mainly in the form of microneedles with a high surface-to-volume ratio, which together with the high porosity of the material enhances its interaction with gas molecules. MOF crystals were soft-imprinted into cellulose acetate (CA) films on quartz at different pressures. Atomic force microscope images of soft-imprinted films showed that MOF crystals were partially embedded into the CA. With this procedure, mechanically stable films were created, with crystals protruding from the CA surface and therefore available for incoming gas molecules. The sensing properties of the films were assessed by exposing them to saturated atmospheres of 2,4-dinitrotoluene, which resulted in a substantial quenching of the fluorescence after few seconds. The soft-imprinted MOF films on CA/quartz exhibit good sensing capabilities for the detection of nitroaromatics, which was attributed to the MOF sensitivity and to the novel and more efficient film processing method based on soft-imprinting. [ABSTRACT FROM AUTHOR]

ABSTRACT We study the correlation between Förster resonance energy transfer (FRET) and optical gain properties in conjugated polymer blends based on regioregular poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). First, FRET dynamics are investigated with femtosecond transient absorption spectroscopy observing a sub-picosecond energy transfer from F8BT to P3HT (550 fs) at medium doping levels (40% wt P3HT in F8BT). Amplified spontaneous emission (ASE) is then characterized in blends upon exciting predominantly the host and guest polymers, respectively. The corresponding density of absorbed photons at threshold conditions is compared upon host or guest photoexcitation as a method to quantitatively determine the FRET-assisted ASE efficiencies. We observe a reduction in ASE efficiency upon host photoexcitation of 20%, in the best case, respect to guest photoexcitation. Our results confirm that even in strongly coupled host:guest mixtures delayed exciton population by energy transfer is subtle to losses ascribed to exciton-exciton annihilation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2311-2317. [ABSTRACT FROM AUTHOR]

ABSTRACT Amongst the different optoelectronic applications of conjugated polymers, waveguide amplifiers and optically pumped lasers are those requiring larger photochemical stability, owing to the large irradiation conditions under operation. In this context, suitable waveguide optimization enabling the reduction of amplified spontaneous emission (ASE) threshold values appears as important as synthetic chemistry protocols to promote polymer robustness against photo-oxidation. In this work, we develop rib waveguides with different geometries based on four different fluorene-based compounds and assess the influence of rib confinement on ASE properties. We observe ASE threshold values as low as 8.9 × 10−4 mJ cm−2, being among the lowest threshold values reported so far on blue emitting polymer/oligomer waveguides. We demonstrate that the enhanced ASE efficiency on some of these rib waveguides leads to a fivefold increase in operation lifetime respect to spin-coated slab waveguides, thus confirming the impact of waveguide geometry on ASE operation stability. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1040-1045 [ABSTRACT FROM AUTHOR]

Conjugated luminescent polymers and oligomers, exhibiting stimulated emission (SE), are dispersed in polymethylmethacrylate (PMMA), films and optical fibers, either by blending or upon copolymerisation. With this PMMA doping, we aim to achieve gain and ultrafast optical switching. The modification of the dopant’s chemical structure allows the tuning of the SE spectral region. Furthermore, we aim to achieve dopant chain isolation while maximising their concentration. In this paper, we present an overview of the research done in this area in the context of the European Union (EU)-funded research project “plastic optical fibers with embedded active polymers for data communications-POLYCOM”. [ABSTRACT FROM AUTHOR]

The development of straightforward reproducible methods for the preparation of new photoluminescent coordination polymers (CPs) is an important goal in luminescence and chemical sensing fields. Isophthalic acid derivatives have been reported for a wide range of applications, and in addition to their relatively low cost, have encouraged its use in the preparation of novel lanthanide-based coordination polymers (LnCPs). Considering that the photoluminescent properties of these CPs are highly dependent on the existence of water molecules in the crystal structure, our research efforts are now focused on the preparation of CP with the lowest water content possible, while considering a green chemistry approach. One- and two-dimensional (1D and 2D) LnCPs were prepared from 5-aminoisophthalic acid and Sm3+/Tb3+ using hydrothermal and/or microwave-assisted synthesis. The unprecedented LnCPs were characterized by single-crystal X-ray diffraction (SCRXD), powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM), and their photoluminescence (PL) properties were studied in the solid state, at room temperature, using the CPs as powders and encapsulated in poly(methyl methacrylate (PMMA) films, envisaging the potential preparation of devices for sensing. The materials revealed interesting PL properties that depend on the dimensionality, metal ion, co-ligand used and water content. [ABSTRACT FROM AUTHOR]

Organic semiconductor micro/nanocrystals (OSMCs) have attracted great attention due to their numerous advantages such us free grain boundaries, minimal defects and traps, molecular diversity, low cost, flexibility and solution processability. Due to all these characteristics, they are strong candidates for the next generation of electronic and optoelectronic devices. In this review, we present a comprehensive overview of these OSMCs, discussing molecular packing, the methods to control crystallization and their applications to the area of organic solid-state lasers. Special emphasis is given to OSMC lasers which self-assemble into geometrically defined optical resonators owing to their attractive prospects for tuning/control of light emission properties through geometrical resonator design. The most recent developments together with novel strategies for light emission tuning and effective light extraction are presented. [ABSTRACT FROM AUTHOR]

We report on an organic photodiode configuration based on a donor/acceptor bilayer with opposed complementary thickness gradients. We rely on the strong dependence of the optical field on thickness to achieve spatially dependent spectral responses, a proof-of-concept for position sensitive detection. Ratiometric photocurrent values at two wavelengths allow for position determination independently of the light intensity with a spatial resolution below 600 μm. [ABSTRACT FROM AUTHOR]

The authors report on pump-probe measurements in a hybrid heterostructure consisting of a modified oligothiophene layer deposited over a GaAs substrate. Upon photoexcitation of the bilayer with 100 fs, a new photoinduced absorption band (PA2) appeared being attributed to oligothiophene cations arising from exciton diffusion and dissociation at the hybrid inorganic/organic interface. An exciton diffusion length in the organic layer of approximately 3.4 nm was estimated. [ABSTRACT FROM AUTHOR]

Precise control of exciton behavior is key in constructing high‐performance material systems for optoelectronic applications. Intrinsic sulfur in building aromatic units always results in strong aggregation, which causes exciton quenching, polaron formation, and enhanced nonradiative components. Herein, a series of solution‐processed thiophene‐based diarylfluorene derivatives is demonstrated and these fluorophores are encapsulated in the matrix system to suppress polaron formation for efficient green and red amplified spontaneous emission (ASE). A systematic photophysical study in solution, neat films, and polystyrene (PS)‐based encapsulated systems reveals that their emission behaviors are substantially promoted in PS encapsulated matrix due to the suppressed intermolecular aggregation. Furthermore, fs‐transient absorption (TA) measurements confirm that the encapsulated systems present stimulated emission (SE) and obtain the same intramolecular excited‐state character to those in solution, associated with the effective suppression of polaron formation and exciton quenched, in opposition to neat films with broad photoinduced absorption (PA) bands. Therefore, in contrast to the neat spin‐coated film without gain processing, these encapsulated systems give rise to notable optical gain properties with threshold values for green and red ASE as low as 70 μJ cm−2. Molecular encapsulation is an effective strategy to precisely enhance exciton behavior and emission efficiency for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Here we present the assembly of novel transparent all-polymer distributed feedback (DFB) lasers. Flexible and highly transparent cellulose diacetate (CdA) was employed as substrate on which gratings with different periods were engraved by thermal nanoimprinting with high fidelity. Highly luminescent conjugated polymers (CP), poly (9,9-dioctylfluorene) (PFO), poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), and a blend of F8BT and poly(3-hexylthiophene)-poly(9,9-dioctylfluorene-alt-benzothiadiazole) (P3HT:F8BT) were deposited by spin coating onto the nanostructured plastic surfaces, giving rise to perpendicular single-mode lasing emission in the blue, green, and red wavelength ranges, respectively. These lasers show linewidths below 1 nm and low thresholds (≈6 μJcm−2 for blue and red lasing emission), comparable to other state-of-the-art lasers obtained from similar optical gain materials on rigid substrates. The followed strategy is scalable and versatile, enabling the development of large area nanoimprinted DFB lasers (>1cm2) on plastic, which is highly relevant for applications in various markets. Multi-colored polymer lasers: Highly luminescent polymers can work as lasers when incorporated with suitable cavities and now the nano-imprinting makes the fabrication much cheaper and more scalable. An international team led by Prof Juan Cabanillas-Gonzalez from Madrid Institute for Advanced Studies in Nanoscience, Spain demonstrates transparent all-polymer distributed feedback (DFB) lasers in blue, green, yellow and red. The most important step is to make sub-wavelength periodic gratings on the flexible and highly transparent cellulose diacetate substrates by thermal nano-imprinting with high fidelity to maximize the constructive interference effect. As a result, these lasers show narrow linewidths below 1 nm at low power thresholds of several μJ cm^−2, which is comparable to conventional approaches. This large area nano-imprinting method is scalable and adaptable and it enables stackable multi-colored laser emission. [ABSTRACT FROM AUTHOR]

We report on an organic electroluminescent device with simplified geometry and emission in the red to near infrared (NIR) spectral region which, has the lowest turn-on voltage value, 2.3 V, among light emitting electrochemical cells (LEECs). We have synthesized and characterized three novel ruthenium π-extended phenanthroimidazoles which differ on their N^N ligands. The use of dimethyl electron donating groups along with the π-extended phenanthroimidazole moiety promotes ambipolar transport thereby avoiding the use of additional charge transport layers. Furthermore, a facile cathode deposition method based on transfer of a molten alloy (Ga:In) on top of the active layer is deployed, thus avoiding high vacuum thermal deposition which adds versatile assets to our approach. We combine ambipolar charge transport organic complex design and a simple ambient cathode deposition to achieve a potentially cost effective red to NIR emitting device with outstanding performance, opening new avenues towards the development of simplified light emitting sources through device optimization. [ABSTRACT FROM AUTHOR]

Electrically pumped organic lasing requires the integration of electrodes contact into the laser cavity in an organic light‐emitting diode (OLED) or organic field effect transistor configuration to enable charge injection. Efficient and balanced carrier injection requires in turn alignment of the energy levels of the organic active layers with the Fermi levels of the cathode and anode. This can be achieved through chemical substitution with specific aromatic functional groups, although paying the price for a substantial (and often detrimental) change in the emission and light amplifying properties of the organic gain medium. Here, using host–guest energy transfer mixtures with hosts bearing a systematic and gradual shift in molecular orbitals is proposed, which reduces the amplified spontaneous emission (ASE) threshold of the organic gain medium significantly while leaving the peak emission unaffected. By virtue of the low guest doping required for complete host‐to‐guest energy transfer, the injection levels in the blends are attributed to the host whereas the gain properties solely depend on the guest. It is demonstrated that the ASE peak and thresholds of blends with different hosts do not differ while the current efficiency of OLEDs devices is deeply influenced by molecular orbital tuning of the hosts. Energy level engineering is requested in future electrically pumped organic lasers. Chemical modification of active layer using functional substitution group such as fluorine atom may introduce unpredictable damage on emission or gain of the medium. Constructing efficient energy transfer system allows isolate tuning of electrical property of the hosts while the gain property of the guest remains undisturbed. [ABSTRACT FROM AUTHOR]

We demonstrated a simple, directly-readable approach for high resolution pH sensing. The method was based on sharp changes in Amplified Spontaneous Emission (ASE) of a Stilbene 420 (ST) laser dye triggered by the pH-dependent absorption of Bromocresol Green (BG). The ASE threshold of BG:ST solution mixtures exhibited a strong dependence on BG absorption, which was drastically changed by the variations of the pH of BG solution. As a result, ASE on-off or off-on was observed with different pH levels achieved by ammonia doping. By changing the concentration of the BG solution and the BG:ST blend ratio, this approach allowed to detect pH changes with a sensitivity down to 0.05 in the 10-11 pH range. [ABSTRACT FROM AUTHOR]