Phosphorescence Research Articles

Exploring the potential of phosphorescence for mitigating urban overheating: First time representation in an Urban Canopy Model

Phosphorescence (PP) has emerged as a promising passive cooling solution for the built environment, characterized by its ability to emit radiation persistently after photon absorption, thereby enhancing the solar radiation rejection capability and effective albedo of the surface. While various compounds have shown excellent properties for energy-saving purposes, assessing their benefits for the built environment towards their actual implementation still remains a challenge. To bridge the gap between laboratory-scale characterizations and real-world applications, this study employs the Princeton Urban Canopy Model (PUCM) to assess the surface cooling potential of PP coatings. This research represents the first numerical modeling of phosphorescence, extrapolating findings from experimentally validated parameters to conditions and scale of real cities. Results demonstrate the substantial capacity of PP to ameliorate surface overheating in urban areas, potentially reducing surface temperatures by up to −2.6 °C when optimized. Additionally, material optimization emerges as a crucial factor for exploiting the potential of phosphorescence in mitigating urban overheating, highlighting its strategic relevance for the urban canopy environment.

Photophysical analysis of dual fluorescence and phosphorescence emissions observed for semi-aliphatic polyimides at lower temperatures.

The photoluminescence (PL) properties of four types of blue fluorescent semi-aliphatic polyimides (PIs) derived from aromatic dianhydrides (ODPA, BPDA, HQDEA, and BPADA) and an alicyclic diamine (DCHM) were investigated at temperatures ranging from room temperature (RT, 298 K) to 30 K to analyse the origins of their non-radiative relaxation (NR) processes. These PIs exhibited significant increases in fluorescence (FL) intensity and lifetimes when lowering the temperature, stabilising below 100 K. The PIs containing ether (-O-) linkages showed a shoulder peak at around 500 nm below 150 K, which is attributable to phosphorescence (PH). These results show that the NR deactivation at RT includes three processes: intersystem crossing (ISC) from the excited singlet (S1) to the triplet (T1) state, temperature-dependent NR from the S1 state, which becomes suppressed below around 100 K, and temperature-independent NR. Based on the analyses of the temperature dependences, polymer structures, and quantum chemical analysis of molecular orbitals, we contemplate that the temperature-dependent NR is attributable to the excitation quenching by defect states mediated by excitation migration, and the temperature-independent NR may be caused by the deactivation of the excited state induced by molecular vibrations.

What is TADF (thermally activated delayed fluorescence) compared to the mechanisms of FL (fluorescence), PH (phosphorescence), and TTA (triplet–triplet annihilation) based on a novel naphthalimide sulfonylphenyl derivative as a host?

One of the biggest challenges in the field of optoelectronics is to easily identify the mechanisms involved in light-emitting materials. There are several different mechanisms of emission, and the best known are fluorescence (FL), phosphorescence (PH), thermally activated delayed fluorescence (TADF), and triplet–triplet annihilation (TTA). In this study, simple ways to diagnose these mechanisms are presented with an example. N,N-di(benzenesulfonylphenyl)-N-(N-2-aminomethylpyridine-1,8-naphthalimide)amine is synthesized as a host compound due to its high HOMO-LUMO and ionization potential (IP) values and three emitters consisting of 50 wt% Bis (1phenylisoquinoline))(acetylacetonate)iridium(III) (Ir(piq)2(acac)), 10-(4-(4,6-Diphenyl-1,3,5-triazin-2-yl)phenyl)-9,9-dimethyl-9,10-dihydroacridine (DMAC-TRZ) and 1,1′-(2,5-Dimethyl-1,4-phenylene)dipyrene (DMPPP) were considered. Overall, the host compound, doped Ir(piq)2(acac) and doped DMPPP follow the mechanisms of FL, the combination of FL and PH, and the combination of FL and TTA, as the photoluminescence (PL) decay life time and the PL intensity increased with decreasing temperature. However, DMAC-TRZ doped with the host compound showed the TADF mechanism, as the PL decay lifetime and the PL intensity increase simultaneously with increasing temperature. In addition, the difference between the singlet excited state (S1) and the triplet excited state T1 (ΔEST) from the PL and PH spectra at 77 K for the spin-coated DMAC-TRZ-doped host show the lowest value in between the samples at 0.02 eV, and the reverse intersystem crossing (rISC) effect is activated. Moreover, the linear slopes of the power dependence analysis of the DMPPP-doped host were calculated to be 2.04 and 0.91, indicating that there are two components (photons) for this sample which is strong evidence for the TTA mechanism. Taking into account the synthesized host compound, (Ir(piq)2(acac):host), (DMAC-TRZ:host) and (DMPPP:host) as emitter layers, the organic light emitting diodes (OLEDs) were fabricated via solution processing, and the TADF OLED exhibited the highest efficiency among the other OLEDs.

Novel Insight into the Photophysical Properties and 2D Supramolecular Organization of Poly(3,4-ethylenedioxythiophene)/Permodified Cyclodextrins Polyrotaxanes at the Air-Water Interface.

Two poly(3,4-ethylenedioxythiophene) polyrotaxanes (PEDOT∙TMe-βCD and PEDOT∙TMe-γCD) end-capped by pyrene (Py) were synthesized by oxidative polymerization of EDOT encapsulated into TMe-βCD or TMe-γCD cavities with iron (III) chloride (FeCl3) in water and chemically characterized. The effect of TMe-βCD or TMe-γCD encapsulation of PEDOT backbones on the molecular weight, thermal stability, and solubility were investigated in depth. UV-vis absorption, fluorescence (FL), phosphorescence (PH), quantum efficiencies, and lifetimes in water and acetonitrile were also explored, together with their surface morphology and electrical properties. Furthermore, dynamic light scattering was used to study the hydrodynamic diameter (DH) and z-potential (ZP-ζ) of the water soluble fractions of PEDOT∙TMe-βCD and PEDOT∙TMe-γCD. PEDOT∙TMe-βCD and PEDOT∙TMe-γCD exhibited a sharp monodisperse peak with a DH of 55 ± 15 nm and 122 ± 32 nm, respectively. The ZP-ζ value decreased from -31.23 mV for PEDOT∙TMe-βCD to -20.38 mV for PEDOT∙TMe-γCD, indicating that a negatively charged layer covers their surfaces. Surface pressure-area isotherms and Brewster angle microscopy (BAM) studies revealed the capability of the investigated compounds to organize into sizeable and homogeneous 2D supramolecular assemblies at the air-water interface. The control of the 2D monolayer organization through the thermodynamic parameters of PEDOT∙TMe-βCD and PEDOT∙TMe-γCD suggests potential for a wide range of optoelectronic applications.

Realization of Highly Efficient InP Quantum Dot Light‐Emitting Diodes through In‐Depth Investigation of Exciton‐Harvesting Layers

AbstractQuantum dot light‐emitting diodes (QLEDs) are considered promising candidates for several optoelectronic applications; however, they are plagued by the over‐injection of electrons compared to holes, which limits device efficiency. Studies have attempted to reuse the leaked electrons and transfer recombination energies via inserting an exciton‐harvesting layer (EHL) between the emissive layer (EML) and hole transport layer (HTL). This study conducts a detailed analysis of the energy transfer mechanisms to obtain better insights into improving the device performance. First, by analyzing the electroluminescence (EL) spectra and exciton dynamics, the effect of EHLs comprising phosphorescence (PH) or thermally activated delayed fluorescence (TADF) blue dopant is compared. Through parallel incorporation of those EHLs on QLEDs and organic LEDs, the minimal contribution of the PH‐EHL to energy transfer in QLEDs is confirmed, whereas the TADF‐EHL has a significant contribution. Second, highly efficient top‐emission green QLEDs with the TADF‐EHL are achieved. They exhibit a maximum luminance (L) and current efficiency (CE) of 40700 cd m−2 and 68.0 cd A−1, respectively, which are the highest among the reported values for green‐emitting InP QLEDs. The proposed approaches are expected to provide aid in the realization of highly efficient QLEDs from the analysis to the device optimization stage.

Alkali metal modified carbon nitride enhance photocatalytic performance for highly selective oxidation of benzyl C(sp3)-H bonds

Photocatalytic selective oxidation of C(sp3)-H bonds is an attractive strategy for synthesis of high value-added products due to the property of solar-driven and mild reaction conditions. However, improving photocatalytic activity and selectivity is still a grand challenge. Herein, we systematically compared the activity and selectivity for photocatalytic oxidation of 4-phenyltoluene by using the as-prepared photocatalysts. The results demonstrated that structure control and alkali metal modification could improve photocatalytic activity and selectivity by increasing the amount of singlet oxygen (1O2) molecules, which was proved by electron paramagnetic resonance (EPR) spectroscopy and phosphorescence (PH) spectroscopy. Moreover, no apparent decrease of conversion rate and selectivity during the 6 cycle runs indicated excellent stability of the prepared photocatalysts. This work revealed a basic mechanism on the energy transfer process of excitons and developed a feasible strategy for the design of C3N4-based photocatalysts.

Phosphine Oxide Linkage Manipulating Trinuclear Iridium(III) Complex for High‐Efficiency Bilayer Nondoped Organic Light‐Emitting Diodes

AbstractDeveloping high‐efficiency nondoped phosphorescence (PH) organic light‐emitting diodes (OLEDs) by solution processing is still a big challenge, due to high demand on quenching suppression ability of phosphors. Here, phosphine oxide (PO) linkage is incorporated between Ir3+ complexed cores of a trinuclear phosphorescent emitter named [Ir(PBI)2]3TPBIPO. The emission spectra of single‐molecular [Ir(PBI)2]3TPBIPO is identical to its mononuclear congeners, but its frontier molecular orbitals (FMO) and triplet state location are separated by electron‐withdrawing effect of P=O. Furthermore, by virtue of tetrahedral configuration of sp3‐hybrid PO linker, steric hindrance of [Ir(PBI)2]3TPBIPO is enhanced by locking the spatial orientations of the cores and vanishing packing freedom, giving rise to the effectively suppressed triplet quenching. As a consequence, neat [Ir(PBI)2]3TPBIPO film achieves a photoluminescence quantum yield of ≈90%, and a state‐of‐the‐art external quantum efficiency of 23.2% at 1000 nits from its spin‐coated bilayer non‐doped OLEDs.

Dealing with non-conventional LM-OSL curve shapes in quartz following bleaching; a deconvolution approach

In the linear modulation (LM) technique of optically stimulated luminescence (OSL), the stimulation power changes with a linear ramping rate, while the signal intensity starts to increase from background level and continues by forming peaks. In some cases as in the present study, the LM-OSL curve has a non-conventional shape with a strongly decaying signal at the beginning of the stimulation. In order to deal with this dominant decaying component, two different deconvolution approaches were used by adding to the initial part of the LM-OSL curves, besides the conventional LM-OSL components, (a) a phosphorescence (PH) decaying component and (b) a continuous wave (CW) - OSL decaying component . The fitting results showed that temperature dependences of the fitting parameters (τ and σ) contradict standard OSL theory, so the non-conventional dominant decay component is not another CW-OSL. This non-conventional component could be attributed to an intense optically stimulated phosphorescence (OSP) component, due to the experimentally verified stimulated temperature dependence of the decay coefficient λ. This signal is much more intense at stimulation temperatures 125 °C and below, with various arguments suggesting that at these temperatures the signal originates from the 110 °C TL trap.

White organic light emitting diodes based on localized surface plasmon resonance of Au nanoparticles and neat thermally activated delayed fluorescence and phosphorescence emission layers

White organic light emitting diodes (WOLEDs) incorporating gold (Au) nanoparticles (NPs) beneath PEDOT:PSS hole injection layer (HIL) and employing neat blue DMAC-DPS(B) and green 4CzIPN(G) thermally activated delayed fluorescence (TADF) emission layer (EML) together with sandwiched ultrathin red phosphorescence Ir(piq)2(acac)(R) EML have been fabricated and the effects of the localized surface plasmon resonance (LSPR) of Au NPs and EML thickness on the electroluminescence (EL) performance are investigated. It is found that EML thickness imposes vital influence on the EL performance of the WOLEDs and the WOLEDs with the embedded Au NPs and simple EML structure with optimal thickness of G(15 nm)/R(0.3 nm)/B(15 nm) demonstrate maximum power efficiency (PE), external quantum efficiency (EQE) and color rendering index (CRI) around 11.73 lm/w, 10.51% and 94, indicating the achievement of balance between EL efficiency and CRI by carefully adjustment of EML thickness with the presence of Au NPs. Furthermore, the LSPR effects from the Au NPs on the EL efficiency and CRI have been clearly demonstrated. Especially the green and red light emission is dramatically enhanced leading to enormous improvement of CRI, which can be ascribed to the remarkable enhancement of energy transferring inside G(15 nm)/R(0.3 nm)/B(15 nm) EML proved by the much shortened decaying lifetime at 475 and 550 nm from transient photoluminescence(PL) decaying testing. Almost double enhancement of the total fluorescence efficiency (including prompt fluorescence (PF) and delayed fluorescence (DF)) at 550 nm can be obtained with the assistance of LSPR from Au NPs, which increase from 23.85% to 49.82% and 15.22%–28.86% for respective EML of G(15 nm)/B(15 nm) and G(15 nm)/R(0.3 nm)/B(15 nm). The decaying dynamics including the DF, PF, phosphorescence (PH) and energy transferring inside G(15 nm)/R(0.3 nm)/B(15 nm) EML with and without embedded Au NPs is discussed in details. The study provides an easy way to utilize the LSPR of Au NPs together with simple neat TADF and phosphorescent EML to develop high quality WOLEDs.

Excited-state engineering of universal ambipolar hosts for highly efficient blue phosphorescence and thermally activated delayed fluorescence organic light-emitting diodes

The development of high-performance universal host materials for both blue electrophosphorescence and thermally activated delayed fluorescence (TADF) is one of the main challenges for organic light-emitting diode (OLED) technology. In this work, based on four quaternary ambipolar hosts with insulated donor-acceptor (D-A) structures, the influence of the excited-state characteristics for these hosts on their device performance was systematically investigated. It was showed that on the premise of the similar electrical properties and excited-state energy levels for positive host-dopant energy transfer (ET), the weak exciton capture ability, embodied as low exciton binding energy (Eb), for the hosts could facilitate the Dexter ET to the dopant through charge migration. Since the charge-transfer -featured excited states and small Eb of blue TADF emitters, in contrast to the blue phosphorescence (PH) counterparts, the influence of the host Eb on the device efficiencies of blue TADF dyes was dramatically enlarged, reflecting the higher sensitivity of the latter to host characteristics. In consequence, 9CzFDBFDPO with the smallest Eb endowed its blue TADF and PH devices with the state-of-the-art performance, e.g. EQE beyond 20% and EQE roll-off within 20% at 500 cd m−2. This work showed that based on the systematically optimized excited-state characteristics, the ambipolar hosts can be competent in both high-efficiency blue PH and TADF OLEDs, which is crucial for their commercial applications.

Uncertainty analysis in Structured Laser Illumination Planar Imaging (SLIPI) applied to non-linear signals: gas-phase phosphor thermometry

Recent studies have used structured laser illumination planar imaging (SLIPI) combined with phosphor thermography to remove multiple scatter effects and near-wall reflections, which lead to biases in temperature measurements and reduced spatial resolution. We show that for the typical non-linear pump-signal range under which thermographic phosphors are used, errors may arise in the reconstruction of the temperature field using SLIPI. In this study, synthetic laser induced phosphorescence (LIP) images are generated numerically by adapting the Synthetic PIV Image Generator (SIG) for the purpose. The simulations are combined with phosphorescent signal yield functions obtained from experimental data to investigate the application of SLIPI to gas-phase phosphor thermography. We conclude that whilst SLIPI is effective in removing scattering noise for phosphors for which the two-colour signal ratio is insensitive to the laser fluence, it creates a bias in the temperature measurement otherwise. We also show that the extent of multiple scatter in LIP images is always overestimated by SLIPI, owning to the non-linear emission behaviour and particle image diffraction.

Recent progress of phosphine electroluminescent materials and devices

Organic light emitting diodes (OLEDs) have been attracting much attention and have been studied extensively by scientists and engineers in both academic and industrial communities, due to their great advantages of self-emitting, fast response, wide view-angle, full color capacity, high efficiency, low power consumption, ultra-thinness, lightness and flexibility for the applications of new generation flat panel displays and solid-state lighting sources. With the full use of active-matrix OLED (AMOLED) screen in iPhone X, OLED technology has become the mainstream information display technology and has gained more than 40% of market share. In the era of information, liquid crystal display technology will be gradually replaced by OLED technology. However, OLEDs technology still faces many challenges, including low yield, high cost, short service life, environmentally unfriendly and so on, which urgently requires more in-depth and detailed research in material development and device design. Since the first OLED reported by CW Tang, OLED technology has developed from the first generation of fluorescence (FL) technology, the second generation of phosphorescence (PH) technology to the third generation of thermally activated delayed fluorescence (TADF) technology. In general, PH materials are heavy metal complexes, in which triplet excited state is the main radiative excited state. Since singlet exciton can translate into triplet exciton through intersystem crossing (ISC) process, therefore, in theory, 100% electrogenerated excitons can be used in phosphorescence materials. Compared with the first generation of fluorescence materials, which can only use 25% single state electrogenerated excitons, the electro-optic conversion efficiency is greatly improved in phosphorescence materials. However, heavy metal ions in PH materials not only increase the cost, but also bring some potential environmental pollution. TADF technology can realize the transformation of non-radiative triplet excitons into radiative singlet excitons through reverse ISC (RISC) process, and thus achieving 100% exciton utilization. TADF material is usually pure organic molecule based on a push-pull electron system, thus making up for the defects of phosphorescent material. Therefore, as a kind of molecular electroluminescent devices, innovation of material system is the foundation for the development of OLED technology. With the insulating effect, moderate electronic effect, large steric hindrance, multi-functionalizability and coordination effect, aryl phosphine (oxide) group is one of the few groups with multiple functions. Through comprehensively utilizing these functions, aryl phosphine (oxide) group reveal the unique advantage in selectively optimizing molecular optoelectronic properties, further realizing high-efficiency OLED, and providing a platform for selective investigation of the influence of single property variation on optoelectronic performance. Recently, phosphine optoelectronic materials have been gradually developed as one of the focuses in OLED field, whose excellent performance and clear structure-property relationship reveal the significant theoretical and application values regarding to enriching OLED material, suggesting the methods in material design and optimization and promoting the OLED technology innovation. Based on material design strategy, we developed phosphine host materials, emitters and electron transporting materials and deeply investigated the photophysical properties, excited-state characteristics, electrical properties and OLED performance. In this paper, the main works are summarized, with the expectation to provide reference for the subsequent study on phosphine optoelectronic materials.

Efficient blue phosphorescent organic light emitting diodes based on exciplex and ultrathin Firpic sandwiched layer

Abstract The high efficient blue phosphorescent organic light emitting diodes (PHOLEDs) employing ultrathin Firpic layer sandwiched between electron donor mCP and electron acceptor TmPyPB layers were fabricated, and the dependence of the electroluminescence (EL) performance on the ultrathin Firpic layer thickness were investigated. It was found that the Firpic layer thickness imposed vital influence on the OLEDs EL efficiency and the one with the 0.3 nm Firpic demonstrated the optimal power efficiency (PE) of 50 lm/w and the external quantum efficiency (EQE) close to 18%. The sandwiched ultrathin Firpic layer would not impede the formation of the exciplex between mCP and TmPyPB, and the balance between the exciplex formation and exciplex decaying showed strong dependence on Firpic layer thickness and imposed vital influence on the energy transfer, fluorescence and phosphorescence inside the emissive layer. There were three radiative decaying processes involved, i.e. the prompt and delayed fluorescence (PF and DF) of the exciplex as well as the phosphorescence (PH) of the Firpic, and the final EL relied on the competition of those processes. The optimal EL performance might be attributed to the combining benefits of the balanced PF, DF and PH decaying, alleviated Dexter-transfer-based triplet-triplet annihilation (TTA) and the triplets diffusion suppressed architecture.

Synthesis and optoelectronic properties of an electrically stimulated phosphorescent iridium complex

In order to better describe and verify the mechanism of electrophosphor discoloration, an ionic iridium complex with different counterions is designed and synthesized. It is found that the luminescent properties of the phosphor not only show the concentration and acid / base induced phosphorescence, but also show the phosphorescence change induced by electrical stimulation. The hydrogen bond acceptor (-NH) is introduced into the ionic iridium complex to modulate the emission wavelength of the complex by different counterions. In order to further control the emission wavelength of the complexes, a series of ionic iridium complexes with different counterions are designed and synthesized by selecting the auxiliary ligands containing two hydrogen bond acceptors (-NH). It is proved that there is not only electrostatic interaction between the cations and counterions, but also interesting hydrogen bonds. In addition, because the hydrogen bond strength formed by complex anions and different counter anions is different, it can effectively control the photophysical properties of complexes and adjust the emission wavelength from 493 nm to 591 nm. In conclusion, the phosphorescence change induced by electric field can be realized by applying the electric field to change the hydrogen bonding intensity. At the same time, the construction of quasi solid-state information storage devices is beneficial to the development of phosphorescent materials in information optoelectronic devices.

P‐182: Universal Host o‐DiCbzBz for High Efficiency Phosphorescence and Thermal Active Delayed Fluorescence Organic Light Emitting Device

A bipolar compound, o‐DiCbzBz, was synthesized conjugating two hole transporting moieties carbazole (Cbz) with an electron transporting moiety benzimidazole (Bz). Employing as a universal host doped with red, green, blue phosphorescence (PH) and thermal active delayed fluorescence (TADF) emitter to be the emitter layer inside organic light emitting diodes, devices exhibited an excellent efficiency performance, especially an excellent external quantum efficiency (ηEQE) of 31.8% with PH FIrpic and a high ηEQE of 26.3% with TADF 4CzIPN

What are Fluorescence and Phosphorescence?

What are Fluorescence and Phosphorescence?

Room-Temperature Phosphorescence of Crystalline Metal-Free Organoboron Complex.

The photoluminescence (PL) properties of a metal-free organoboron complex, bis(4-iodobenzoyl)methanatoboron difluoride (1BF2 ), were elucidated. At room temperature, 1BF2 emits blue fluorescence (FL) in nBuCl upon photoexcitation. In contrast, crystals of 1BF2 emit green PL comprised of FL and phosphorescence (PH). The room-temperature PH of crystalline 1BF2 is a consequence of 1) suppression of thermal deactivation of the S1 and T1 excited states and 2) enhancement of intersystem crossing (ISC) from the S1 to T2 or T1 . The results of X-ray crystallographic and theoretical studies supported the proposal that the former (1) is a result of intermolecular interactions caused by π-stacking in the rigid crystal packing structure of 1BF2 . The latter (2) is an effect of not only the heavy-atom effect of iodine, but also the continuous π-stacking alignment of 1BF2 molecules in crystals, which leads to a forbidden S1 →S0 transition and a small energy gap between the S1 and T2 or T1 .

Fluorescence and phosphorescence: Easier to investigate than to spell

First Page

Balanced Dual Emissions from Tridentate Phosphine-Coordinate Copper(I) Complexes toward Highly Efficient Yellow OLEDs.

Dual emissive copper(I) halide complexes TTPPCuX (X = Cl, Br, I) with a triphosphine ligand and stable tetrahedral geometries are constructed, in which TTPPCuI successfully achieves the balanced dual thermally activated delayed fluorescence and phosphorescence (PH) emissions with PH fraction of 39% at ambient temperature, supporting the equal triplet exciton reallocation for the state-of-the-art device performance.

Luminescence Properties of Eu 2+ -activated CaO-MgO-SiO 2 Long-lasting Phosphorescence Glasses

Luminescence Properties of Eu 2+ -activated CaO-MgO-SiO 2 Long-lasting Phosphorescence Glasses