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In recent decades, numerous red phosphors have been designed and developed. Nevertheless, many of them are unsatisfactory due to their low brightness and poor thermal stability. Look at these shortcomings; present study reports on Eu3+ doped Y 2 Si 2 O 7 (YPS) phosphors, synthesized through low temperature based urea assisted gel-combustion method. Comprehensive investigations were conducted on phase purity, luminous characteristics, energy transfer mechanism, quantum efficacy, morphology, elemental makeup, band gap and thermal stability. XRD analysis was employed to verify the preparation of Y 2 Si 2 O 7 matrix with triclinic structure (P-1 space group). Morphology and elemental investigations of the fabricated materials was evaluated via TEM and EDX techniques respectively. Under the illumination at 393 nm, the most strong emission band is shown in PL spectra at 613 nm (electric dipole 5D 0 →7F 2 transition). Additionally, the dipole-quadrupole (d-q) interaction was found to be the predominant route of energy transfer among nearby Eu3+ ions and it was concluded that 3 mol % was the optimal doping concentration of Eu3+ ions. The Judd-Ofelt (J-O) theory was used for current phosphors in order to establish their Ω 2 and Ω 4 with other radiative parameters. The assessment of thermal stability yielded highly promising results with activation energy of 0.241 eV. Present research indicates that Y 2 Si 2 O 7 :Eu3+ is a promising candidate of red emitting phosphor for white light-emitting diodes. [Display omitted] • Gel-combustion derived Eu3+ doped Y 2 Si 2 O 7 nanophosphors were crystallized into triclinic symmetry with P–1 space group. • Dominance of electric dipole 5D 0 →7F 2 transition at 613 nm was observed which define the red color of synthesized nanophosphors. • The luminous thermal stability revealed 69.4 % of luminescence at 498 K with activation energy of 0.241 eV. • Colorimetric investigation of the synthesized Y 2 Si 2 O 7 :Eu3+ nanophosphors validate their applicability in white light applications. [ABSTRACT FROM AUTHOR]

A carbazole‐based hole‐transport‐type (p‐type) host, BPhCz, is developed using a nonsymmetrical connection strategy between two identical groups. Two benzimidazole–triazine‐based electron acceptor materials with superior electron transport abilities, namely SFX‐PIM‐TRZ and DSFX‐PIM‐TRZ, are designed to fabricate exciplex‐host systems combined with BPhCz. Exciplexes exhibit excellent carrier transport characteristics and appropriate energy levels and can serve as hosts for green multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) devices. Efficient green MR‐TADF organic light‐emitting diodes with high color purity and low efficiency roll‐offs are successfully fabricated using the exciplexes prepared from BPhCz:SFX‐PIM‐TRZ and BPhCz:DSFX‐PIM‐TRZ as hosts, which show low driving voltages of 2.6 and 2.7 V, high maximum external quantum efficiencies (EQEs) of 35.7% and 35.5%, ultrapure green emission with Commission Internationale de L'Eclairage coordinates of (0.27, 0.69) and (0.28, 0.69), and high EQEs of 31% and 30.5% at 1000 cd m−2, respectively. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescent (TADF) and phosphorescent blue organic light‐emitting diodes (OLEDs) have been developed to overcome the relatively low triplet exciton utilization of traditional fluorescent OLEDs. However, broad emission spectra originating from charge transfer process limit the commercial application of such blue OLEDs. Herein, an effective phosphor‐sensitized fluorescent (PSF) OLED device structure was designed. PSF OLED exhibited a maximum blue index (BI) of 508 cd/A/CIEy with CIEy of 0.060, which has been the highest efficiency result reported for PSF deep‐blue OLEDs. A nearly 100% improvement in operational lifetime LT95 (L/L0 = 95%) was achieved successfully by using lower triplet energy (T1) and deuterated host materials. Impressively, the sensitized OLEDs maintained BI of 407 cd/A/CIEy, narrow emission spectra (FWHM = 17 nm), and high color purity (CIEy = 0.046), revealing the attractive technical advantages and commercial application potential. [ABSTRACT FROM AUTHOR]

High color purity is one of the important features for single‐crystal metal halide perovskite light‐emitting diode (LED). Despite single‐crystal perovskite showing low bulk defect concentration, single‐crystal perovskite LEDs do not exhibit high color purity advantage due to the absence of effective surface defect passivation. Herein, one fully wrapped structure is proposed to passivate the surface of the free‐standing CsPbBr3 single‐crystal films. The surface of CsPbBr3 single‐crystal films is wrapped by ultra‐thin polymethyl methacrylate, precisely controlling the thickness. The single‐crystal perovskite film device can achieve high color purity with a full width at half maximum (FWHM) of 15.8 nm) and a large luminescent area of 2.25 mm2. It is observed that surface passivation is due to interaction of CO bond in polymer chains with the Lewis acid PbBr2. The passivated perovskite single‐crystal films significantly improve carrier lifetime and suppress surface defects. It is noteworthy that the passivated free‐standing single‐crystal perovskite films are feasible to build up a vertical LED device structure, avoiding the edge glowing and short‐circuiting of the LED device. This study demonstrates the large luminescent area of the high‐quality millimetre‐scale free‐standing single‐crystal films for wide color gamut display and vertical optoelectronic devices. [ABSTRACT FROM AUTHOR]

Inkjet printing technology offers a unique approach to producing direct-patterned pixels without fine metal masks for active matrix displays. Organic light-emitting diodes (OLEDs) consisting of thermally activated delayed fluorescence (TADF) emitters facilitate efficient light emission without heavy metals, such as platinum and iridium. Multi-resonance TADF molecules, characterized by their small full width at half maxima (FWHM), are highly suitable for the requirements of wide color-gamut displays. Herein, host-free TADF inks with a low concentration of 1 mg/mL were developed and inkjet-printed onto a seeding layer, concurrently serving as the hole-transporting layer. Attributed to the proof-of-concept of host-free inks printed on a mixed seeding layer, a maximum external quantum efficiency of 13.1% (improved by a factor of 21.8) was achieved in the inkjet-printed OLED, with a remarkably narrow FWHM of only 32 nm. Highly efficient energy transfer was facilitated by the effective dispersion of the sensitizer around the terminal emitters. [ABSTRACT FROM AUTHOR]

Advanced multiple resonance induced thermally activated delayed fluorescence (MR‐TADF) emitters have emerged as a privileged motif for applications in organic light‐emitting diodes (OLEDs), because they furnish highly tunable TADF characteristics and high color purity emission. Herein, based on the unique nitrogen‐atom embedding molecular engineering (NEME) strategy, a series of compounds BN‐TP‐Nx (x=1, 2, 3, 4) have been customized. The nitrogen‐atom anchored at different position of triphenylene hexagonal lattice entails varying degrees of perturbation to the electronic structure. The newly‐constructed emitters have demonstrated the precise regulation of emission maxima of MR‐TADF emitters to meet the actual industrial demand, and further enormously enriched the MR‐TADF molecular reservoir. The BN‐TP‐N3‐based OLED exhibits ultrapure green emission, with peak of 524 nm, full‐width at half‐maximum (FWHM) of 33 nm, Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.71), and maximum external quantum efficiency (EQE) of 37.3 %. [ABSTRACT FROM AUTHOR]

Rare-earth doped phosphors have received growing interest in the luminescence field, and hold great potential for lighting and display backlight applications. Nonetheless, the practical implementation of white light-emitting diodes requires the development of a cost-effective and high-performance red phosphor, which is still a significant challenge. In this paper, Eu3+ doped Ba3Na0.32Nb6O12(Si2O7)2 red phosphors were prepared using a high-temperature solid-state method. The structure and phase purity of the samples were analyzed in detail by powder X-ray diffraction (XRD), structure refinement and energy dispersive spectroscopy analysis. Under 395 nm excitation, the phosphor exhibited an intense red emission due to the 5D0 → 7FJ (J = 1, 2, 3, 4) transitions. Through decay curve measurements, it is found that the decay time corresponding to the double-exponential equation decreased with the increase of activator concentration. Theoretical calculations showed that the quadrupole–quadrupole interaction played a dominant role in concentration quenching. The CIE chromaticity coordinates of the phosphor were (0.6436, 0.3556) and the color purity reached 92.07%, indicating that the sample has high color purity. In addition, the temperature-dependent intensity was investigated in detail. The results demonstrated that Ba3Na0.32Nb6O12(Si2O7)2:Eu3+ is a potential red-emitting phosphor for near-ultraviolet based white light-emitting diodes. [ABSTRACT FROM AUTHOR]

Red phosphor plays a key role in improving the lighting and display quality of phosphor-converted white light-emitting diodes (pc-WLEDs). Meanwhile, developing new luminescent matrix materials can positively contribute to the acquisition of ideal and efficient phosphors. In this work, we propose a novel red-emitting Na 5 W 3 O 9 F 5 :Eu3+ (NWOF:Eu3+) phosphor. The phase composition, morphology, electronic structure and photoluminescence properties of the NWOF:Eu3+ phosphor were systematically investigated. The EXAFS results prove that the Eu3+ dopants occupy the Na2 and Na3 sites in the NWOF host. Under 466 nm blue light excitation, NWOF: x Eu3+ (0.05 ≤ x ≤ 0.25) phosphors display a dominant red emission at 607 nm and achieves a high color purity (97.44%) due to the dominant electric dipole transition (5D 0 →7F 2) of Eu3+ ions. Impressively, this red-emitting NWOF:0.25Eu3+ phosphor exhibits relatively superior thermal stability (450 K, >50%) and excellent chromaticity stability (2.32 × 10−4 ≤ ΔE ≤ 6.23 × 10−3) from 298 K to 498 K. The activation energy for thermal quenching effect is determined to be 0.22 eV. Moreover, the pc-WLED was fabricated by coupling a 460 nm blue chip with the as-synthesized NWOF:0.25Eu3+ red phosphor and commercial YAG:Ce3+ phosphor. The optical parameters of the as-fabricated pc-WLED are also measured, and the CIE coordinates remain almost constant as the drive current increases from 20 mA to 120 mA. These results indicate that the NWOF:0.25Eu3+ red phosphors should be a suitable candidate as a red component for the preparation of pc-WLEDs. [Display omitted] [ABSTRACT FROM AUTHOR]

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters have been studied to address the issue of the broadband emission in organic light‐emitting diodes (OLEDs). Herein, the authors have systematically investigated the effect of electron‐donating or ‐withdrawing units in the para position of B atom on the optoelectronic emission modulation BCz‐BN MR‐TADF emitters. Due to the enhanced spin‐orbit coupling (SOC) effect, BN(p)SCH3 with electron structure of para‐D‐π‐B is synthesized by introducing a heavy S atom into the para position of B atom of BCz‐BN. By oxidizing BN(p)SCH3, BN(p)SOCH3 and BN(p)SO2CH3 with electron structure of para‐A‐π‐B have been synthesized. The quantum simulations and photophysical studies have illustrated BN(p)SCH3 can exhibit large reverse intersystem crossing rate constant (kRISC) of 6.4 × 104 s−1 due to the large SOC constants and small singlet‐triplet energy splitting (ΔEST) of 0.12 eV. BN(p)SOCH3 and BN(p)SO2CH3 with electron structure of para‐A‐π‐B displayed red‐shift emissions with smaller full‐width at half‐maximum (FWHM) values of ≈21 nm and kRISC values owing to enhanced ΔEST and the low emission contribution of the triplet excitons in contrast to those of BN(p)SCH3 with electron structure of para‐D‐π‐B. Consequently, BN(p)SCH3‐based OLEDs show highly efficient blue emission with an external quantum efficiency (EQE) of 26.2% and excellent color purity. [ABSTRACT FROM AUTHOR]

The development of efficient ultraviolet (UV) organic light-emitting materials and devices holds paramount significance for their practical applications. Nonetheless, attaining a short-wavelength electroluminescence peak of less than 390 nm while maintaining high color purity in non-doped devices remains a formidable challenge. In this work, we have successfully designed and synthesized two UV hybridized local and charge transfer fluorophores, specifically 4DBF-CZCN and 2DBF-CZCN, which are comprised of cyanide-modified phenylcarbazole and a weak electron donor dibenzofuran. And the properties of excited state are well regulated through the different linking site of dibenzofuran. The resulting non-doped devices exhibit not only emission peak wavelengths of 390 and 388 nm, accompanied by narrow full-width-at-half-maximums of 42 and 38 nm, respectively, corresponding to color coordinates of (0.164, 0.034) and (0.164, 0.036), but also admirable external quantum efficiencies of 3.00 % and 2.86 % at high luminance levels of 1910 and 1252 cd m−2, respectively. Two ultraviolet fluorophores with hybridized local and charge transfer state were developed by incorporating N -(4-cyanophenyl)carbazole framework with ancillary donor dibenzofuran. [Display omitted] • Two ultraviolet fluorophores with HLCT excited state were designed and synthesized. • The non-doped devices emit stable ultraviolet light with peaks of 390 and 388 nm. • Maximum EQE of ∼3.0 % was achieved at a high luminance of 1910 cd m−2. [ABSTRACT FROM AUTHOR]

Multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters are very promising in the high‐resolution and high‐efficiency displays, due to their narrow and highly efficient optical emissions. Early MR‐TADF cores that show only short‐range charge‐transfer (CT) electronic excitations hardly afford ideal performances (e.g., show low efficiencies) in organic light‐emitting diodes (OLEDs). This work thus designs and synthesizes two MR‐TADF emitters (TCzBN‐BP and TCzBN‐FP), where the same MR core TCzBN is chemically modified by the acceptor fragments benzophenone/9‐fluorenone (BP/FP) to incorporate long‐range CT excitations in the two molecules. OLEDs exploiting TCzBN‐BP as emitter, in which short‐range CT excitation is dominant in the first singlet (S1) excited state, achieve a maximum external quantum efficiency (EQE) of 35.6% and a narrow emission bandwidth of 35 nm. In contrast, OLEDs exploiting TCzBN‐FP with an overloaded long‐range CT excitation in the S1 state exhibit a maximum EQE of 27.2% and a broadened emission bandwidth of 56 nm. This work not only shows the importance of careful management of long‐ and short‐range CT excitations, but also provides a new insight into the structure–property relationship in the MR‐TADF emitters, which thus promotes the design of more novel MR‐TADF emitters with high efficiencies and high color purity. [ABSTRACT FROM AUTHOR]

• MgTi 2 O 5 : xEu3+ phosphors are synthesized by solid-state reaction method. • Under 465 nm excitation, intense red emission was obtained at 615 nm. • Internal quantum efficiency of the phosphor was determined to be 31.65 %. • Phosphors have high color purity and warm light emission. • Synthesized red phosphor is a suitable candidate for pc-wLEDs. As one of the critical components for achieving high-quality white light emitting diodes (w-LEDs) are efficient phosphors, a series of intense red emitting Eu3+doped magnesium dititanate (Mg (1- x) Ti 2 O 5 : x Eu3+; x = 0, 0.005, 0.008, 0.01, 0.02 and 0.03 mol) phosphors were prepared via solid-state reaction method. The X-ray diffraction (XRD) patterns confirmed the phase purity and orthorhombic structure of the prepared phosphors. The Ti-O functional groups were detected from the Fourier transform infrared (FTIR) spectra and Field emission scanning electron microscopy (FESEM) images revealed agglomerated spherical-like shaped phosphor particles. Under 465 nm excitation, intense red emission corresponding to 5D 0 →7F J (J = 0, 1, 2, 3, and 4) transitions of Eu3+ ions were recorded in the photoluminescence (PL) spectra with an intense peak at 615 nm. The optimum concentration of Eu3+ ions was determined to be 1 mol% and the concentration quenching mechanism was due to the interaction between adjacent Eu3+ ions. The lifetime values of the samples were in the millisecond range and the internal quantum efficiency was determined to be 31.65 %. The Commission Internationale de l'Eclairage (CIE) coordinates of the optimum sample Mg 0.99 Ti 2 O 5 :0.01Eu3+ are (0.6421, 0.3575), lies in the red region with 99.9 % color purity and have warm correlated color temperature (CCT) values. Therefore obtained results suggest that the prepared Mg (1- x) Ti 2 O 5 : x Eu3+phosphors can be used as an efficient red phosphor for w-LED applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The novel orange-red emitting K 5 Y(MoO 4) 4 : x Sm3+ (KYMO: x Sm3+) (1 mol% ≤ x ≤ 35 mol%) phosphors were synthesized through solid-phase reaction. The KYMO:Sm3+ phosphors were mainly analyzed for purity phase, luminescence properties, and thermostability. Under 403 nm excitation, KYMO:10 mol%Sm3+ possesses four distinct emission peaks. The dominant emission peak is situated at 645 nm, corresponding to the 4G 5/2 → 6H 7/2 electron transitions. With x = 10 mol%, the KYMO: x Sm3+ phosphor has the optimal doping concentration. The color purity reaches as high as 99.9 %. KYMO:10 mol%Sm3+ presents good thermostability with T 0.5 > 480 K and resistance to color drift (Δ E = 0.012 at 420 K). The lifetime for KYMO:10 mol%Sm3+ is 1.16 ms. The internal quantum efficiency (IQE) reaches 62.74 %. At 480 K, the maximum temperature sensing sensitivities of the FIR of I 564 /I 599 are 5.19 × 10−4 (S a) and 18 % (S r). The assembled WLED displays an excellent color rendering index (CRI, R a) of 94, Commission International de L′ Eclairage (CIE) coordinates (0.333, 0.346), and a correlated color temperature (CCT) of 5464 K. In summary, KYMO:Sm3+ phosphors possess great promise for high CRI white-light-emitting diodes (WLEDs) and potential feasibility for temperature sensing. • K 5 Y(MoO 4) 4 :Sm3+ phosphors have been synthesized via solid-state reaction firstly. • The phosphor emits bright orange-red light excited by 403 nm. • The synthesized phosphors exhibit the superior color purity (99.8 %–99.9 %). • The fabricated WLED exhibits a high color rendering index (R a = 94). [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) emitters induced by the multiple resonance (MR) effect have garnered considerable attention. However, it is difficult to develop MR‐TADF emitters that maintain high color purities in the red region. In this work, the importance of excited state alignments of MR‐based donor‐acceptor (D‐A) molecules in determining their preferring characteristics is clarified. By using the newly designed molecule mBDPA‐TOAT whose apparent excited states show hybridization of MR and intersegmental charge‐transfer features as an emitter in an organic light‐emitting diode (OLED), a high external quantum efficiency of 17.3% is achieved with a full width at half‐maximum of 45 nm (154 meV) and Commission Internationale de L'Éclairage coordinate of (0.61, 0.39). This work demonstrates when introducing D‐A typed structures, features, and alignments of molecular excited states determine ultimate material properties. This could help to develop high efficiency and high color purity TADF emitters toward long wavelength range. [ABSTRACT FROM AUTHOR]

To enhance the display quality of light‐emitting diodes (LEDs), it is of great significance to exploit green/yellow‐emitting phosphors with narrow emission band, high quantum yield, and excellent color purity to satisfy the application. Herein, orthophosphate‐based green/yellow‐emitting Na3Tb(PO4)2:Ce3+/Eu2+ (NTPO:Ce3+/Eu2+) phosphors have been successfully synthesized by a facile solid‐state reaction method. The absorption band of NTPO samples was extended to the near‐ultraviolet region and the absorption efficiency was significantly improved owing to a highly efficient energy transfer from Ce3+/Eu2+ ion to Tb3+ ion in NTPO host certified by time‐resolved PL spectra. Upon 300 nm excitation, the NTPO:Ce3+ is characterized by ultra‐narrow‐band green emission of Tb3+ with an absolute quantum yield of 94.5%. Unexpectedly, NTPO:Eu2+ emits bright yellow light with a color purity of 73% as a result of the blending of green light emission from Tb3+ and red light emission from Eu3+. The thermal stability has been improved by controlling the stoichiometric ratio of Na+. The prototype white LED used yellow‐emitting NTPO:Eu2+ phosphor has higher color‐rendering index (Ra = 83.5), lower correlated color temperature (CCT = 5206 K), and closer CIE color coordinates (0.338, 0.3187) to the standard white point at (0.333, 0.333) than that used green‐emitting NTPO:Ce3+ phosphor, indicating the addition of the yellow light component improved the Ra of the trichromatic (RGB) materials. [ABSTRACT FROM AUTHOR]

Purely organic compounds with thermally activated delayed fluorescence (TADF) are promising sustainable emitters for organic light‐emitting diodes. But the simultaneous realization of a high efficiency, short lifetime, and good color purity in single TADF molecule remains challenging. Herein it is reported that the confinement of rigid and planar N‐ and B‐centered donor and acceptor in sandwich‐type structures, named BNB‐m and BNB‐p, can lead to green TADF emissions with up to unity efficiency and improved color purity from through‐space charge‐transfer excited states. The full width at half maximum of 58 nm (0.28 eV) for BNB‐m is significantly smaller than those for most of the TADF emitters having a twisted donor‐acceptor structure. Single‐crystal structures, NMR spectroscopy, and theoretical simulations manifest the presence of strong noncovalent π‐stacking interactions in BNB‐m which account for the reduced intramolecular motions and enhanced through‐space electronic coupling. With a relatively short delayed fluorescence lifetime of 11 µs, the emitter BNB‐m demonstrates attractive green electroluminescence with a maximum external quantum efficiency (EQE) of 34.9% and an EQE of 27.4% at 1000 cd m−2. This work validates a promising molecular design to TADF emitters which can realize a balanced emission property in terms of color purity and emission lifetime. [ABSTRACT FROM AUTHOR]

Despite concrete efforts to Ir(III)-complex-based NIR-OLEDs/PLEDs, most of them previously reported are not of color-purity NIR-emission, due to the considerable visible-light remnants in the NIR-emissive protocols. Meanwhile, for the limited Ir(III)-complex-based color-purity NIR-OLEDs/PLEDs, it remains a great challenge to realize their high-performance, besides the tackling of non-all-solution-processed operation cost. In this paper, based on the molecular design of [Ir (dpbq) 2 (Ln)] (1 – 2 , n = 1–2), the highly conjugated HC^N-main ligand Hdpbq renders its Ir(III)-complexes' desirable color-purity NIR-phosphorescence (λ PL = 780 nm), while electrochemical properties and excited-state dynamics are deeply dependent on the varied N^OH-ancillary ligands with different electronic effects. Especially for the [Ir (dpbq) 2 (L2)] (2), its color-purity NIR-phosphorescent high-efficiency (Φ PL = 3.6 %) is arisen from augmented 3MLCT effect and large transition dipole moment (TDM). Importantly, upon its all-solution-processing device fabrication, the first-example of all-solution-processed and color-purity NIR-PLED (λ EL = 780 nm; η EQE Max = 1.4 %), the best of our knowledge, was realized. Using [Ir (dpbq) 2 (Ln)] (1 – 2 , n = 1–2) characteristic of color-purity NIR-phosphorescence (λ em = 780 nm) as dopants, the first-examples of all-solution-processed and color-purity NIR-PLEDs were realized. Especially for the [Ir (dpbq) 2 (L2)] (2), its high-efficiency (Φ PL = 3.6 % and η EQE Max = 1.4 %) is arisen from augmented 3MLCT effect and large transition dipole moment (TDM). [Display omitted] • C 1 -symmetric [Ir(C^N) 2 (N^O)]- bis -heteroleptic Ir(III)-complexes. • Color-purity near-infrared emission. • All-solution-processed polymer light-emitting diodes (PLEDs). [ABSTRACT FROM AUTHOR]

Laser illumination is considered to be a revolution of new lighting technology due to its high efficiency and pure color. Similar to the white Light Emitting Diode (LED), phosphor convertor is also a necessary component to generate light in laser illumination technology. In order to improve the performance of laser, designing and optimizing phosphor with high color purity is an effective method. In our study, the pure-red Sr2GdTaO6:Er3+/Yb3+ powders were synthesized and optimized using a high-temperature solid-phase method. The phosphor structure of the obtained phosphors was analyzed through X-ray diffraction (XRD), confirming all products are Sr2GdTaO6 polycrystalline powders. Theoretical models, optimized through experimental design, established regression equations correlating Er3+/Yb3+ doping concentrations with luminescence intensity. Leveraging a genetic algorithm, the optimal solutions for the equations were calculated, resulting in Er3+ and Yb3+ doping concentrations of 4.99% and 24.85% under 980 nm laser excitation and 4.95% and 23.19% under 1550 nm laser excitation, respectively. Under the same conditions, the up-conversion fluorescence emission spectra of the samples were measured, revealing strong green and red emissions with peaks at 550 nm, 563 nm, and 663 nm, corresponding to transitions from 2H11/2 → 4I15/2, 4S3/2 → 4I15/2, and 4F9/2 → 4I15/2 energy levels. For the optimal samples at 980 nm and 1550 nm, the relationship between up-conversion luminescence and laser operating current was explored, indicating that the up-conversion luminescence in these two cases is a two-photon and three-photon process, respectively. The up-conversion luminescence mechanism was analyzed and discussed in detail. Additionally, the relationship between up-conversion fluorescence and temperature was investigated for the optimal samples, revealing excellent temperature-sensing characteristics for up-conversion emissions excited by both 980 nm and 1550 nm lasers. The CIE coordinates (0.5986, 0.3973) and (0.7089, 0.2910) of the optimal sample were calculated under excitation at 980 nm and 1550 nm wavelengths. [ABSTRACT FROM AUTHOR]

With the increasing performance demand from the display market, it has become ever more important to realize wide color gamut requirement. In this paper, we fabricated a series of pTSF green devices, the optimal devices which exhibit excellent performance in the range of CIEx 0.17‐ 0.22, with the central color point meeting Adobe's green light requirements, showing the advantages in wide color gamut. Additionally, they have comparable performance to existing phosphporescent devices under DCI‐P3 light color, showing the advantages of high performance and high color purity. [ABSTRACT FROM AUTHOR]

Borate oxyfluoride glasses are transparent in the infrared, ultraviolet and visible regions and represent an ideal host matrix for optically active dopants. Due to their lower phonon energies compared to a silicate glass matrix, non-radiative transitions are suppressed and high luminescence efficiency is expected. This work reports on a complete upconversion (UC) luminescence study of the optically active B2O3–Al2O3–KF–LiO (BAKL) glass-ceramics incorporated with Er3+/Yb3+ ions. The triclinic BAKL:Er3+/Yb3+ glass-ceramic (GC) phosphor was synthesized using the conventional melt-quenching technique and the subsequent heat treatment of the precursor glass. The successful synthesis of BAKL:Er3+/Yb3+ GCs was confirmed by X-ray diffraction, Fourier transform infra-red and differential thermal analysis measurements. The glasses were crystallized under controlled conditions, and the influence of phase composition (glass-to-crystalline phase ratio) on the wavelength and UC luminescence was thoroughly studied under 980 nm excitation. Interesting color tuning properties (white to intense green emission) of the sample were observed with laser pump power increment. The color tuning properties were explained using a new strategy i.e. the energy bridging mechanism between Er3+ ion clusters through an intermediate Yb3+ level. Moreover, their high color purity is well retained by varying the NIR excitation pump power densities and photometric characterization indicated the suitability in light emitting diodes and Er3+ doped fiber amplifier applications. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials based on multiple resonance (MR) effect exhibit enormous potentials in organic light‐emitting diodes (OLEDs) with high color purity due to their intrinsically narrow emission. However, most of MR‐TADF emitters are limited to the boron‐nitrogen‐based rigid skeleton. In this work, three novel MR‐TADF emitters, namely CzBNO, DMAcBNO and DPAcBNO, are elaborately constructed, the TADF properties of which are realized by virtue of opposite MR effect of boron and nitrogen/oxygen atom. CzBNO‐based deep blue‐emitting OLEDs achieve a maximum external quantum efficiency (EQE) of 13.6% with a small FWHM of 36 nm, as well as a Commission Internationale de l'Eclairage (CIE) coordinate of (0.14,0.08). While the other two emitter‐based devices exhibit blue emission with a maximum EQE of up to 23.0%. To further improve the OLEDs performances, DMAcBNO and DPAcBNO‐based devices assisted by a sensitizer exhibit an excellent EQE of up to 29.6% with a relatively small efficiency roll‐off. [ABSTRACT FROM AUTHOR]

Multiple resonance thermally activated delayed fluorescence (MR‐TADF) compounds have set off an upsurge of research because of their tremendous application prospects in the field of wide color gamut display. Herein, we propose a novel MR‐TADF molecular construction paradigm based on polycyclization of the multiple resonance parent core, and construct a representative multiple resonance polycyclic aromatic hydrocarbon (MR‐PAH) based on the para‐alignment of boron and nitrogen atoms into a six‐membered ring (p‐BNR). Through the retrosynthesis analysis, a concise synthesis strategy with wide applicability has been proposed, encompassing programmed sequential boron esterification, Suzuki coupling and Scholl oxidative coupling. The target model molecule BN‐TP shows green fluorescence with an emission peak at 523 nm and a narrow full‐width at half‐maximum (FWHM) of 34 nm. The organic light‐emitting diode (OLED) employing BN‐TP as an emitter exhibits ultrapure green emission with Commission Internationale de L'Eclairage (CIE) coordinates of (0.26, 0.70), and achieves a maximum external quantum efficiency (EQE) of 35.1 %. [ABSTRACT FROM AUTHOR]

In this study, Sm3+‐doped double‐perovskite Mg2InSbO6 phosphors were synthesized via high‐temperature solid‐state reaction. Mg2InSbO6 belongs to the double‐perovskite family with a space group of R3¯ (No.148). The photoluminescence (PL) spectrum illustrates that Mg2InSbO6:0.05Sm3+ phosphor can emit intense orange‐red emission light at 607 nm due to the 4G5/2→6H7/2 transition. The optimum concentration of Mg2InSbO6:xSm3+ is confirmed to 0.05 mol. The asymmetric ratio (4G5/2→6H9/2/4G5/2→6H5/2) of Mg2InSbO6:0.05Sm3+ phosphor is 2.73. The quenching temperature exceeds 500 K, illustrating that Mg2InSbO6:Sm3+ sample has excellent heat resistance. The high color purity and correlated color temperature (CCT) of Mg2InSbO6:Sm3+ phosphors are obtained. Furthermore, a white light‐emitting diode (w‐LED) is successfully fabricated, possessing CCT of 6769 K and high color rendering index (Ra) of 89. Therefore, the orange‐red‐emitting Mg2InSbO6:Sm3+ phosphors exhibit great potential to apply in solid‐state lighting fields. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) have broad application prospects in displays such as full-color light-emitting diodes (LEDs) and micro-LEDs. However, an ultrahigh concentration of QDs is required to eliminate the pumping light for achieving high color purity, leading to significant reduction in the photoluminescence (PL) intensity of the QDs and the generation of much more heat. In this article, the PL intensity, thermal performance, and color purity of QD-LEDs were comprehensively improved by introducing a pumping-light absorber (PLA). Results indicate that the PLA packaging structure achieves a color purity that is similar to that of a conventional structure with ultrahigh QD concentration; the radiant power of blue light was reduced by 81.6% and this leads to a large shift in the color coordinates from (0.18, 0.26) to (0.20, 0.57). Moreover, the PLA packaging structure results in higher electroluminescence (EL) intensity and lower operating temperatures than the conventional structure. This is because of the higher color-conversion efficiency and partial transfer of thermal energy to the PLA layer. In particular, the EL intensity of the QD-LEDs increased by 25.1% and the steady-state temperature was reduced to 58.9 °C, which is 19.75% lower than that of a conventional structure (73.4 °C). In addition, the PLA packaging structure works equally well with ultraviolet (UV) pumping sources to achieve a higher color purity (enhancing the color gamut by 50.1% when using a 405-nm source). [ABSTRACT FROM AUTHOR]

[Display omitted] • Phenoxazine and phenothiazine-embedded MR emitters are designed. • The designed MR emitters show red emission with superb photophysical properties. • OLEDs devices achieve high efficiency up to 34.5% and small efficiency roll-off. • Optimized device shows CIE coordinates (0.69, 0.31), approaching BT.2020 standard. Multi-resonance (MR) emitters based on boron-nitrogen doped polycyclic aromatic hydrocarbons are the cutting-edge light-emitting materials for organic light-emitting diodes (OLEDs) due to their high photoluminescence quantum yield and narrowband emission spectra. Among all the widely-reported MR molecules, emitters showing pure-red emission are the least developed. The difficulty in designing pure-red MR emitters lies in the limit of the weak charge transfer nature of the MR framework, as well as the large molecular weight which may bring difficulty in vacuum sublimation process. Herein, through introducing the strong electron donating phenoxazine and phenothiazine moiety into the double-boron-based MR molecular skeleton, two novel MR emitters namely PXZBNO and PTZBNO were designed and synthesized. These two emitters exhibited pure-red emission with emission maxima up to 627 nm, small full-width at half-maximum (FWHM) of 45 nm. Red OLEDs based on PTZBNO demonstrated very high maximum external quantum efficiency (EQE max) of 34.5%, together with very small efficiency roll-off. Meanwhile, PXZBNO -based purity pure-red OLEDs exhibited high color purity with color coordinates of (0.69, 0.31), which is approaching BT. 2020 standard. [ABSTRACT FROM AUTHOR]

We have developed high-brightness, high-color-purity, white organic light-emitting diodes featuring three emission layers: (i) the green light-emitting material 1,3,5-tris(1-pyrenyl)benzene (TPB3), (ii) the host material 1,4-bis(2,2-diphenylvinyl)biphenyl (DPVBi) doped with the blue dye di(4-fluorophenyl)amino-di(styryl)biphenyl (DSB), and (iii) tris(8-hydroxyquinoline)aluminum (Alq3) doped with the red dye 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). A device having the configuration indium tin oxide (1300 Å)/N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (500 Å)/TPB3 (200 Å)/DPVBi: 2 wt % DSB (150 Å)/Alq3: 2 wt % DCJTB (150 Å)/Alq3 (350 Å)/LiF (8 Å)/Al (2000 Å) exhibited a white emission with a maximum luminance at 15 V of 55 800 cd/m2, a maximum current efficiency of 4.06 cd/A at 13 V, a maximum power efficiency of 2.24 lm/W at 5 V, and a maximum external quantum efficiency of 2.45% at 5 V. The Commission Internationale de l’Eclairage coordinates of (0.33, 0.32) changed only slightly upon varying the potential from 9 to 13 V. We attribute the high brightness and color purity of the emitted white light to the high electroluminescence of the hosts and dopants, the relatively high efficiency of the energy transfer from the hosts to the dopants, and the high control over the thicknesses and dopant concentrations of the red-, green-, and blue-emitting layers, resulting in suitable numbers of partial excitons being generated in each of those three layers. [ABSTRACT FROM AUTHOR]

Abstract A deep-blue emitting poly(2′,3′,6′,7′-tetraoctyl-2,7-spirosilabifluorene), namely PSSiBF, has been newly developed for PLEDs. Unlike the previously-reported alkyl-functionalized P27SiF, the unwanted aggregation can be effectively prevented in PSSiBF due to the perpendicular arrangement between two spiro-linked dibenzosilole moieties. Compared with P27SiF (Φ PL = 0.62), consequently, an improved PLQY of 0.84 is obtained for the film of PSSiBF accompanied by a significant reduction of the long-wavelength emission in the range of 450–550 nm. Based on a double-layer device configuration, PSSiBF gives a bright deep-blue electroluminescence, revealing a state-of-art EQE of 2.8% and CIE coordinates of (0.16, 0.06). The simultaneous realization of good color purity and high EQE clearly implies that the silicon-containing polymers do have the great potential in efficient PLEDs. Graphical abstract The introduced spiro-linkage into the silicon-containing polymer has been demonstrated to effectively prevent the unwanted aggregation, leading to deep-blue electroluminescence with CIE coordinates of (0.16, 0.06). Image 1 Highlights • A deep-blue emitting poly(2',3',6',7'-tetraoctyl-2,7-spirosilabifluorene) has been newly developed for efficient PLEDs. • The unwanted aggregation can be effectively prevented by the perpendicular arrangement. • PSSiBF shows a bright deep-blue electroluminescence, revealing the EQE of 2.8% and CIE coordinates of (0.16, 0.06). [ABSTRACT FROM AUTHOR]

In this work, we synthesized and characterized a narrow band red emitting Gd 3 Zn 2 Nb 3 O 14 :Eu 3+ phosphor in order to improve the color qualities of warm white light emitting diodes. The phosphors were synthesized via conventional solid state reaction method and investigated the evolution of emission spectra with partial occupation of Zn 2+ ions on both A and B site of the fergusonite type structure. The structural and luminescence property analysis corroborates the occupancy of Eu 3+ ions in the Gd 3+ /Zn 2+ ion site (A site). The developed phosphor exhibits a strong red emission peaking at 613 nm with a fwhm of merely ∼3.50 nm under the 392 nm excitation. These compounds produce narrow emissions in the visible red spectral regions that are highly professed by human eye and lead to outstanding chromatic saturation of the red spectra. The enhanced electric dipole transition intensity arises from the symmetry distortion of Eu 3+ ions caused by the introduction of Zn 2+ ions in the lattice. The distortion of the A site symmetry and the red shift of the charge transfer energy leads to an intense 5 D 0 – 7 F 2 hypersensitive electric dipole transition under 392 nm excitation. The relative emission intensity was found to be maximum at x  = 0.40 and is 3.9 times higher than that of the commercial red phosphor under the 392 nm excitation. These phosphors with remarkable CIE chromaticity coordinates (0.64, 0.35), good CCT values along with high color purity (94.2%) might have significant applications in display devices and evidence as an efficient red phosphor. [ABSTRACT FROM AUTHOR]

• Highly efficient Li 2 MgTi 3 O 8 :Eu3+ phosphors have been synthesized for the first time by solid state reaction method. • Li 2 MgTi 3 O 8 :Eu3+ phosphors have an intense emission at 615 nm corresponding to red light upon 398 nm excitation. • The prepared phosphor possesses high color purity and warm CCT values. • Li 2 MgTi 3 O 8 :Eu3+ phosphors have the potential to be used as a red component in pc-WLEDs under UV excitation. In search of efficient and suitable phosphors for white light emitting diodes (w -LEDs), herein, we report Li 2 MgTi 3 O 8 :Eu3+ as red phosphors that are low-cost eco-materials synthesized by solid-state reaction method. XRD patterns confirm the crystallinity and phase purity of the as-prepared phosphors with the successful incorporation of Eu3+ ions. FTIR, FE-SEM and TEM were used to understand the functional groups and morphology of prepared samples respectively. The band gap energy calculated from DRS showed Burstein–Moss effect. Under 398 nm excitation, intense red emission was recorded at 615 nm and lifetime values were in microsecond range. The prepared phosphor possesses quantum efficiency of 31.74%, good thermal stability with an activation energy of 0.254 eV and exhibit warm red emission with 100% color purity. Therefore, the obtained results suggests that the prepared Li 2 MgTi 3 O 8 :Eu3+ phosphors can be considered as an appropriate candidate for the red component in w- LEDs. [Display omitted] [ABSTRACT FROM AUTHOR]

With the increasing performance demand from the display market, it has become ever more important to realize wide color gamut and low power consumption. Employing a phosphorescence‐sensitized fluorescence (PSF) mechanism, we introduced a narrow‐spectrum green light‐emitting layer (EML) to the state‐of‐the‐art OLED device structure suitable for mass production and investigate its effect on device performance. Compared with the reference phosphorescent device, the optimal PSF devices have achieved more than 20% efficiency improvement in the range of CIEx 0.17‐ 0.27, showing the advantages of high efficiency and high color purity. [ABSTRACT FROM AUTHOR]

In this work, a novel fluoroaluminate red phosphor of Cs2NaAl3F12:Mn4+ with excellent color purity was fabricated via the introduction of Mn4+ in the octahedral center. The crystal and electronic structures, luminescence properties and optical performances were characterized and investigated in detail. The evidences showed that Cs2NaAl3F12:Mn4+ well-crystallized into a single phase with particulate morphology, and the non-equivalent occupation in Cs2NaAl3F12 resulted in sharp red emissions with improved color purity upon blue light illumination. For solid-state lighting, the optical parameters consisted of the "blue-yellow-red" contributions significantly improved to a high color-rendering index of 88.7 and a low color temperature of 3856 K, indicating the potential use of Cs2NaAl3F12:Mn4+ for warm white light-emitting diode applications. [ABSTRACT FROM AUTHOR]

The thermal stable Eu(HCOO) 3 red-emitting crystals were synthesized by a facile hydrothermal route. Both excitation and emission spectra revealed that the prepared crystals can be efficiently pumped by the near-ultraviolet (NUV) light and it can emit brightness red light with admirable color purity of 90.4%. With the help of Judd-Ofelt theory, the optical transition intensity parameters of Eu3+ ions were evaluated so as to explore its local symmetry performance in the Eu(HCOO) 3 host lattices. The thermal quenching behaviors of the studied samples were investigated through the temperature-dependent emission spectra. Ultimately, a white light-emitting diode (WLED) lamp with good color rendering index (78.2) and correlated color temperature (6386 K) was packaged through coating the tricolor phosphors (BaMgAl 10 O 7 :Eu2+ blue-emitting phosphor, (Ba,Sr) 2 SiO 4 :Eu2+ green-emitting phosphor and resultant red-emitting crystals) onto the surface of a NUV chip. These results disclosed the high brightness Eu(HCOO) 3 red-emitting crystals were suitable for NUV chip triggered WLED applications. • The resultant crystals emitted glaring red emission with high color purity of 90.4%. • The local symmetry properties of Eu3+ ions were studied by Judd-Ofelt theory. • The crystals exhibited splendid thermal stability with activation energy of 0.16 eV. • The LED device can emit bight white light with proper CCT and CRI values. [ABSTRACT FROM AUTHOR]

Abstract Two tris-cyclometalated heteroleptic iridium complexes incorporating 2-(2,4-difluorophenyl)pyridine (dfppy) as the main cyclometalating ligand, 2′,6′-Difluoro-2,3′-bipyridine (dfbpy) or 3-(1-benzyl-1 H -1,2,3-triazol-4-yl)pyridine (pt) as the second cyclometalating ligand, namely Ir(dfppy) 2 (pt) (M 1) and Ir(dfppy) 2 (dfbpy) (M 2), were developed for application as blue phosphors in organic light-emitting diodes (OLEDs). The spectroscopic behavior of the complex phosphors was correlated with the ligand properties. With incorporation of the high-triplet-energy pt as the second cyclometalating ligand in Ir(dfppy) 2 (pt), the phosphorescence spectrum was slightly hypsochromatically shifted and narrowed with reduced intensity in long-wavelength vibration band, resulting in improved blue color purity in comparison with the traditional sky-blue iridium complex FIrpic. In simple-structure phosphorescence OLEDs, Ir(dfppy) 2 (pt) exhibited a current efficiency of 19.1 cd A−1 (EQE of 10.7%), while Ir(dfppy) 2 (dfbpy) exhibited an efficiency of 24.2 cd A−1 (EQE of 11.2%). Graphical abstract Incorporation of high-triplet-energy ancillary cyclometalating ligand brings about hypsochromic shift, narrowed spectrum, and reduced intensity at long-wavelength vibronic band, resulting in improved color purity for sky-blue iridium complex phosphor. Image 1 Highlights • Two tris-cyclometalated heteroleptic iridium complexes were designed and synthesized as sky-blue phosphors. • Iridium complex with high-triplet-energy ligand exhibited better color purity in both photoluminescence and electroluminescence. • Organic light-emitting diodes were fabricated using these iridium phosphors to realize improved color purity than the famous FIrpic. [ABSTRACT FROM AUTHOR]

Intense red-emitting double perovskite Sr 3 LiSbO 6 (SLSO) phosphor materials have been prepared by doping of Eu3+ rare earth ion using the facile solid-state reaction route. The obtained results displayed the hexagonal structure of the sample, having space group R3c. Diffuse reflectance spectra also reflected the 3.42eV optical band gap of SLSO: 2%Eu3+ which was less than that of the pure SLSO (3.5eV), consequently showing the negative Burstein Moss effect. Photoluminescence (PL) emission spectra showed a concentration quenching effect beyond the 2mol% of Eu3+ doping concentration, indicating the involvement of dipole-dipole interaction. The lifetime of the prepared phosphor was estimated by the PL decay curve; with an average decay time of 808.6 μs. Photometric studies revealed the required lesser correlated color temperature (CCT) values (<1900K) with high color purity (CP) of 99% and Commission International de'Eclairage (CIE) coordinates were located around the red region. Drawn results demonstrated that the proposed phosphor could be a promising strong red-emitting phosphor for the white light-emitting diode (wLED) based on ultra-violet UV or blue chip. [ABSTRACT FROM AUTHOR]

Exploring for red-emitting phosphor materials with supper property plays a key role in the development of white light-emitting diodes (WLEDs). Simultaneously, the crystal structure has a crucial effect on its luminescence properties. In this work, we synthesized a type of new red-emitting Li 4 Ca 2 B 8 O 16 : Eu3+ phosphor via the solid-state reaction. The phase purity, crystal structure, surface morphology, decay behavior, thermal stability, the correspondence between local symmetry and luminescence properties were investigated in detail. Under the optimal 393 nm excitation, Li 4 Ca 2 B 8 O 16 : 0.33Eu3+ shows a strong red emission located at 612 nm ascribed to the 5D 0 →7F 2 transition of Eu3+. The calculated Judd-Ofelt parameters (Ω 2 and Ω 4) have clarified that Eu3+ has lower symmetry without an inversion center, resulting in the high value of R/O (the emission intensity ratio of 5D 0 →7F 2 to 5D 0 →7F 1) of 7.95 at x = 0.33 mol. The Li 4 Ca 2 B 8 O 16 : 0.33Eu3+ phosphor exhibits a high color purity of 94.99% with the chromaticity coordinates of (0.6547, 0.3449), perfect internal quantum efficiency (99.75%) and excellent thermal stability at high temperature (90.91% at 150 °C). The results indicate that this new Li 4 Ca 2 B 8 O 16 : Eu3+ phosphor can be used as the potential red component for pc-WLEDs. [Display omitted] • A series of new red-emitting Eu3+ doped Li 4 Ca 2 B 8 O 16 phosphors have been synthesized. • The incorporation of more Eu3+ ions leads to lower structural coordinated symmetry and higher color purity. • The Li 4 Ca 2 B 8 O 16 :0.33Eu3+ owns a high color purity of 94.99% and CIE of (0.6547, 0.3449). • Compared with the emission intensity at 25 °C, the overall emission intensity still remains 90.91% at 150 °C. [ABSTRACT FROM AUTHOR]

The design and synthesis of organic materials with a narrow emission band in the longer wavelength region beyond 510 nm remain a great challenge. For constructing narrowband green emitters, we propose a unique molecular design strategy based on frontier molecular orbital engineering (FMOE), which can integrate the advantages of a twisted donor–acceptor (D‐A) structure and a multiple resonance (MR) delayed fluorescence skeleton. Attaching an auxiliary donor to a MR skeleton leads to a novel molecule with twisted D‐A and MR structure characteristics. Importantly, a remarkable red‐shift of the emission maximum and a narrowband spectrum are achieved simultaneously. The target molecule has been employed as an emitter to fabricate green organic light‐emitting diodes (OLEDs) with Commission Internationale de L'Eclairage (CIE) coordinates of (0.23, 0.69) and a maximum external quantum efficiency (EQE) of 27.0 %. [ABSTRACT FROM AUTHOR]

To extract the confined waveguided light in organic light-emitting diodes (OLEDs), inserting a low refractive index (RI) periodic structure between the anode and organic layer has been widely investigated as a promising technology. However, the periodic-structure-based light extraction applied inside devices has been shown to severely distort spectrum and affect EL characteristics. In this study, a simple light extraction technology using periodic low-RI nanodot array (NDA) as internal light extraction layer has been demonstrated. The NDA was fabricated simply via laser interference lithography (LIL). The structural parameters of periodic pattern, distance, and height were easily controlled by the LIL process. From computational analysis using finite-difference time-domain (FDTD) method, the NDA with 300 nm pitch and 0.3 coverage ratio per unit cell with 60 nm height showed the highest enhancement with spectral-distortion-minimized characteristics. Through both computational and experimental systematic analysis on the structural parameters of low-RI NDA-embedded OLEDs, highly efficient OLEDs have been fabricated. Finally, as representative indicators, hexagonal and rectangular positioned NDA-embedded OLEDs showed highly improved external quantum efficiencies of 2.44 (+29.55%) and 2.77 (+57.38%), respectively. Furthermore, the disadvantage originating from the nanoscale surface roughness on the transparent conductive oxide was minimized. [ABSTRACT FROM AUTHOR]

We report enhanced color purity of hybrid organic-inorganic light emitting diode based on polyfluorene-CdSe/ZnS quanum dot (QD) blend as emissive layer. Effect on structural, optical and electrical properties of different doping concentration (0–100 wt.%) of QD in polyfluorene (PFO) was studied. Photoluminescence and electroluminescence spectra confirm the β-formation of PFO by incorporation of CdSe/ZnS QD. Photoluminescence (PL) of blend film was also compared with another method based on one dimensional photonic band gap (1D-PBG) structure that has been used for color purity. In both the cases, that is, QD doped device and 1D-PBG based structures the narrowing of PL spectra was observed. But the fabrication of QD-doped device for color purity is easier than fabricating 1D-PBG structure using multilayer dielectric coating. The present study might find application for QD based color displays, where color purity is an important requirement. [ABSTRACT FROM AUTHOR]

This paper describes a red dopant material, the cyanocoumarin derivative 9-cyano-10-(2- benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H, I 1H-benzo [1] pyrano[6,7,8-i j]quinolizin-1 I-one (RC545T), and its use in organic light-emitting diodes (OLEDs). Because RC545T exhibits (i) redshifted fluorescence (λmax = 607 nm) and (ii) a narrower full width at half-maximum (fwhm; 48 nm) relative to the corresponding signal for 4-(dicyanomethylene)- 2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB; λmax = 605 nm; fwhm = 73 nm), which is currently one of the most efficient red dopant materials, we could fabricate red OLEDs exhibiting improved color purity. A device incorporating RC545T as a dopant and rubrene as an assistant dopant in the configuration indium-tin oxide (ITO)/N,N'-bis(1-naphthyl)- N,N'-diphenyl-1, 1'-biphenyl-4,4'-diamine (65 nm)/tris(8-hydroxyquinoline)aluminum (Alq3): 15 wt % rubrene:2 wt % RC545T (30 nm)/A1q3 (30 nm)/LiF (0.8 nm)/Al (250 nm) exhibited a maximum luminance of 8000 cd/m² at 12.5 V, with near-saturated CtE coordinates of (0.64, 0.35), significantly better red color purity than that of the device featuring DCJTB as the dopant material [CIE coordinates: (0.63, 0.37)], thereby rendering RC545T a good red-emitting dopant for OLED applications. [ABSTRACT FROM AUTHOR]

Due to the limited molecular design strategy, the development of ultrahigh color purity deep blue aggregation-induced emission (AIE) emitters with excellent photophysical and electroluminescence performances is still facing challenges at present. In this study, an effective design strategy for deep blue emitters is proposed, which can improve the performances of non-doped organic light-emitting diodes (OLEDs) by adjusting the link mode of the phenyl bridge and utilizing the steric hindrance effect of the rigid plane. Two new emitters, 3BCzPT and 4BCzPT, were obtained with phenanthroline acceptor and carbazole donor for deep blue emitting OLEDs. Particularly, 3BCzPT has been proven to have AIE characteristics through photophysical properties. Non-doped OLEDs with 3BCzPT demonstrate prominent electroluminescence (EL) performances reaching a maximum current efficiency (CEmax) of 6.3 cd A−1 and maximum external quantum efficiency (EQEmax) of 3.81%, well as ultrahigh color purity with Commission Internationale de L'Eclairage (CIE) coordinates of (0.151, 0.053). While the parameters of non-doped OLED based 4BCzPT are 4.2 cd A−1, 1.96% and (0.147, 0.082). Both emitters exhibit narrow EL spectra with the full-width at half maximum (FWHM) of 56 and 52 nm. • A strategy to construct deep blue AIE emitters with D-π-A-π-D configuration was proposed. • Highly twisted configurations are beneficial to the formation of weak intra/intermolecular interaction. • Non-doped OLEDs provided ultrapure deep blue emission with CIE x ≤0.15 and CIE y ≤0.08. • This feasible strategy can enrich the design strategy of deep blue emitters and further extend their application in OLEDs. [ABSTRACT FROM AUTHOR]

This paper demonstrates how sensitizer doping improves the color purity and emission stability of a red organic light-emitting diode (OLED). A device with an MADN-Alq3 co-host emission layer was fabricated. From electroluminescence (EL) measurements, it was found not only that the residual emission from Alq3 affected the emission color and emission stability of the device but also that the residual Alq3 emission was reduced by the addition of Rubrene and C6 sensitizers. Rubrene doping increased both the luminance intensity and current density of the device by a factor of 2.0, whereas C6 doping increased the luminance intensity by a factor of 1.3 and the current density by a factor of 1.2. When the current density was increased from 10 to 132 mA/cm2, the decrease in EL efficiency was less than 10.8%. The variations (Δx, Δy) in the CIE coordinates were (0.02, 0.01) for the device doped with Rubrene and (0.01, 0.01) for that doped with C6. The maximum EL efficiency was 5.28 cd/A, and the CIE coordinates were (0.63, 0.36). [ABSTRACT FROM AUTHOR]

In this study, the optimal structure for obtaining high green color purity was investigated by modeling quantum dot (QD)–organic light-emitting diodes (OLED). It was found that even if the green quantum dot (G-QD) density in the G-QD layer was 30%, the full width at half maximum (FWHM) in the green wavelength band could be minimized to achieve a sharp emission spectrum, but it was difficult to completely block the blue light leakage with the G-QD layer alone. This blue light leakage problem was solved by stacking a green color filter (G-CF) layer on top of the G-QD layer. When G-CF thickness 5 μm was stacked, blue light leakage was blocked completely, and the FWHM of the emission spectrum in the green wavelength band was minimized, resulting in high green color purity. It is expected that the overall color gamut of QD-OLED can be improved by optimizing the device that shows such excellent green color purity. [ABSTRACT FROM AUTHOR]

In the surge of new inorganic luminescent host for lanthanide ion for efficient solid-state lighting, Ln 2 TiO 5 comes as a new class of materials with all optically suited properties. Triggered by very high solubility of Eu3+ ion in Gd 2 TiO 5 with minimal lattice strain, negligible doping induced structural distortion and no charge compensating defects; Gd 2 TiO 5 :Eu3+ (GTOE) delivered an extraordinary credentials as novel phosphor material. GTOE demonstrated no concentration quenching up to 10 mol % doping; monotonic rise in emission intensity, higher excited state lifetime, high red color purity∼99% and PLQY∼ 14%. Luminescence lifetime spectroscopy suggested stabilization of Eu3+ in both GdO 7 with distorted pentagonal bipyramid (DPB) and distorted hexagonal bipyramid (DHB) geometry having similar coordination and symmetry and is well supported by two stark components in 5D 0 →7F 0 transitions. Positron annhilation lifetime spectroscopy (PALS) suggested that average positron lifetime remained constant in all the samples indicating no charge compensating defects formation further justifying occupancy of Eu3+ in isovalent Gd3+ site. Judd-Ofelt analysis suggested that local symmetry around Eu3+ ion and polarizability of Eu–O bonds in GTO host doesn't change throughout the concentration range. This work proposed an excellent candidate for red emitting materials towards phosphor converted white light emitting diodes (pcLEDs) having high dopant solubility, PLQY and color purity. [Display omitted] • New Phosphor Gd 2 TiO 5 :Eu3+ (GTOE) for efficient, narrow and pure red emission is designed. • Complete Europium solubility in GTOE distributed at both distorted pentagonal and hexagonal bipyramid GdO 7. • GTOE demonstrated no fluorescence quenching up to 10 mol %, absolute PLQY∼14% and color purity ∼99%. • Positron lifetime suggested formation of vacancy aggregates at the expense of smaller vacancies with Eu3+ doping. • Eu3+ local symmetry and Eu–O bond polarizability doesn't change up to 10 mol %. [ABSTRACT FROM AUTHOR]

CH 3 NH 3 PbCl 3 (MAPbCl 3) light emitting diodes (LEDs) with emission in deep-blue were demonstrated with an areal dimension of 3.5 mm by 3.5 mm. An inverted p-i-n diode structure consisted of ITO/PEDOT:PSS/MAPbCl 3 /TPBi/LiF/Al with bulk MAPbCl 3 thin film as the emission layer was synthesized via combined thermal deposition, spin-coating, and anti-solvent treatment techniques. The perovskite film was authenticated by X-ray diffraction, scanning electron microscopy, and atom force microscopy and exhibited high in crystallinity and morphology. The energy level alignments between layers were determined by the UPS technique. The device displayed a diode behavior with a turn-on voltage of approximately 3.2 V and a saturation current density of 118 mA/cm2. Under forward bias, the emission of LEDs was centered at 408.8 nm with a full width at half maximum of only 7 nm, a color purity of 97% and an CIE coordinate of (0.16, 0.036), respectively. The optimum external quantum efficiency and luminance of 0.036% and 37 cd/m2 were achieved at current density of approximately 90 mA/cm2 and 118 mA/cm2 at room temperature, respectively. To our best knowledge, this investigation first realized bulk perovskite LEDs with the shortest emission wavelength and the highest color purity in deep-blue. [Display omitted] • Deep-blue MAPbCl 3 bulk thin film LED with an aerial size over 12 mm2. • Electroluminescence with a FWHM of only 7 nm and a color purity of 97%. • Short center emission wavelength at 408.8 nm. • Preparation method in favorable for making large-area display and lighting device. [ABSTRACT FROM AUTHOR]

Novel red-emitting phosphors, Sr 3 LaTa 3 O 12 :Eu3+ (SLTO:Eu3+), have been successfully synthesized for use in white light-emitting diodes (w-LEDs) and latent fingerprint (LFP) visualization applications. The crystalline structure, bandgap, and photoluminescence (PL) of the SLTO:Eu3+ phosphors were thoroughly investigated. Under 395 nm excitation, SLTO:Eu3+ phosphors emitted orange-red light at the wavelength of 616 nm due to the 5D 0 -7F 2 transition of Eu3+ ions. The optimal doping concentration of the phosphor is x = 0.30 and the neighbor ions interaction is the most critical factor in the concentration quenching mechanism of the SLTO:Eu3+ phosphor. Furthermore, the SLTO:0.30Eu3+ phosphor exhibit higher thermal stability compared to the conventional red phosphor (Sr 2 Si 5 N 8 :Eu2+). The packaged w-LED showed a correlated color temperature (6887 K), excellent color rendering index (95), and Commission International de l'Eclairage (CIE) coordinates of (0.305, 0.334). The SLTO:0.30Eu3+ phosphor effectively detected level 1–3 structures of LFPs under ultraviolet irradiation, and ultimately detected LFPs in various daily life circumstances. These findings indicate that the SLTO:0.30Eu3+ phosphor might be a viable option for w-LED lighting applications and LFPs visualization. • Sr 3 LaTa 3 O 12 :Eu3+ phosphors are firstly synthesized via solid-state reaction. • The phosphor emits bright red light excited by 395 nm. • The phosphor exhibits good thermal stability and high color purity. • Sr 3 LaTa 3 O 12 :Eu3+ phosphors has potential to be used for w-LED application and LFPs visualization. [ABSTRACT FROM AUTHOR]

A series of Eu 3+ -activated Na 2 Gd(PO 4 )(MoO 4 ) red-emitting phosphors were prepared by a facile high-temperature solid-state reaction method. The synthesized samples were characterized by X-ray diffraction, field-emission scanning electron microscope, photoluminescence (PL) spectra, luminescence decay curves and temperature-dependent emission spectra. Under the excitation of 396 nm, the resultant samples exhibited the characteristic emissions of Eu 3+ ions corresponding to the 5 D 0 → 7 F J transitions. The optimal doping concentration of Eu 3+ ions was determined to be 50 mol%. The critical distance was around 8.98 Å and the concentration quenching was dominated by quadrupole-quadrupole interaction. Furthermore, the prepared samples also possessed good color coordinate (0.653, 0.346) and high color purity of 92%. The temperature-dependent PL spectra suggested that the resultant products possessed good thermal stability and the activation energy was found to be 0.22 eV. Additionally, the internal quantum efficiency and the external quantum efficiency of the phosphors was measured to be 90% and 37%, respectively. These results demonstrated that the Eu 3+ -activated Na 2 Gd(PO 4 )(MoO 4 ) phosphors are very appropriate red-emitting phosphors for applications in near-ultraviolet-excited white LEDs. [ABSTRACT FROM AUTHOR]

In recent years, rare-earth-based phosphors for near-ultraviolet (NUV)-triggered white light emitting diodes (w-LEDs) have become a research hotspot. However, it is still not possible to obtain phosphors with high quantum yield, excellent color purity and multiple applications. Hence, a series of novel Eu3+-activated Ca3Ga2Ge4O14 (CGG) red-emitting phosphors with high quantum efficiency, excellent color purity and good thermal stability were prepared by a high-temperature solid-phase method. All the CGG:Eu3+ phosphors emitted dazzling red emission with excitation at 394 nm. The optimal Eu3+ doping concentration of compounds was 12% with an excellent color purity of 97.89%, and the concentration quenching mechanism was investigated as dipole–dipole interactions. Meanwhile, the synthetic samples exhibited good thermal stability with the activation energy of 0.26 eV. Remarkably, the internal quantum yield of the prepared phosphors reaches 94.26%. Furthermore, the emission spectra of the prepared red-LEDs overlap considerably with the absorption spectra of PR and PFR required for plant growth. The w-LED device emits warm white light with a high color rendering index of 91.64 and an appropriate correlated color temperature of 4808 K. These excellent luminescence properties indicate that the prepared CGG:Eu3+ phosphors exhibit extensive potential for applications in plant growth lighting and white LEDs. [ABSTRACT FROM AUTHOR]

An excellent light-emitting diodes phosphor must possess effective absorption, high quantum efficiency, high quenching temperatures, and high color purity. Our synthesized LiGd(WO4)2:Eu3+ materials possess all of these properties. Excitation of these phosphors with ultraviolet radiation yields bright red emission at 617 nm due to the 5D0→7F2 transition of Eu3+ ions. Compared with different Eu3+ doping concentrations, LiGd(WO4)2:80%Eu3+ phosphor has optimal photoluminescence properties and shows internal quantum efficiency as high as 69%. More impressive is its good thermal stability; when heated up to 150 °C, the LiGd(WO4)2:80%Eu3+ phosphor still has 81% of its initial emission intensity at room temperature. Furthermore, the LiGd(WO4)2:80%Eu3+ phosphor shows high purity of red emission with coordinate values (x = 0.656, y = 0.334). The abovementioned results suggest that the LiGd(WO4)2:80%Eu3+ phosphor can be a suitable red-emitting candidate for ultraviolet-excited white light-emitting diodes. [ABSTRACT FROM AUTHOR]