Search Results (80)

High-performance full-color displays and white lighting require stable and efficient red, green, and blue emitters; however, they are often limited by wide bandgaps, imbalanced carrier injection/transport, complex device structures, and high material costs. To address these challenges, we designed and synthesized a multifunctional deep-blue molecule (PPI-F-PO) integrating a phenanthroimidazole moiety, a 9,9-diphenylfluorene unit, and a phosphine oxide group. The twisted structure of fluorene, featuring a sp³-hybridized carbon, effectively suppresses conjugation extension and aggregation-caused quenching, whereas the electron-withdrawing phosphine oxide group enhances electron transport. Consequently, it exhibits good thermal stability, high solid-state photoluminescence quantum yield (58.8%), and high triplet energy (E_T = 2.54 eV). Non-doped blue OLEDs based on this emitter achieve a maximum external quantum efficiency (EQE) of 2.52% with deep-blue CIE coordinates of (0.16, 0.06). Moreover, using this material as a host, green and orange-red phosphorescent OLEDs exhibit maximum EQEs of 15.4% and 9.7%, respectively, along with low efficiency roll-off. This work demonstrates that a bipolar deep-blue emitter with high triplet energy can act both as a high-efficiency standalone emitter and as a universal host for lower-energy phosphors, thereby simplifying device architecture and reducing material costs for full-color OLEDs. Full article

Using advanced optical modelling, we quantify how sinusoidal corrugation and emitter dipole orientation jointly govern light extraction from OLED thin-film stacks into a glass substrate for red, green, and blue emission. Irrespective of emission colour, the corrugation aspect ratio (AR = height/period) is the dominant geometric parameter controlling extraction, with absolute period and height playing secondary roles, as periods of 600–1000 nm deliver similar gains across all colours. Extraction peaks at AR ≈ 0.2 for predominantly horizontal dipoles, AR ≈ 0.5 for vertical dipoles, and AR ≈ 0.3 for isotropic orientations. For the isotropic case, extraction improves by up to 40%, 34%, and 20% relative to flat red, green, and blue devices, respectively. Absorption analysis attributes the principal gains to suppression of surface-plasmon-polariton losses of vertical dipoles, supported by local dipole reorientation, waveguide disruption, and scattering. Because practical texturing can alter dipole orientation, optimum conditions must be re-evaluated; if orientations follow the sinusoidal profile, an AR of approximately 0.2–0.3 is favoured for isotropic to moderately horizontal orientations, whereas higher ARs benefit strongly vertical orientations. The results provide guidelines for co-optimising corrugation geometry and dipole orientation for high-efficiency OLEDs. Full article

Organic optoelectronic devices receive appreciable attention due to their low cost, ecology, mechanical flexibility, band-gap engineering, brightness, and solution process ability over a broad area. In this study, we designed and studied organic light-emitting diodes (OLEDs) consisting of an assembly of natural dyes, extracted from noble fir leaves (evergreen) and blue hydrangea flowers mixed with poly-methyl methacrylate (PMMA) as light emitters. We experimentally demonstrate the effective conversion of blue light emitted by an inorganic laser/photodiode into longer-wavelength red and green tunable photoluminescence due to the excitation of natural dye–PMMA nanostructures. UV-visible absorption and photoluminescence spectroscopy, ellipsometry, and Fourier transform infrared methods, together with optical microscopy, were performed for confirming and characterizing the properties of light-emitting diodes based on natural dyes. We highlighted the optical and physical properties of two different natural dyes and demonstrated how such characteristics can be exploited to make efficient LED devices. A strong pure red emission with a narrow full-width at half maximum (FWHM) of 23 nm in the noble fir dye–PMMA layer and a green emission with a FWHM of 45 nm in blue hydrangea dye–PMMA layer were observed. It was revealed that adding monolayer MoS₂ to the nanostructures can significantly enhance the photoluminescence of the natural dye due to a strong correlation between the emission bands of the inorganic–organic emitters and back mirror reflection of the excitation blue light from the monolayer. Based on the investigation of two natural dyes, we demonstrated viable pathways for scalable manufacturing of efficient hybrid OLEDs consisting of assembly of natural-dye polymers through low-cost, purely ecological, and convenient processes. Full article

We report the first observation of room-temperature phosphorescence (RTP) of quinine sulfate (QS) in poly (vinyl alcohol) (PVA) films. Steady-state and time-gated measurements were performed to characterize the phosphorescence spectra, anisotropies, and lifetimes to estimate the phosphorescence properties. The RTP response of organic emitters in polymer matrices is particularly sensitive to ambient humidity and oxygen levels. Hence, to assess the environmental stability of the system, QS-doped PVA films were cast from a single batch and divided into paired specimens, one of which was encapsulated with a pressure-sensitive laminate, while the other one was left non-laminated. Over 14 days under ambient laboratory conditions, the absorbance and fluorescence of both films remained unchanged, whereas the exhibited phosphorescence diverged significantly. The unlaminated film exhibited a progressive loss of afterglow intensity, a noticeable red shift in the phosphorescence spectrum, and a pronounced shortening of the phosphorescence lifetime, while the laminated film retained its initial RTP intensity, spectral profile, and lifetime throughout the entire experiment. Full article

Minimizing the spectrum overlaps of energy transfer (ET) is necessary but not sufficient for achieving high-sensitivity film thermosensing. Herein we have designed two blue emitters of DBA-BPAc and Z-DBABH exhibiting blue and bluish-green emissions, respectively, to hybridize with the red-emitting Ir(MDQ)₂(acac). Compared with Z-DBABH, DBA-BPAc shows a larger spectrum overlap of ET and a relatively smaller discrepancy in fluorescence thermal decay, while its emission spectrum displays a much smaller overlap with that of Ir(MDQ)₂(acac). The dual minimization of spectrum overlap of ET and emissions results in its superior ratiometric film thermosensing of the DBA-BPAc film in wide-range and high-temperature regions. The DBA-BPAc/Ir(MDQ)₂(acac) film exhibits a maximum relative sensitivity (S_r) of 3.36% °C⁻¹ at 166 °C, exceeding 0.43% °C⁻¹ in 50–265 °C. In comparison, the Z-DBABH/Ir(MDQ)₂(acac) system displays a reliable but relatively lower performance, with a maximum S_r of 1.92% °C⁻¹ (at 300 °C). The temperature resolution remains below 2.06 °C throughout the entire temperature range (20–300 °C), achieving a best value of 0.60 °C at 180 °C. Notably, both films display distinct naked-eye color transitions with temperature changes, enabling multi-level anti-counterfeiting applications. This work provides new insights for designing high-performance thermometers. Full article

Mn⁴⁺-activated fluoride phosphors possess outstanding luminescent properties, making them highly suitable for applications in lighting and display technologies. However, the synthesis of such phosphors generally requires the use of large amounts of highly toxic aqueous HF, leading to serious environmental pollution. To eliminate the use of hazardous HF solution, a low-temperature molten salt method employing NH₄HF₂ was developed to synthesize the narrow-band red emitter Cs₂GeF₆: Mn⁴⁺ phosphor. Following the reaction, the product was washed with a dilute H₂O₂ solution to remove residual NH₄HF₂ and other impurities. The phase purity and morphology were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, and the luminescence properties were examined via photoluminescence (PL) spectroscopy. The obtained phosphors exhibit bright red emission characteristics of Mn⁴⁺ under blue-violet excitation. Among them, Cs₂GeF₆: 0.08 Mn⁴⁺ shows the highest emission intensity, with an internal quantum efficiency (IQE) of 78%. A white light-emitting diode (WLED) fabricated by combining this phosphor with a blue chip and commercial Y₃Al₅O₁₂: Ce³⁺ (YAG) phosphor achieved a high luminous efficacy (LE) of ~146 lm/W, a correlated color temperature (CCT) of ~4396 K, and a color rendering index (Ra) of ~83, alongside excellent operational color stability. Full article

Cycloplatinated complexes incorporating pyrene chromophores of the formulae (C^C*)Pt(acac) (3, 4), (C^C* = Pyrenyl-NHC, acac = acetylacetonate) were prepared and fully characterized. For comparison, two regioisomeric complexes were prepared following synthetic procedures developed by us. One isomer has the Pt(II) center attached to the 2-position of the pyrene chromophore, while the other regioisomer has the metal center attached at the 1-position of the organic chromophore. The molecular structures of 3 and 4 were ascertained by X-ray diffraction, and they prove the identity of the targeted compounds. Both complexes are emissive at room temperature in the red part of the spectrum in poly(methyl methacrylate) (PMMA), as well as at 77 K in 2-methyltetrahydrofuran (2-MeTHF). The regioisomer containing the Pt(II) at the 1-position shows enhanced emissive properties compared to the other regioisomer. Full article

Advances in OLED display technology have increased the demand for high-performance luminescent materials, yet efficient red emitters with narrow emission spectra remain rare. Here, two new polycyclic compounds (O-QA and S-QA) are designed by incorporating oxygen/sulfur into a carbonyl/nitrogen skeleton. Photophysical and theoretical studies reveal their hybridized local and charge-transfer state characteristics. In toluene, O-QA and S-QA show photoluminescence peaks at 586/579 nm with narrow emission spectra, while doped films exhibit strong red emissions peaking at 598/600 nm with high PL quantum yields of 67%/60%. The OLEDs using these emitters achieve red electroluminescence (EL) peaks at 598/602 nm, and attain maximum external quantum efficiencies of 7.36%/14.54%. This work may provide guidance for the development of narrow-spectrum red emitters based on carbonyl/nitrogen frameworks. Full article

Herein, we study a method for developing a broad-emission emitter that can emit radiation from the visible light to NIR regions. Firstly, an NIR phosphor’s optical properties (e.g., scattering vs. weight concentration, conversion efficiency, and emission spectra under blue and red light excitation) are investigated. Then, pcW-LEDs encapsulated with NIR down-conversion phosphor samples are prepared to test these optical properties. The results show that pcW-LEDs encapsulated with the NIR phosphor at different weight concentrations of 10.0%, 12.5%, and 15.5%, respectively, emit a broadband emission from 400 nm to 900 nm. The EQE values of the pcW-LEDs encapsulated with NIR phosphor at weight concentrations of 10%, 12.5%, and 15.0% are 26%, 23%, and 19%, respectively. The correlated color temperatures of these samples are 5767 K, 5940 K, and 6068 K, respectively. The obtained radiant fluxes of the samples are 26 mW, 22 mW, and 18 mW, respectively, at an injection current of 50 mA. Full article

In this thesis, a 650 nm dense spectral beam combining (DSBC) system based on a compression telescope module (CM) and an imaging module (IM) is proposed (CM&IM DSBC system). Based on twenty-two (22) 650 nm COS (Chip on Submount) single-emitters, the system successfully achieves the first high-power and non-crosstalk beam combining output in the visible red band, with a maximum beam output power of 29.984 W. Compared with the 650 nm traditional DSBC system we proposed last year, the system solves both the crosstalk problem due to its larger optical path and the beam combining power drop caused by the direct reduction in the optical path. The final output power and DSBC efficiency are improved by more than 53% and 10%, respectively. The final beam brightness is improved by nearly 30%. Compared to a COS single-emitter, the brightness increase is more than 22 times. This achievement provides a new idea for the subsequent experimental research and product development of higher-power visible red-light band DSBC systems that can be applied in the industrial field. Full article

Blue exciplexes, a critical innovative component in organic light-emitting diodes (OLEDs) technology, exhibit substantial potential for enhancing device efficiency, reducing driving voltage, and simplifying structural designs. This article reviews the pivotal role of blue exciplexes in OLEDs, analyzing their unique advantages and challenges as emitters and host materials. Through optimized molecular design, blue exciplexes achieve high color purity and emission efficiency, surpassing conventional fluorescent materials. Additionally, their wide energy bands and high triplet energy provide opportunities to improve the performance of sky-blue, deep-blue, and white OLEDs. However, limitations in deep-blue efficiency, material degradation due to high-energy excitons, and spectral red-shift pose significant challenges to their development. This review offers a comprehensive perspective and research reference on the photophysical mechanisms of blue exciplexes and their applications in display and lighting fields. Full article

Life cycle assessment (LCA) is a reference methodology to evaluate environmental impacts along supply chains of products. Planetary boundaries (PBs) were developed to define the safe operating space (SOS) for humanity. So far, no study has investigated whether wine production and consumption result in crossing the planetary boundary of climate change and no SOS has been calculated for wine production in Greece. Our study applies an LCA according to the European Product footprint environmental category rules to calculate the climate change score of a bottle of 0.75 L of Greek red organic wine in 2021 and 2026, and also applies planetary boundaries to investigate whether the climate change boundary is exceeded. The latter employed the calculation of a SOS based on four partitioning methods: grandfathering principle, economic value, agricultural land area use, and calorific content. The LCA results showed that wine is a carbon emitter. The 2021, 2026-Low yield, and 2026-High yield systems resulted in positive climate change scores between 0.69–1.14 kg CO₂ eq.bottle wine⁻¹. The PBs revealed that carbon emissions of wine production in 2021 exceeded all four SOSs, while carbon emissions of expected wine production in 2026 remained within the SOS of grandfathering, economic value and agricultural land area use partitionings, but exceeded the SOS of the caloric content partitioning. The PB method can be complementary to LCA results in terms of providing context to decision-makers in business and public policy on whether red organic wine production and consumption remain within ecological constraints on human development. Full article

Density functional theory (DFT) calculations were employed to study a series of complexes of general formula [Ru(salen)(X)(CO)]^0/−1 (X = Cl⁻, F⁻, SCN⁻, DMSO, Phosphabenzene, Phosphole, TPH, CN⁻, N₃⁻, NO₃⁻, CNH⁻, NHC, P(OH)₃, PF₃, PH₃). The effect of ligands X on the Ru-CO bond was quantified by the trans-philicity, Δσ¹³C NMR parameter. The potential of Δσ¹³C to be used as a probe of the CO photodissociation by Ru(II) transition metal complexes is established upon comparing it with other trans-effect parameters. An excellent linear correlation is found between the energy barrier for the Ru-CO photodissociation and the Δσ¹³C parameter, paving the way for studying photoCORMs with the ¹³C NMR method. The strongest trans-effect on the Ru-CO bond in the [Ru(salen)(X)(CO)]^0/−1 complexes are found when X = CNH⁻, NHC, and P(OH)₃, while the weakest for X = Cl⁻, NO₃⁻ and DMSO trans-axial ligands. The Ru-CO bonding properties were scrutinized using Natural Bond Orbital (NBO), Natural Energy Decomposition Analysis (NEDA) and Natural Orbital of Chemical Valence (NOCV) methods. The nature of the Ru-CO bond is composite, i.e., electrostatic, covalent and charge transfer. Both donation and backdonation between CO ligand and Ru metal centre equally stabilize the Ru(II) complexes. Ru-CO photodissociation proceeds via a ³MC triplet excited state, exhibiting a conical intersection with the T₁ ³MLCT excited state. Calculations show that these complexes show bands within visible while they are expected to be red emitters. Therefore, the [Ru(salen)(X)(CO)]^0/−1 complexes under study could potentially be used for dual action, photoCORMs and theranostics compounds. Full article

Organic light-emitting diodes (OLEDs) based on phosphorescent materials are among the most promising technologies for displays and lightings. For red-emitting heteroleptic iridium complexes (HICs), vast and major research has been focused on the design and synthesis of cyclometalated ligands, while relatively little attention has been given to ancillary ligands which also play important roles in manipulating the optoelectronic and electroluminescent properties of HICs. Seven deep red-emitting HICs were designed and synthesized by systematically modifying the alkyl groups in β-diketone-type ancillary ligands. These HICs exhibited similar physical and optoelectronic properties, with OLED devices based on these materials achieving consistent emission peaks at 624 nm and CIE coordinates of (0.68, 0.32). Among the synthesized HICs, Ir(dmippiq)₂(dmeacac), featuring 3,7-dimethyl-4,6-nonanedione as the ancillary ligand, demonstrated the best OLED performance, achieving a champion external quantum efficiency (EQE) of 18.26%. This result highlights that engineering the alkyl groups in β-diketone ancillary ligands can significantly enhance device performance. Full article

Organic light-emitting diodes (OLEDs) have emerged as one of the dominant technologies in displays due to their high emission efficiency and low power consumption. However, the development of blue color emitters has fallen behind that of red and green emitters, posing challenges in achieving optimal efficiency, stability, and accessibility. In this context, thermally activated delayed fluorescence (TADF) emitters hold promise as a potential solution for cost-effective, exceptionally efficient, and stable blue OLEDs due to their potential high efficiency and stability. TADF is a principle where certain organic materials can efficiently convert both singlet and triplet excitons, theoretically achieving up to 100% internal quantum efficiency. This research focused on diphenyl sulfone derivatives with carbazole groups as TADF compounds. Quantum chemical calculations and photoluminescence properties show the potential TADF properties of the molecules. New materials exhibit glass transition temperatures that would classify them as molecular glasses. Depending on the structure of the molecule, the photoluminescence emission is in the blue or green spectral region. Organic light-emitting diodes were fabricated from neat thin films of emitters by the wet casting method. The best performance in the deep blue emission region was achieved by a device with a turn-on voltage of 4 V and a maximum brightness of 178 cd/m². In the blue-green emission region, the best performance was observed by an OLED with a turn-on voltage of 3.5 V, reaching a maximum brightness of 660 cd/m². Full article