Photoluminescence Quantum Yield Research Articles

Extended Surface Bands Enabled Lasing Emission and Wavelength Switch from Sulfur Quantum Dots.

The development of a lasing wavelength switch, particularly from a single inorganic gain material, is challenging but highly demanded for advanced photonics. Nonetheless, all current lasing emission of inorganic gain materials arises from band-edge states, and the inherent fixed bandgap limitation of the band-edge system leads to the inaccessibility of lasing wavelength switching from a single inorganic gain material. Here the realization of a single inorganic gain material-based lasing wavelength switch is reported by proposing an alternative lasing emission strategy, that is, lasing emission from surface gain. Previous efforts to achieve surface-gain-enabled lasing emission have been hindered by the limited gain volume provided by surface states due to the broad emission bandwidth and/or low emission efficiency. This challenge is overcome by introducing extended surface bands onto the surface of sulfur quantum dots. The extended surface bands contribute to a high photoluminescence quantum yield and narrow emission bandwidth, thereby providing sufficient gain volume and facilitating stimulated emission. When combined with whispering gallery mode microcavity, surface gain enabled lasing emission manifests an ultralow threshold of 8.3 µJcm-2. Remarkably, the reconfigurable perturbation to surface gain, facilitated by molecular affinity, allows for the realization of the lasing wavelength switch from a single inorganic gain material.

Toward an Ideal Light Source for Indoor Photosynthesis: Broadband Red Emission in Zero-Dimensional Hafnium-Based Metal Halide (TPP)2HfCl6·4C2H3N:Sb3.

With suitable electron-phonon coupling strength, a near-unity broadband photoluminescence quantum yield (PLQY) can be achieved in organic-inorganic hybrid metal halides (OIHMHs) via self-trapped exciton (STE) emission. However, it is still challenging to obtain high-quality red emission from OIHMHs with a desirable emission wavelength and high chemical stability, which hinders their practical application in high-performance displays, plant-growth lighting, and biomedical imaging. Herein, a series of hafnium-based zero-dimensional (TPP)2HfCl6·4C2H3N (TPP: tetraphenylphosphonium) single crystals with different Sb3+ doping levels are synthesized. The Sb3+-doped (TPP)2HfCl6·4C2H3N shows dual-band red emission with a full width at half-maximum of 178 nm and a high PLQY of 91.09%. This broad dual-band emission originates from dopant-induced extrinsic free excitons and STEs. Furthermore, (TPP)2HfCl6·4C2H3N:Sb3+ was employed as a luminescence converter in a light-emitting diode (LED) for plant growth regulation. A correlated color temperature of 4055 K and a color rendering index of 82.13 were achieved upon excitation of the LED at 365 nm. These results provide fundamental perspectives on the emission behavior of Sb3+-doped OIHMHs and illustrate their promise for use in plant-growth lighting.

Enhancing Optical Properties of Zn-Mn Solid Solution Hybrid Halides for Wide Color Gamut Backlight Displays.

Hybrid metal halides display a range of optical properties and hold promise for various applications such as solid-state lighting, anti-counterfeiting measures, backlight displays, and X-ray detection. The incorporation of zinc into (C13H26N)2MnBr4 aims to enhance its structural rigidity and improve its narrow band green light emission properties. The resulting (C13H26N)2ZnBr4 compound exhibits an identical crystal structure to (C13H26N)2MnBr4, indicating the potential for a solid solution of varying Zn and Mn ratios within this structural framework. (C13H26N)2Zn0.2Mn0.8Br4 exhibits significantly enhanced properties, including a photoluminescence quantum yield of 92%, a minimum full width at half maximum of 43nm, and 85% retention of room temperature emission at 420K. Additionally, crystals of (C13H26N)2ZnCl4 and (C7H18N)2ZnX4 (X = Br, I) are synthesized, with (C7H18N)2ZnBr4 displaying luminescent color changes dependent on excitation. (C7H18N)2Zn0.2Mn0.8Br4 demonstrates reversible phase transitions and alterations in optical properties. A white light-emitting diode utilizing (C13H26N)2Zn0.2Mn0.8Br4 and commercial phosphors exhibited a color gamut of 112.2% of the National Television Standards Committee 1931 Standard. This investigation introduces a stable and highly efficient narrow-band green phosphor suitable for displays.

Enhancing Spin-Orbit Coupling in an Indolocarbazole Multiresonance Emitter by a Sulfur-Containing Peripheral Substituent for a Fast Reverse Intersystem Crossing.

A fast reverse intersystem crossing (RISC) remains an ongoing pursuit for multiresonance (MR) emitters but faces formidable challenges, particularly for indolocarbazole (ICz) derived ones. Here, heavy-atom effect is introduced first to construct ICz-MR emitter using a sulfur-containing substitute, simultaneously enhancing both spin-orbit and spin-vibronic coupling to afford a fast RISC with a rate of 1.2×105s-1, nearly one order of magnitude higher than previous maximum values. The emitter also exhibits an extremely narrow deep-blue emission peaking at 456nm with full-width at half-maxima of merely 12nm and a photoluminescence quantum yield of 92%. Benefiting from its efficient triplet upconversion capability, this emitter achieves not only a high maximum external quantum efficiency (EQE) of 31.1% in organic light-emitting diodes but also greatly alleviates efficiency roll-off, affording record-high EQEs of 29.9% at 1000cdm-2 and 18.7% at 5000cdm-2 among devices with ICz-MR emitters.

Synergistic Intramolecular Non-Covalent Interactions Enable Robust Pure-Blue TADF Emitters.

Stability-issues of organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) require further advancements, especially in pure-blue range of CIEy < 0.20, existing a dilemma between color purity and device lifetime. Though improving bond-dissociation-energy (BDE) can effectively improve material intrinsic stability, strategies to simultaneously improve BDE and photophysical performances are still lacking. Herein, it is disclosed that synergistic intramolecular non-covalent interactions (Intra-NI) can achieve not only the highest C─N BDE among blue TADF materials, but enhanced molecular-rigidity, near-unity photoluminescent quantum yields and short delayed lifetime. Pure-blue TADF-OLEDs based on proof-of-concept TADF material realize high external-quantum-efficiency and record-high LT80@500cdm-2 of 109h with CIEy = 0.16. Furthermore, deep-blue TADF-sensitized devices exhibit high LT80@500cdm-2 of 81h with CIEy = 0.10. The findings provide new insight into the critical role of Intra-NI in OLED materials and open the way to tackling vexing stability issues for developing robust pure-blue organic emitters and other functional materials.

Indirect-to-direct bandgap transition in GaP semiconductors through quantum shell formation on ZnS nanocrystals

Although GaP, a III-V compound semiconductor, has been extensively utilized in the optoelectronic industry for decades as a traditional material, the inherent indirect bandgap nature of GaP limits its efficiency. Here, we demonstrate an indirect-to-direct bandgap transition of GaP through the formation of quantum shells on the surface of ZnS nanocrystals. The ZnS/GaP quantum shell with a reverse-type I heterojunction, consisting of a monolayer-thin GaP shell grown atop a ZnS core, exhibits a record-high photoluminescence quantum yield of 45.4% in the violet emission range (wavelength = 409 nm), validating its direct bandgap nature. Density functional theory calculations further reveal that ZnS nanocrystals, as the growth platform for GaP quantum shells, play a crucial role in the direct bandgap formation through hybridization of electronic states with GaP. These findings suggest potential for achieving direct bandgaps in compounds that are constrained by their inherent indirect energy gaps, offering a strategy for tailoring energy structures to significantly improve efficiencies in optoelectronics and photovoltaics.

High‐Efficiency Circularly Polarized Luminescence Regulation of a Dye‐Doped Polymer Film by Acid/Aggregation

AbstractSmart materials with circularly polarized luminescence (CPL) tunable ability show great potential for advanced information storage and encryption. While an effective integration of high photoluminescence quantum yield (PLQY) and facile regulation of CPL property in thin films are of great significance, it is challenging due to the scarcity of suitable materials and complexity of systems. Herein, a novel acid‐responsive CPL tunable molecule is designed by combining an aggregation‐induced emission (AIE) component (TPE), an acid‐responsive luminophore (Rhodol), and a chiral aniline. Benefitting by the “AIE” effect of TPE and acid‐sensitive nature of Rhodol, the acidified molecule (S‐Rhodol‐TPE) exhibits a high PLQY even when doped in the polymer substrate at high concentrations. In addition, due to the fluorescence resonance energy transfer (FRET) process between TPE and Rhodol, the emission color of S‐Rhodol‐TPE can be easily regulated by the doped ratio and acidified degree of S‐Rhodol‐TPE in the polymer film. This work exhibits a unique approach to achieving smart CPL‐tunable films with high PLQYs and multiple emission color‐regulation properties, which can undoubtedly facilitate the progress of CPL tunable materials.

Lead-Free Perovskite With Efficient Tellurium Ion Activation for Multifunctional Applications.

Lead-free perovskite materials have received extensive attention due to their non-toxicity, super environmental stability and adjustable photoelectric properties. However, the inherent problems of low luminous efficiency and low photoluminescence quantum yields (PLQYs) limit its development in multifunctional applications. Here, Te4+ doped Cs2ZrCl6 with high luminous efficiency and stability for multifunctional applications are developed. Te4+ ions are used as emission centers to improve the optical properties of Cs2ZrCl6 to make efficient and stable single-component white light-emitting diodes (WLEDs), and can be used as scintillator materials to improve scintillation performance to achieve high-resolution and low-dose X-ray imaging detection. In addition, it is found for the first time that Te4+ ions can be introduced into the trap center, so that the Cs2ZrCl6:Te4+ perovskite material exhibits excellent persistent luminescence (PersL) and mechanoluminescence (ML) after X-ray radiation, which has potential applications in the fields of delayed imaging and stress sensing. This work provides a method for designing lead-free perovskites with high optical performance and scintillating properties, as well as developing multifunctional applications.

Reversible Structural Phase Transitions in Zero-dimensional Cu(I)-Based Metal Halides for Dynamically Tunable Emissions.

Exploring structural phase transitions and luminescence mechanisms in Zero-dimensional (0D) metal halides poses significant challenges, that are crucial for unlocking the full potential of tunable optical properties and diversifying their functional capabilities. Herein, we have designed two inter-transformable 0D Cu(I)-based metal halides, namely (C19H18P)2CuI3 and (C19H18P)2Cu4I6, through distinct synthesis conditions utilizing identical reactants. Their optical properties and luminescence mechanisms were systematically elucidated by experiments combined with density functional theory calculations. The bright cyan-fluorescent (C19H18P)2CuI3 with high photoluminescence quantum yield (PLQY) of 77% is attributed to the self-trapped exciton emission. Differently, the broad yellow-orange fluorescence of (C19H18P)2Cu4I6 displays a remarkable PLQY of 83%. Its luminescence mechanism is mainly attributed to the combined effects of metal/halide-to-ligand charge transfer and cluster-centered charge transfer, which effects stem from the strong Cu-Cu bonding interactions in the (Cu4I6)2- clusters. Moreover, (C19H18P)2CuI3 and (C19H18P)2Cu4I6 exhibit reversible structural phase transitions. The elucidation of the phase transitions mechanism has paved the way for an unforgeable anti-counterfeiting system. This system dynamically shifts between cyan and yellow-orange fluorescence, triggered by the phase transitions, bolstering security and authenticity. This work enriches the luminescence theory of 0D metal halides, offering novel strategies for optical property modulation and fostering optical applications.

Delocalizing electron distribution in thermally activated delayed fluorophors for high-efficiency and long-lifetime blue electroluminescence.

Blue thermally activated delayed fluorescent emitters are promising for the next generation of organic light-emitting diodes, yet their performance still cannot meet the requirements for commercialization. Here we establish a design rule for highly efficient and stable thermally activated delayed fluorescent emitters by introducing an auxiliary acceptor that could delocalize electron distributions, enhancing molecular stability in both the negative polaron and triplet excited state, while also accelerating triplet-to-singlet up-conversion and singlet radiative processes simultaneously. Proof-of-concept thermally activated delayed fluorescent compounds, based on a multi-carbazole-benzonitrile structure, exhibit near-unity photoluminescent quantum yields, short-lived delays and improved photoluminescent and electroluminescent stabilities. A deep-blue organic light-emitting diode using one of these molecules as a sensitizer for a multi-resonance emitter achieves a remarkable time to 95% of initial luminance of 221 h at an initial luminance of 1,000 cd m-2, a maximum external quantum efficiency of 30.8% and Commission Internationale de l'Eclairage coordinates of (0.14, 0.17).

Dramatic Impact of Materials Combinations on the Chemical Organization of Core-Shell Nanocrystals: Boosting the Tm3+ Emission above 1600 nm.

This article represents the first foray into investigating the consequences of various material combinations on the short-wave infrared (SWIR, 1000-2000 nm) performance of Tm-based core-shell nanocrystals (NCs) above 1600 nm. In total, six different material combinations involving two different types of SWIR-emitting core NCs (α-NaTmF4 and LiTmF4) combined with three different protecting shell materials (α-NaYF4, CaF2, and LiYF4) have been synthesized. All corresponding homo- and heterostructured NCs have been meticulously characterized by powder X-ray diffraction and electron microscopy techniques. The latter revealed that out of the six investigated combinations, only one led to the formation of a true core-shell structure with well-segregated core and shell domains. The direct correlation between the downshifting performance and the spatial localization of Tm3+ ions within the final homo- and heterostructured NCs is established. Interestingly, to achieve the best SWIR performance, the formation of an abrupt interface is not a prerequisite, while the existence of a pure (even thin) protective shell is vital. Remarkably, although all homo- and heterostructured NCs have been synthesized under the exact same experimental conditions, Tm3+ SWIR emission is either fully quenched or highly efficient depending on the type of material combination. The most efficient combination (LiTmF4/LiYF4) achieved a high photoluminescence quantum yield of 39% for SWIR emission above 1600 nm (excitation power density in the range 0.5-3 W/cm2) despite significant intermixing. From now on, highly efficient SWIR-emitting probes with an emission above 1600 nm are within reach to unlock the full potential of in vivo SWIR imaging.

Highly efficient and thermally stable photonic ceramic by controllable and full crystallization from glass

Polycrystalline ceramics are promising for a diverse range of applications in solid state laser, lighting, scintillator and optical storage. Unfortunately, current ceramic elaborations involves strict and complex synthetic procedures such as ultra-high pressure and vacuum processing. Here, we realize the tune of MgAl2Si4O12 and Mg2Al4Si5O18 phase formation in a glass by controlling the two crystal nucleation and growth individually, and obtain a polycrystalline non-stoichiometric Mg2-x/2Al4-xSi5+xO18:Eu2+ translucent ceramic by virtue of complete and congruent crystallization of the glass. Microstructural characterizations verify that the resulting ceramic exhibits dense and closely stacked micrometer-scale crystallites with very thin grain boundary structure. Chemical composition analysis by energy dispersive X-ray spectrometry revels the grain's composition is highly deviated from the stoichiometric Mg2Al4Si5O18, with atomic ratio Mg/Al/Si of 1.00: 1.46: 2.70. The precipitated non-stoichiometric Mg2-x/2Al4-xSi5+xO18, structurally having infinite channels z = 0.25 or 0.75 sites that run parallel to the c-aix, provides an robust crystal-field environment for Eu2+ 5d-4f transition. As a consequence, the ceramic produces intense emission with photoluminescence quantum yield (PLQY) up to 90 %, and excellent thermal stability emission with 70.1 % emission intensity at 420 K relative to that at room temperature, demonstrating it can be applied in high power lighting application with improved light quality by employing the ceramic as a color converter. Moreover, the ceramic also exhibits thermally stimulated luminescence at temperature reaching up to 700 K, originating from the deep electronic traps in Mg2-x/2Al4-xSi5+xO18 lattice with estimated trap depth of 0.73eV and 0.97eV. We also demonstrate the ceramic is hopeful for optical information storage application as the storage information can be retain well without vulnerable by the fluctuations of external environments due to the deep traps.

High efficiency in blue TADF OLED using favorable horizontal oriented host

An appropriate host featuring a wide band gap (Eg) and high triplet energy (T1) is crucial for facilitating highly efficient blue-light emitting devices. In this study, 4Ac26CzBz, a new host comprising acridan and carbazole moieties linked to a benzimidazole core, has been synthesized and characterized. Notedly, 4Ac26CzBz exhibits a wide optical gap (Eg) and high triplet energy (T1) of 3.3 and 3.0 eV, respectively, and has been proven a suitable host for blue thermally activated delayed fluorescence (TADF) OLED. By adopting 4TCzBN as a blue-light dopant, a remarkably high device external quantum efficiency of 35.8 % (59.8 cd/A and 62.8 lm/W) and a low turn-on voltage (<3 eV) have been demonstrated, with significant suppression of the efficiency roll-off, maintaining a high efficiency of 29.7 % as luminance at 1000 cd/m2. This excellent performance is deduced from the host’s ambipolar carrier transporting properties, which refer to its ability to transport both electrons and holes effectively, high photoluminescence quantum yield (PLQY) of 98.6 %, and highly horizontal orientation of transition dipole, as determined through diverse analytical measurements. The good material properties of 4Ac26CzBz and the high OLED performance reveal its potential for the next generation’s advanced display and lighting applications.

Asymmetric Synthesis of Chiral Calix[4]arenes with Both Inherent and Axial Chirality via Cobalt-Catalyzed Enantioselective Intermolecular C-H Annulation.

Inherently chiral calixarenes have garnered significant attention due to their distinctive properties, yet the development of efficient catalytic asymmetric synthesis methods remains a critical challenge. Herein, we report the asymmetric synthesis of calix[4]arenes featuring inherent or both inherent and axial chirality via a cobalt-catalyzed C-H activation/annulation strategy in high yield with excellent enantio- and diastereoselectivity (up to > 99% ee and > 20:1 dr). Electrooxidation was also suitable for this transformation to obviate the sacrificial metal oxidants, underscoring the environmentally friendly potential of this approach. A key octahedral cobaltacycle intermediate was synthesized and characterized, providing valuable insights into the mode of enantio- and diastereocontrol of this protocol. Noteworthy photoluminescence quantum yields of up to 0.94 were measured, underscoring the potential of these compounds in the domain of organic fluorescent materials.

Two-dimensional-lattice-confined single-molecule-like aggregates.

Intermolecular distance largely determines the optoelectronic properties of organic matter. Conventional organic luminescent molecules are commonly used either as aggregates or as single molecules that are diluted in a foreigner matrix. They have garnered great research interest in recent decades for a variety of applications, including light-emitting diodes1,2, lasers3-5 andquantum technologies6,7, among others8-10. However, there is still a knowledge gap on how these molecules behave between the aggregation and dilution states. Here we report an unprecedented phase of molecular aggregate that forms in a two-dimensional hybrid perovskite superlattice with a near-equilibrium distance, which we refer to as a single-molecule-like aggregate (SMA). By implementing two-dimensional superlattices, the organic emitters are held in proximity, but, surprisingly, remain electronically isolated, thereby resulting in a near-unity photoluminescence quantum yield, akin to that of single molecules. Moreover, the emitters within the perovskite superlattices demonstrate strong alignment and dense packing resembling aggregates, allowing for the observation of robust directional emission, substantially enhanced radiative recombination and efficient lasing. Molecular dynamics simulations together with single-crystal structure analysis emphasize the critical role of the internal rotational and vibrational degrees of freedom of the molecules in the two-dimensional lattice for creating the exclusive SMA phase. This two-dimensional superlattice unifies the paradoxical properties of single molecules and aggregates, thus offering exciting possibilities for advanced spectroscopic and photonic applications.

Efficient thermally activated delayed fluorescence materials from symmetric anthraquinone derivatives for high-performance red OLEDs

Constructing efficient red thermally activated delayed-fluorescence (TADF) materials for high-performance organic light-emitting diodes (OLEDs) remains challenging due to the formidable barrier of energy gap law. In this work, a design strategy of connecting two donor units to the adjacent positions of electron acceptor is proposed for creating red luminescent materials, and four Y-shaped TADF molecules consisting of strong electron-withdrawing anthraquinone (AQ) acceptor and triphenylamine or acridine-based donors are designed and synthesized. They exhibit strong red emissions (604−618 nm) in toluene solutions and orange/red emissions (566−608 nm) with good photoluminescence quantum yields (43−68%) in doped films, and enjoy small singlet-triplet energy gaps (0.02−0.10 eV) and fast reverse intersystem crossing processes (1.5–7.3 × 105 s−1), which are attributed to the unique Y-shape structure. A maximum external quantum efficiency of 19.5% with an electroluminescence peak at 616 nm is achieved for AQ-PTPA-based red doped device, representing the highest level for red TADF-OLEDs based on AQ acceptor in the literature. This work can provide guidance for the design of efficient red delayed-fluorescence molecules for the application in OLEDs.

Clar's Aromatic π-Sextet Rule for the Construction of Red Multiple Resonance Emitter.

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical bandgap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94% and horizontal dipole ratio of ~90%, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3%, with only a slight decrease of 3.7% at an elevated luminance level of 100,000 cd/m2.

To Maximize Luminescence for an Efficient Organic Solar Cell†

Comprehensive SummaryWith the continuous development of photovoltaic materials, organic solar cells (OSCs) have made remarkable advancements, surpassing a power conversion efficiency (PCE) of 20%. However, the PCEs of OSCs remain lower than that of inorganic solar cells due to significant energy losses, mainly stemming from the relatively large non‐radiative recombination losses (usually be expressed as ∆E3), resulting in low open‐circuit voltages. This can be achieved by reducing non‐radiative recombination, and hereby increasing the electroluminescence quantum efficiency (EQEEL) of the photo‐active layer. This review analyzes the significance of luminescence efficiency in achieving high‐performance OSCs by examining the reciprocal relationship between ∆E3 and EQEEL. High‐efficiency organic solar cells can also be used as effective organic light‐emitting diodes (OLEDs). The discussion provides insights into the influencing factors of EQEEL and the mechanisms for adjusting various parameters, which include enhancements in photoluminescence quantum yield and the proportion of radiative excitons. The objective is to offer insights into the crucial role of luminescence performance in OSC development, guiding researchers toward developing novel photovoltaic materials or optimization strategies to enhance the luminescence performance of the active layer in OSCs, fostering the simultaneous advancement of OSCs and OLEDs. Key Scientists

Realizing Stable Luminescence in Antimony Doped Hybrid Tin(IV) Chloride toward Full Spectrum WLED and Anticounterfeiting Applications.

The outstanding optical properties empower Sb3+-doped zero-dimensional hybrid metal halides as cutting-edge luminescent materials. In this research, we present an efficient hybrid tin chloride, TEA2SnCl6:Sb3+ (TEA = tetraethylammonium), with broad dual emission bands peaking in the blue and orange regions that arise from the singlet and triplet state emissions of [SbCl5]2-, respectively. TEA2SnCl6:Sb3+ demonstrates a high photoluminescence quantum yield (PLQY) of 83.5% under 328 nm excitation, while 358 nm light induces an orange emission with a PLQY of 92.5% and a low thermal quenching behavior (73.9% at 423 K). Benefiting from the appealing luminescence properties of TEA2SnCl6:Sb3+, a full spectrum white light-emitting diode (WLED) device and an anticounterfeiting model were constructed, affirming the potential use of Sb3+-doped TEA2SnCl6 hybrid metal halide in versatile application fields.

Narrowband Emission in Pt(II) Complexes via Ligand Engineering for Blue Phosphorescent Organic Light‐Emitting Diodes

AbstractIn this study, three stable tetradentate Pt(II) complexes are synthesized and characterized, namely, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu, tailored for blue phosphorescent organic light‐emitting diodes to realize high‐efficiency and narrowband emissions via ligand engineering. Biphenyl (Pt‐biPh) or tert‐butyl‐modified biphenyl (Pt‐biPh5tBu and Pt‐biPh4tBu) is introduced into the carbene unit of the ligand to control the intermolecular interactions between the Pt(II) phosphors. Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu exhibit high photoluminescence quantum yields of 74%, 84%, and 92% with exciton lifetimes of 2.2, 2.3, and 2.5 µs, respectively, demonstrating rapid and efficient light emission. Furthermore, Pt‐biPh, Pt‐biPh5tBu, and Pt‐biPh4tBu show maximum external quantum efficiency (EQE) values of 18.1%, 19.0%, and 21.8%, respectively. Pt‐biPh5tBu and Pt‐biPh4tBu exhibit narrowband emission with a full width at half maximum of 21 nm owing to the small vibrational emission because of their sterically hindered and bulky ligand structures. Moreover, phosphor‐sensitized thermally activated delayed fluorescence devices employing a Pt‐biPh4tBu sensitizer achieve a high EQE of 28.6%. In particular, Pt‐biPh4tBu performs better than the state‐of‐the‐art phosphor as the sensitizer of the blue phosphor‐sensitized thermally activated delayed fluorescence devices in terms of the EQE.