Search

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]

Organic light‐emitting diodes (OLEDs) based on multiple resonance‐thermally activated delayed fluorescence (MR‐TADF) have the advantages of high exciton utilization and excellent color purity. However, the large conjugated planarity of general MR‐TADF emitters makes them easily aggregate in the form of π–π stacking, resulting in aggregation‐caused quenching (ACQ) and the formation of excimers, which reduce exciton utilization efficiency and color purity. To address these issues, large shielding units can be incorporated to prevent interchromophore interactions, whereas the majority of reported molecules are limited to blue‐green light emissions. This work proposes a strategy of incorporating steric hindrance groups at different sites of the B/N core to suppress interactions between chromophore, contributing to blue MR‐TADF emitters with high photo‐luminance quantum yields (PLQYs ≥ 95%) and narrow full width at half maximum (FWHM), and importantly, great suppression of the ACQ effect. Therefore, blue OLEDs achieve high external quantum efficiencies up to 34.3% and high color purity with FWHM of about 27 nm and CIE around (0.12, 0.15), even at a high doping concentration of 20 wt%. [ABSTRACT FROM AUTHOR]

Abstract Organic light‐emitting diodes (OLEDs) based on multiple resonance‐thermally activated delayed fluorescence (MR‐TADF) have the advantages of high exciton utilization and excellent color purity. However, the large conjugated planarity of general MR‐TADF emitters makes them easily aggregate in the form of π–π stacking, resulting in aggregation‐caused quenching (ACQ) and the formation of excimers, which reduce exciton utilization efficiency and color purity. To address these issues, large shielding units can be incorporated to prevent interchromophore interactions, whereas the majority of reported molecules are limited to blue‐green light emissions. This work proposes a strategy of incorporating steric hindrance groups at different sites of the B/N core to suppress interactions between chromophore, contributing to blue MR‐TADF emitters with high photo‐luminance quantum yields (PLQYs ≥ 95%) and narrow full width at half maximum (FWHM), and importantly, great suppression of the ACQ effect. Therefore, blue OLEDs achieve high external quantum efficiencies up to 34.3% and high color purity with FWHM of about 27 nm and CIE around (0.12, 0.15), even at a high doping concentration of 20 wt%.

We have studied the optical and luminescence properties at room temperature of ultrathin colloidal semiconductor cadmium selenide nanoscrolls with a thickness of 2.5 monolayers. For colloidal synthesis of the objects under study, cadmium acetate dihydrate Cd(CH3COO)2·2H2O and trioctylphosphine selenide were used as precursors of cadmium and selenium, respectively, and solutions of oleic acid and octadecene were also used. Luminescence spectrum of cadmium selenide nanoscrolls was recorded using a fiber charge coupled device spectrometer. Spectrally resolved photoluminescence decays for nanoparticles were measured with the use of time-correlated single photon counting technique. The emission of the cadmium selenide nanoscrolls consists of interband and recombination luminescence bands. We found that the normalized photon numbers of recombination luminescence are larger than the normalized photon numbers of interband luminescence. We determined dominant wavelengths, chromaticity coordinates, and correlated color temperatures of ultrathin colloidal semiconductor cadmium selenide nanoscrolls. These ultrathin cadmium selenide nanoscrolls are promising for application in light-emitting diodes.

In this research, the effects of solvent type, solvent to seed ratio, temperature and time of extraction on the yield, the color purity and the yield of bixin/norbixin of annatto were studied. Central Composite Design with 4 parameters including of solvent type (acetone, NaOH and acetone-NaOH), solvent to seed ratio (1:1 to 5:1 ml/g), time (2-6 h) and temperature of extraction (25-65 ºC) in three levels (-1, 0 and +1) was employed. The results indicated that the quadratic model was significant for the yield of annatto and R2 = 0.915, indicating that 91.5 % of the change in the responses could be predicted by the fitted model. In addition, the temperature and time of extraction had no any significant effect on the extraction yield. The maximum yield was predicted by NaOH under the 46.41 ºC, 2.05 h and solvent to seed ratio of 5:1, which was 13.31 %. The quadratic model was significant for the color purity of annatto and R2 = 0.848. By changing the solvent from acetone to NaOH and increasing the solvent to seed ratio, the color purity increased. Furthermore, bixin/ norbixin yield, which is the weight ratio of bixin or norbixin to annatto seed, was determined and calculates as a comprehensive response. The most effective factor in the color change of annatto powder was determined as light and if it removed, using suitable packaging, it would be possible to maintain the best quality of the powder .Similar results were obtained regarding the stability of annatto dye in the whey powder. [ABSTRACT FROM AUTHOR]

• Ultrathin silica shells enhance PNC stability, enabling straightforward introduction in ML platforms. • Achieved superior color purity with a narrow FWHM of 32 nm for advanced ML applications. • Demonstrated high durability of PMP film under extreme conditions. The quest for advanced mechanoluminescence (ML) systems with precise color control and a broad color gamut is pivotal for developing flexible display technologies. Despite significant progress in embedding ML phosphors into elastic polymer matrices to enhance flexibility and resilience, achieving high color purity and a broad color spectrum remains a substantial challenge. This study introduces an innovative approach by incorporating ultrathin silica-encapsulated perovskite nanocrystals (PNCs) into the ML platform, leveraging their exceptional color purity and high photoluminescence quantum yield. Our encapsulation technique, which covers PNCs with SiO 2 shells, not only enhances the environmental stability of PNCs but also enables their integration into a polydimethylsiloxane (PDMS)-based ML matrix, thereby forming a robust perovskite mechanoluminescence platform (PMP) film. This strategy significantly improves ML color purity with a full width at half maximum (FWHM) of 32 nm, as well as leading to high ML stability in various harsh conditions such as heating and water immersion. Our findings demonstrate the potential of silica-encapsulated PNCs to transcend the conventional limitations of ML systems, marking a significant stride towards the realization of advanced flexible displays with superior color purity. [ABSTRACT FROM AUTHOR]

Abstract A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. Graphical Abstract

ZnO and cerium-doped ZnO on a glass substrate have been prepared by the sol–gel method using the spin coating technique and water bath growth process. Ce-doping concentration on film structure, morphology, and optical properties is investigated. The result indicated that the hexagonal wurtzite ZnO with high crystalline quality formed on the substrate. The crystal parameters a and c decreased, crystal size increased, and the compressive strain formed after Ce-doping. Formed un-, 3%, 6%, 12% Ce-doped ZnO film has a spherical shape with a size between 8.6–31, 14–52, 18–56, and 20–91 nm, respectively. All films had good absorption of 300–400 nm ultraviolet light, in particular, the absorption of near ultraviolet (370–400 nm) increased after doping of Ce. The transmittance of light between 400–800 nm decreased with Ce-doping concentration. The band gap energy increased after Ce-doping reaching better optical behavior for preparing ZnO heterostructured thin-film. All film emitted intense blue emission under 375 nm excitation at room temperature. This indicated the film can have application in optoelectronic devices. [ABSTRACT FROM AUTHOR]

A series of Sm3+-activated Ca 3 Gd(AlO) 3 (BO 3) 4 red-emitting phosphors were prepared by a traditional high-temperature solid-state approach. They were characterized by XRD refinements, TEM, SEM, EDS, DRS, FTIR, Raman spectra, photoluminescence (PL) spectra, and fluorescence decay curves. The microstructure of the cation-borate phosphors and the presence of Sm3+ dopants, and their impact at the Ca and Gd sites were studied. All the samples exhibited bright red emissions caused by intra-4f transitions of Sm3+ ions when excited at 404 nm. The optimum dopant concentration was 4mol%, and the concentration quenching (CQ) process was driven by dipole-dipole interaction using Inokuti-Hirayama, and Dexter theories. Interestingly, the temperature-dependent PL spectra manifested that the resulting phosphor had excellent thermal stability with an activation energy of 0.234 eV. Ultimately, the investigated phosphor demonstrated excellent chemical stability. The Sm3+-doped CGAB:Sm3+ phosphor can convert NUV LED chips into intense red emission with Commission Internationale de l'Eclairage (CIE) diagrams of 0.615, 0.382 and high color purity of up to 95.6%. The WLED containing CG 0.96 AB:0.04Sm3+ merged with the commercial phosphors revealed low correlated color temperature (CCT≈4197 K) and high color rendering index (CRI≈89.7). EL spectrum of the fabricated Red-LED device. Inset exemplifies the coordination diagram and image for the red phosphor. UV excitation induced bright red emissions with high color purity and outstanding thermal-quenching (TQ) resistance. Luminescent pictures of the prepared Red–LED and White-LEDs device with the input current.▪ • UV excitation induced bright red emissions with high color purity up to 95.6%. • They possessed good chemical stability in an existing environment. • The CG 0.96 AB:0.04Sm3+ exhibited outstanding thermal-quenching (TQ) resistance of>90.8%. • Red LED and WLED devices were fabricated by using phosphor and UV LED chips. [ABSTRACT FROM AUTHOR]

A common full-color method involves combining micro-light-emitting diodes (LEDs) chips with color conversion materials such as quantum dots (QDs) to achieve full color. However, during color conversion between micro-LEDs and QDs, QDs cannot completely absorb incident wavelengths cause the emission wavelengths that including incident wavelengths and converted wavelength through QDs, which compromises color purity. The present paper proposes the use of a recycling-reflection color-purity-enhancement film (RCPEF) to reflect the incident wavelength multiple times and, consequently, prevent wavelength mixing after QDs conversion. This RCPEF only allows the light of a specific wavelength to pass through it, exciting blue light is reflected back to the red and green QDs layer. The prototype experiment indicated that with an excitation light source wavelength of 445.5 nm, the use of green QDs and RCPEFs increased color purity from 77.2% to 97.49% and light conversion efficiency by 1.97 times and the use of red QDs and RCPEFs increased color purity to 94.68% and light conversion efficiency by 1.46 times. Thus, high efficiency and color purity were achieved for micro-LEDs displays. [ABSTRACT FROM AUTHOR]

Herein, we designed Er3+-incorporated zincate-based nanomaterials via a rapid, low-cost, and environmentally friendly urea-combustion route. X-ray powder diffraction (XRPD) profiles revealed their orthogonal crystalline structure. Electron microscopy showed nanoscale (48–70 nm) non-uniform agglomerated particles. The presence of [BaO11] and [ZnO5] structural units in the present samples was shown by Fourier-transform infrared (FT-IR) spectroscopy. Emission spectra yielded a characteristic peak at 551 nm, which contributed to their bright-green light. The optimal nanomaterial had 3.0 mol% of Er3+ content, and it exhibited excellent bright-green light. Exchange-type multipolar inter-linkages via cross-relaxation predominantly direct the quenching of luminescence post x = 0.03 Er3+ content, as shown by the Inokuti-Hirayama (I-H) model. The optical bandgap and Urbach energy were obtained from experimental data-fitting with Tauc's hypothesis and an empirical correlation. Excellent color-purity (87.86%) and color temperature (6916 K) with chromaticity coordinates (0.2531, 0.6106) of the optimized nanomaterial were similar to National Television Standards Committee (NTSC) and NICHIA Corporation fabricated light-emitting diode (LED) green standards. Hence, the developed nanomaterials appear to be a good candidates for generating cool-green light in high-performance blue/green/red (B/G/R) white-light-emitting diodes (wLEDs), sensors, and laser applications. [ABSTRACT FROM AUTHOR]

Oxyfluoride (P2O5-Bi2O3-Na2CO3-SrCO3-ZnF2-Eu2O3) glasses of different dopant (Eu3+) ion concentrations were synthesized by the traditional melt quenching method. Optical absorption, luminescence and lifetime measurements were performed with UV-Vis and PL techniques. A total of six absorption bands were observed in the wavelength range 200-800 nm, including one intense high band at 392 nm was assigned to 7F0→5L6 transition. The covalency between the host environment and Eu3+ ion was noticed with the measured nephelauxetic ratios (β) and bonding parameters (δ). The energies of the energy band gaps (Eg) and Urbach (ΔE) were estimated from the Tauc's plots, drawn from the absorption spectra. Luminescence spectra exhibited the prominent reddish-orange emission at 612 nm due to the 5D0→7F2 characteristic transition of Eu3+ ion. The lasing (radiative) parameters of f-f transitions of the Eu3+ ion was evaluated using the Judd-Ofelt intensity parameters (Ω2, Ω4, and Ω6). The higher magnitude of branching ratios (βexp) suggests the suitability of the present glass. The decay profile for the 5D0 level of europium was recorded by monitoring the emission and excitation wavelengths 612 & 392 nm, respectively. The color temperature and purity were calculated using CIE 1931 color coordinates. The emission color band spectra have also been recorded. [ABSTRACT FROM AUTHOR]

Herein, the novel white light-emitting diode (WLED) structures based on the Ca 2 Y(Nb,Sb)O 6 :Mn4+ materials were presented. The crystal structure, morphology, elemental composition, luminescent behavior, thermal stability, quantum yield, decay curve, and color purity of Ca 2 YSbO 6 :Mn4+ (CYS:Mn4+) and Ca 2 YNbO 6 :Mn4+ (CYN:Mn4+) phosphors were investigated and compared in detail. For these phosphors, the concentration quenching (CQ) mechanism is different. For CYS:Mn4+ phosphors, the dipole-dipole interaction dominates the CQ while the dipole-quadrupole interaction is dominant in CYN:Mn4+ phosphors. The emission intensity of the optimal CYN:Mn4+ phosphors was stronger than that of the CYS:Mn4+ phosphors. Meanwhile, the color purities of the optimal CYS:0.003Mn4+ and CYN:0.003Mn4+ phosphors were calculated to be as high as 96.40% and 96.91%, respectively. Eventually, it is interesting that the packaged novel WLED structure would improve the color rendering index and correlated color temperature values. From the above results, non-rare-earth Ca 2 Y(Nb,Sb)O 6 :Mn4+ materials with high color purities could be proposed for WLED devices. [ABSTRACT FROM AUTHOR]

Multi-resonance thermally activated delayed fluorescence (MR-TADF) materials, based on polycyclic aromatic frameworks, have shown promise in achieving narrow-band emission and high luminous efficiency. In this study, we investigate the performance of a blue MR-TADF material, 2′2'2''-(1,3,5-triazine-2,4,6-triyl) tris(9-(2-(naphthalen-2-yl)phenyl)-9H-carbazole) (TBN-TPA), in tandem OLED devices. Single emitter unit and two emitter unit tandem OLED devices with blue MR-TADF material were explored with optical modeling simulation. More importantly, the tandem architecture assists in realizing narrow-band emission and high color purity via optical interference and microcavity effects, which are essential for meeting BT 2020 standards. TBN-TPA achieves narrow full width at half maximum down to 24 nm and CIE coordinates approaching the blue region in tandem devices. Our work highlights the significant advantages of combining tandem architectures and emerging MR-TADF emitters for developing high-performance OLEDs with both high efficiency and wide color gamut. This is the first demonstration of using tandem OLED architecture to improve both efficiency and color purity of a blue multi-resonance TADF emitter. Further research on optimizing tandem structures and designing advanced MR-TADF materials will promote the applications of OLED displays. • Single-emissive and dual-emissive layer blue MR-TADF tandem OLED devices were explored with optical modeling simulation. • The tandem architecture assists in realizing narrow-band emission and high color purity via optical interference and microcavity effects with a narrow FWHM of 24 nm and CIE coordinates approaching the blue region in tandem devices. [ABSTRACT FROM AUTHOR]

Novel reddish-orange-emitting Ca 2 GdNbO 6 :Sm3+ phosphors based on the emission of 4G 5/2 → 6H 9/2 transition at 651 nm with the chromatic coordinate of (0.633, 0.366) were synthesized. The crystal structure and chemical purity were identified in detail. Under the 407 nm excitation, the optimum concentration of Sm3+ ion was found to be 5 mol% dominated by the dipole-dipole interaction in the Ca 2 GdNbO 6 host material. The color purity of the sample with optimum doping was estimated to be about 78.38%. Besides, the thermal stability was also studied, and it was further found that the emission intensity remained 65.32% at 423 K. The packaged white LED device exhibited excellent CRI and CCT values of 92.43 and 4896 K. Finally, the polydimethylsiloxane film with a stable structure and flexible property was prepared. These above results reveal that novel reddish-orange-emitting Ca 2 GdNbO 6 :Sm3+ phosphors can be applied in high CRI white communication and flexible display applications. [ABSTRACT FROM AUTHOR]

Novel cubic perovskite based orange red emissive Sr 9(1-x) Al 6 O 18 : 9 x Sm3+ (0.001 ≤ x ≥ 0.04) nanocrystals were developed by environmentally benign and low temperature urea combustion method. Phase structure analysis showed the cubic structure with Pa 3 ‾ (205) space group. Scanning and transmission electron micrographs reported the agglomerated cubic morphology of the nanoparticles ranging from 40 to 60 nm. EDS (energy dispersive X-ray analysis) outcomes traced the adequate elemental composition of the spectral materials. The prepared nanomaterials displayed the fine orange red emission via 4G 5/2 → 6H 7/2 typical transition centered at 599 nm. Optical analysis asserted the wide band gap values of Sr 8.82 Sm 0.18 Al 6 O 18 (3.77 eV) and Sr 9 Al 6 O 18 (4.08 eV). Reliance of the emission intensity of developed nanophosphors on Sm3+ concentration claimed the Sr 8.82 Sm 0.18 Al 6 O 18 as most desirable one with CIE coordinates (0.5833, 0.4159), 1747 K correlated color temperature (CCT) and color purity of 90.65%. These excellent results proved the relevancy of present nanophosphors as a novel promising material in the development of down conversion white LEDs. Also, the present research findings thus, can be well recurred to explore more about Sr 9 Al 6 O 18 based spectral nanomaterials. [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]

Colloidal nanoplatelets (NPLs) are a kind of two-dimensional nano-material with an atomically flat surface, leading to an ultra-narrow emission linewidth of 8~12 nm. In this article, we fabricated green light-emitting diodes (LEDs) based on CdSe/CdS core/crown NPLs. This device exhibited an electroluminescence (EL) at 521 nm with a full-width at half maximum (FWHM) of 15 nm and a maximum luminance of 4684 cd/m2. Such narrow EL FWHM indicates that the core/crown NPLs can achieve an ultrapure green LED with 124.7% of National Televison System Committee (NTSC), realizing a high color saturation and wide color gamut display. [ABSTRACT FROM AUTHOR]

In this work, by combining conformational isomeric moiety to MR-emitting core, we propose a new pathway to reduce the concentration sensitivity without compromising color purity of MR-TADF emitters. [Display omitted] • Two novel MR-TADF emitters with conformational isomerism were designed. • Conformational isomerism is introduced to deal with poor concentration dependence. • Concentration quenching can be suppressed with barely harming color purity. • BNCz-aDMAC-based OLEDs achieve superior performance with low concentration dependence. Electroluminescent performance of multiple resonance (MR) type thermally activated delayed fluorescence (TADF) emitters is highly dependent to the doping concentration due to the flat molecular structures, which is a major issue toward practical applications. Herein, an effective approach reducing the concentration dependence is proposed by introducing conformational isomerism for MR-TADF emitters. Two novel MR-TADF emitters were designed by decorating 10H-spiro[acridine-9,2′-adamantane] (a-DMAc) as a dual-conformational moiety onto the MR-core BNCz with different connection methods, which could induce different conformational distributions. In particular, the conformational isomerism of BNCz-aDMAC leads to a lower fraction of QE forms compared to the QE-dominant BNCz-PDMAC in amorphous doped film states with identical doping weights, thus enabling effective suppression of concentration quenching with barely harming color purity. Therefore, BNCz-aDMAC-based organic light-emitting diodes (OLEDs) demonstrate consistent and high efficiency over a wide doping range, maintaining a maximum external quantum efficiency of 23.8 % and a full width at half maximum of 31 nm even at a high doping ratio of 30 wt%. [ABSTRACT FROM AUTHOR]

Europium doped strontium meta-silicate (namely SrSiO3:Eu3+) phosphor was prepared by a high temperature solid state reaction method. The sintered SrSiO3:Eu3+ phosphor possesses a monoclinic structure by the XRD. Energy dispersive X-ray spectrum (EDS) confirms the presence of elements in the desired sample. Thermoluminescence (TL) kinetic parameters such as activation energy (E), order of kinetics (b), and frequency factor (s) were calculated by the peak shape method. The orange–red emission was shown to originate from the 5D0–7FJ (J = 0, 1, 2, 3, 4) transitions of Eu3+ ions as the sample was excited at 396 nm. The SrSiO3:Eu3+ phosphor with almost pure orange-red color purity (99.62%) shows the quantum efficiency of 10.2% (excited by 396 nm), which is higher than those of commercial red phosphors Y2O3:Eu3+ and Y2O2S:Eu3+ with quantum efficiencies of 9.6% (excited by 394 nm) and 4.2% (excited by 395 nm), respectively. Mechanoluminescence (ML) intensity of the SrSiO3:Eu3+ phosphor was also found to increase linearly with increasing the impact velocity of the moving piston, suggesting that the discussed phosphor can be used as a stress sensor.

CaZrO3:xEu3+ (x = 1.0, 2.0, 3.0, 4.0, and 5.0 mol%) phosphors were successfully prepared by a solid state reaction method. The crystal structure of sintered phosphors was hexagonal phase with space group of Pm-3m. The near ultra-violet (NUV) excitation, emission spectra of the CaZrO3:xEu3+ phosphors were composed of sharp line emission associated with the transitions from the excited states 5D0 to the ground state 7Fj (j = 0, 1, 2, 3, 4) of Eu3+. The results indicated that CaZrO3:xEu3+ might become an important orange-red phosphor candidate for use in white light emitting diodes (WLEDs) with near-UV LED chips. The mechanoluminescence (ML) intensity increases linearly with increasing impact velocity of the moving piston, suggesting that the sintered phosphors can also be useful as a stress sensor.

A red-emitting Eu3+-activated double perovskite Sr 3 MoO 6 phosphor material was successfully synthesized by a high-temperature solid-state reaction. Upon 353 and 467 nm excitations, the prepared phosphors exhibited the feature emission properties of Eu3+ ions with the corresponding characteristic electronic transitions. The concentration quenching of Eu3+ ions was found at 30 mol% and the quadrupole-quadrupole interaction was dominant in quenching process. The chromaticity coordinates for the optimal doping concentration of Eu3+ ions under the 353 and 467 nm excitations were in the pure red region, while the color purity was calculated to be about 94.536 and 94.780%, respectively. The superior luminescence properties of the red-emitting Sr 3 MoO 6 :0.3Eu3+ phosphor were achieved and with further blending with commercial phosphors, the white light-emitting diode (WLED) devices were fabricated for practical application. The fabricated WLED device based on 385 nm near-ultraviolet (NUV) chip revealed the color-rendering index and color temperature values of 90.96 and 6381 K, respectively. And the soft polydimethylsiloxane film emitted the pure red region under NUV light. These results suggest that this kind of material could be a promising red-emitting phosphor for WLEDs and flexible display film. [ABSTRACT FROM AUTHOR]

Abstract We report, synthesis of orange red light emitting Sm3+ activated BiOCl phosphors at relatively low temperature (400 °C) and shorter duration of 1 h. Rietveld refined results confirmed that all the compounds crystallized in the tetragonal structure with space group P 4/ nmm (No. 129). Functional group analysis were carried out by Fourier transform infrared (FT-IR) and Raman spectroscopy. The Photo-luminescent (PL) experiment results reveal that, an intense PL transition at 598 nm (4G 5/2 → 6H 7/2) corresponds to orange red emission at λ ex = 408 nm. The maximum emission intensity was observed for BiOCl: Sm3+ (3 mol%) phosphor, above this concentration quenching takes place due to charge exchange with neighboring Sm3+ ions. Time resolved fluorescence spectroscopic result reveals that, the decay curve is bi-exponential in nature and having long lifetime (τ = 0.58 ms). The obtained CIE and CCT values suggest that these phosphors having excellent color purity (∼90%) and low correlated color temperature. These results suggest that, Sm3+ activated BiOCl can be a potential red phosphor materials for WLEDs and other optoelectronics applications. Highlights • Series of Sm3+ ions activated BiOCl phosphors were synthesised by the solid state method. • Concentration dependent PL and quenching effects of Bi 1-x Sm x OCl phosphors were determined. • CIE, CCT, color purity, quantum efficiency and other spectroscopic properties have been evaluated. • These orange red phosphors can act as a promising candidate for opto-electronic and WLEDs applications. [ABSTRACT FROM AUTHOR]

The structure of indium tin oxide (ITO) (100 nm)/molybdenum trioxide (MoO3) (15 nm)/N,N0-bis-(1-naphthyl)-N,N0-biphenyl-1,10-biphenyl-4,40-diamine (NPB) (40 nm)/4,4'-bis(2,2- diphenylvinyl)-1,1'-biphenyl (DPVBi) (10 nm)/5,6,11,12-tetraphenylnaphthacene (rubrene) (0.2 nm)/DPVBi (24 nm)/rubrene (0.2 nm)/DPVBi (6 nm)/4,7-diphenyl-1,10-phenanthroline (BPhen):cesium carbonate (Cs2Co3) (10 nm)/Mg:Ag (6 nm)/Al (120 nm) white organic lightemitting diode (WOLED) with high color purity and stability was fabricated. The function of the multiple-ultrathin material (MUTM), such as rubrene, is as the yellow light-emitting layer and trapping layer. The results show that the MUTM has excellent carrier capture effect, resulting in high color stability of the device at different applied voltages. The Commission Internationale De L'Eclairage (CIE) coordinate of this device at 3-7 V shows a few displacements and a very slight variation of (±0.01, ±0.01). The maximum brightness of 9986 cd/m² and CIE coordinates of (0.346, 0.339) are obtained at 7 V. The enhanced performance of the device may result from the direct charge trapping in MUTM, and it can be found in the electroluminescence (EL) process. [ABSTRACT FROM AUTHOR]

Abstract Carbon-nitride multilayer systems were synthetized on silicon substrates by r.f. magnetron sputtering with alternatively changing the sputtering plasma composition between pure Ti+C and Nb elements under a reactive mixture of Ar/N 2. Bilayer numbers were increased from nanometric range (15 nm) to higher micrometric range (1.5 μm). The structural and chemical properties were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (TEM), Electron energy loss spectroscopy (EELS) and optical properties via color purity. The multilayer period effect on the optical properties such as color purity was studied and the color dependence as function of bilayer number with niobium (Nb) modulation in the TiCN/TiNbCN system determined. The spectra for all layers showed high reflectances at large wavelengths, e.g. 92% for the TiNbCN layer, 89% for the TiCN layer and about 75% for the TiCN/TiNbCN multilayer deposited with n = 200, Λ = 15 nm, So the changes in the color purity in relation to (Nb) fluctuation can be applied in optical and industrial applications. Highlights • Reductions of dominant wavelength and reflectance when the bilayer numbers increase. • Changes in the color purity as function of bilayer period. • Machining tools coated with novel multilayer coatings. [ABSTRACT FROM AUTHOR]

TiCN/TiNbCN multilayer systems were synthetized on silicon substrates by radio frequency (r.f.) magnetron sputtering with alternatively changing the sputtering plasma composition between pure Ti+C and Nb elements under a reactive mixture of Ar/N2. Bilayer numbers were increased from nanometric range (15 nm) to higher micrometric range (1.5 μm). The structural and chemical properties were analyzed by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), cross-sectional transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), and optical properties via color purity. The multilayer period effect on the optical properties such as color purity was studied and the color dependence as function of bilayer number with niobium (Nb) modulation in the TiCN/TiNbCN system determined. The spectra for all layers showed high reflectance at large wavelengths, e.g., 92% for the TiNbCN layer, 89% for the TiCN layer, and about 75% for the TiCN/TiNbCN multilayer deposited with n = 200 and Λ = 15 nm. So the changes in the color purity present novel color applied on machining tools (tungsten carbide insert) in relation to (Nb) fluctuation which can be applied in optical and industrial applications. [ABSTRACT FROM AUTHOR]

A novel red SrLaGaO 4 : Eu3+ phosphor was successfully synthesized by solid-phase sintering method. X-ray diffractometer characterization shows that the phosphor possesses a tetragonal phase with a space group of I4/mmm. XPS spectroscopy characterized the chemical composition and the presence of trivalent europium in samples. Under 395 nm excitation, the emission spectra showed one strong peak at 618 nm subjected to electronic transition of 5D 0 →7F 2. The quantum yield of the SrLaGaO 4 : 0.3Eu3+ is 90.9%. At 423 K, the luminous intensity of SrLaGaO 4 : 0.3Eu3+ phosphor is 60.9% of the initial value. Besides, the chromaticity coordinates of SrLaGaO 4 : 0.3Eu3+ is (0.6467, 0.353) and the color purity is 99.56%. Finally, white LED with chromaticity coordinates of (0.36, 0.37) was prepared by mixing sample with commercial green/blue phosphors. In conclusion, SrLaGaO 4 : Eu3+ phosphor is a very promising light-emitting material for WLED devices. (a) Fluorescence quantum yield of SrLa 0.7 Eu 0.3 GaO 4 sample; (b) White-LED prepared with SrLa 0.7 Eu 0.3 GaO 4 and commercial blue/green phosphor. [Display omitted] • SrLaGaO 4 : Eu3+ phosphor was first reported with a quantum yield of 90.9% for the optimal sample. • The SrLaGaO 4 : 0.3Eu3+ has a high color purity of 99.56%. • Bright white-LED with coordinates (0.36, 0.37) were prepared by SrLaGaO 4 : 0.3Eu3+ phosphor. [ABSTRACT FROM AUTHOR]

Reddish-orange emitting CaLa 4 Ti 4 O 15 :Sm3+ phosphors were synthesized via a simple solid-state reaction. The synthesized CaLa 4 Ti 4 O 15 :Sm3+ phosphors revealed dominant excitation at 408 nm and emission at 601 nm with the 6H 5/2 → 4F 7/2 and 4G 5/2 → 6H 7/2 transitions, respectively. The transitions are governed by dipole-dipole interaction in the CaLa 4 Ti 4 O 15 :Sm3+ luminescent material. The morphology and crystal structure were investigated, and the material synthesis and chemical compositions were also confirmed. In a study of the effect of Sm3+ ion concentration on the luminescent properties of CaLa 4 Ti 4 O 15 :Sm3+ phosphors, the optimized concentration was found to be 5 mol%. The optimized phosphor powder exhibited Commission Internationale de l′Eclairage (CIE) chromaticity coordinate of (0.610, 0.390) under 408 nm illumination, and the thermal stability was also measured, exhibiting good thermal stability of about 81.7% at 423 K and 67.95% at 483 K. The white light-emitting diode (WLED) device was packaged using CaLa 4 Ti 4 O 15 :Sm3+ phosphors, together with commercial phosphors. The fabricated WLED device exhibited good correlated color temperature and color rendering index values of 5461 K and 83.97, respectively with (0.3341, 0.3997) CIE chromaticity coordinate. The CaLa 4 Ti 4 O 15 :Sm3+ materials as a reddish-orange emitting phosphor are expected to be a highly promising candidate for WLED applications. [Display omitted] • Novel CaLa 4 Ti 4 O 15 :Sm3+ orange-reddish-emitting phosphor materials were prepared. • The concentration quenching and thermal quenching mechanism of the phosphor were investigated. • The color purity of the optimized CaLa 4 Ti 4 O 15 :0.05Sm3+ phosphor was as high as 94.73%. • The CaLa 4 Ti 4 O 15 :0.05Sm3+ phosphor exhibited good thermal stability of 81.7% at 423 K. • The fabricated WLED revealed good CRI and CCT values of 83.97 and 5461 K. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two benzoxazole-based pure/deep blue emitters with bar-like structure are developed. • Rich C–H∙∙∙π interactions impart superior mobilities and optical properties of emitters. • Nondoped device achieves deep-blue emission with CIE y coordinate of 0.048 at 427 nm. • Deep-blue device demonstrates a best-in-class EQE of 8% for similar light colors. • Both blue OLEDs exhibit low efficiency-roll at a high luminance of 10000 cd m−2. Developing a high-performance nondoped deep-blue luminescent material that meets the substantial demand of high-definition organic light-emitting diodes (OLEDs) is significant and challenging. Herein, two highly efficient bar-like pure-blue and deep-blue materials, namely, PIPMePBO and PIPDMePBO, respectively, are designed and synthesized. Rigid planar phenanthroimidazole (PI) and benzoxazole (PBO) moieties are linked to construct a conjugated structure for a regulated aggregation pattern in both single crystals and evaporation films. This approach helps enhance and balance their carrier mobilities for excellent, stable OLED efficiency. Furthermore, different numbers of steric hindrance methyl groups are added to the π-conjugated bridge. This not only avoids potential conjugation quenching and aggregation redshift but also benefits the excited-state constructions for the regulation of blue purity. Results show that the double-methyl-substituted PIPDMePBO, with a moderate charge-transfer excited state, shows nondoped deep-blue electroluminescence with Commission Internationale de l'Eclairage coordinates of (0.156, 0.048). Its maximum luminescence is 12212 cd m−2. Remarkably, the nondoped OLED based on PIPDMePBO exhibits an excellent external quantum efficiency of 8.0%, with an efficiency roll-off of only approximately 12%, even at 10000 cd m−2. These findings are among the best for nondoped deep-blue fluorescent OLEDs with similar light colors. [ABSTRACT FROM AUTHOR]

Abstract Microwave-assisted synthesis of red-emitting ZnGa 2-x Eu x O 4 (x = 0.005, 0.008, 0.010, 0.012, 0.015) nanoparticles is reported. Salient features of this method are: 10 min are sufficient to obtain well-crystallized, phase-pure nanoparticles; synthesis upto 2 g/batch can be accomplished with high yields (>90%) at a low temperature of 200 °C; the obtained nanoparticles are near-spherical and of ∼7 nm size as seen by HR-TEM; as-prepared nanoparticles show intense red emission at 615 nm due to the 5D 0 → 7F 2 transition, when excited at 395 nm. The structural and optical properties of the ZnGa 2-x Eu x O 4 were studied by XRD, HR-TEM, FE-SEM, FT-IR and time-resolved photoluminescence (PL) spectroscopy. ZnGa 1.99 Eu 0.01 O 4 nanoparticles, which showed the most intense red emission, were studied for the effect of annealing (in air) on their optical properties. Annealing at up to 1000 °C (i) enhanced crystallinity and the crystallite size increased from ∼7 nm in the as-prepared material to ∼46 nm (ii) enhanced emission intensity, and moved the CIE coordinates towards red. Photoluminescence decay curves displayed two lifetimes, implying the distribution of Eu3+ (i) on particle surface (ii) within the host lattice; the distribution gradually changes with annealing. The peak fitting of the emission spectra implies C 2v site symmetry around Eu3+. A detailed Judd–Ofelt analysis has been presented. The samples annealed at 600–800 °C showed ∼58% quantum efficiency. The color purity could be increased to 87% by varying the Eu3+ content. Our report demonstrates the efficacy of swift microwave-assisted synthesis (10 min) in providing a red phosphor of high color purity suitable for LEDs and display applications. Highlights • Nanocrystalline (7 nm) ZnGa 2-x Eu x O 4 synthesized (2 g/batch) within 10 min at 200 °C. • Red emission enhanced with annealing; showed ∼58% quantum yield & 87% color purity. • Absence of green emission indicated probable host-to-dopant energy transfer. • PL decay showed two lifetimes due to presence of Eu3+ on surface & in host lattice. • Swift synthesis reported here is well-suited for other phosphors. [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]

• New blue phosphors, Pt complexes with tetradendate ligands. • The highest horizontal dipole orientation among doped Pt(II) complexes. • Depp blue OLEDs with CIE y values < 0.1 and external quantum efficiencies over 20% • New guidance for how to increase the Θ of Pt(II) complexes. The dedication of researchers has gradually allowed organic light-emitting diodes (OLEDs) to replace liquid crystals and/or inorganic light-emitting diodes (LEDs) in displays, signage, and lighting. However, the blue-emitting materials of OLEDs exhibit low efficiency and short lifetimes. Tetradentate Pt(II) complexes have the potential to serve as the next generation of blue emitters because of their narrow emission spectra, high photoluminescence quantum yields (PLQYs), and rigid molecular structures. The horizontal dipole ratio (Θ) is one of the most important factors that determines OLED efficiency. Unfortunately, however, high-level horizontal orientation data concerning Pt(II) complexes are available for only non-doped crystalline Pt(II) complexes, which exhibit excimer emission. Herein, we report a new strategy by which to control the orientation of Pt(II) complexes doped into host materials. The use of various aliphatic groups in different positions changes the molecular orientation. Therefore, a Θ of 79% is achieved; this is the highest value thus far for doped Pt(II) complexes. Additionally, we fabricated deep blue OLEDs with CIE y values < 0.1 and external quantum efficiencies over 20% using the developed Pt(II) complexes. The results offer new guidance for how to increase the Θ of Pt(II) complexes. [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]

Monoclinic NaSrB 5 O 9 :Sm 3+ phosphors were synthesized by a conventional solid-state reaction method in air. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed that the Sm 3+ ions preferably occupy Sr 2+ cation sites in the NaSrB 5 O 9 host lattice. The doping-dependent crystallite size and lattice strain on the X-ray peak broadening of the NaSrB 5 O 9 :Sm 3+ phosphor was determined by the Scherrer and Williamson–Hall (W–H) methods. Trigonally and tetrahedrally coordinated boron atoms in the phosphors were confirmed by confocal Raman analysis. Under near-UV excitation (402 nm), the NaSrB 5 O 9 :Sm 3+ phosphors emitted reddish-orange light at 604 nm that corresponds to the 4 G 5/2 → 6 H 7/2 transition. The concentration quenching mechanism between the two Sm 3+ ions within the host was proved to be the dipole-dipole interaction, and the critical distance was found to be 22.29 Å. The fitted luminescence decay curves in terms of a second-order exponential model suggest that the Sm 3+ ions possess two different kinds of environments in the host lattice, which was supported by XPS analysis. The defects acting as trapping centers were investigated by thermoluminescence glow curves. The γ-irradiated NaSrB 5 O 9 :Sm 3+ phosphors show two major dosimetric glow peaks centered at about 188.83 and 378.66 °C, indicating two different kinds of trapping centers in the phosphors. [ABSTRACT FROM AUTHOR]

Eu 2+ ion doped into a suitable host results in an efficient luminophore with engineering relevance; however stabilizing this ion in a host is known to be a challenge. Here we report a novel approach for the synthesis of efficient CaAl 2 O 4 phosphor containing Eu 2+ luminophore and Cr 3+ activator. CaAl 2 O 4 :Eu 2+ , Cr 3+ is prepared by a solution combustion (SCS) method using (i) urea, (ii) oxalyl dihydrazide (ODH) and (iii) fuel-blend (in which overall fuel to oxidizer ratio (F/O) = 1). A Multi-channel thermocouple setup is used to measure the flame temperatures to study the nature of combustion of various fuel mixtures. The variation of adiabatic flame temperature is calculated theoretically for different urea/ODH mixture ratios according to thermodynamic concept and correlated with the observed flame temperatures. Blue emission of the CaAl 2 O 4 :Eu 2+ phosphor is enhanced ∼20 times using the fuel-blend approach. Using the observed reaction kinetics, and the known chemistry of smoldering type combustion, a mechanism is proposed for the observed stabilization of Eu 2+ ion in the fuel-blend case. This also explains the observed improvement in blue light emission. We show that the right choice of the fuel ratio is essential for enhancing photoluminescence (PL) emission. The PL intensity is highest for ODH lean and urea rich combination (i.e. when the ratio of ODH:urea is 1:5); measured color purity is comparable to commercial blue phosphor, BAM:Eu 2+ . [ABSTRACT FROM AUTHOR]

A series of novel fused-ring spiro compounds, spiro[benzo[ij]tetraphene-7,9'-fluorene] (SBTF) derivatives containing an end-capping aryl substituent at both the C3 and C10-positions hasbeen designed and synthesized via multi-step Suzuki coupling reactions. 3-(1-Naphthyl)-10-phenylSBTF (1N-PSBTF), 3-(2-naphthyl)-10- phenylSBTF (2N-PSBTF) and 3-[4-(1-naphthyl)phenyl]-10-phenylSBTF (NP-PSBTF) showed improved glass transition temperatures (Tg) with good thermal stability. Their photophysical, electrochemical, and electroluminescent properties were investigated and were used to construct blue organic light emission diodes (OLEDs). The typical OLED devices showed excellent performance; the NP-PSBTF-based device exhibited highly efficient deep blue-light emission with a maximum efficiency of 5.27 cd/A (EQE, 4.63%) with CIE (x = 0.133, y = 0.144). According to these characteristics, these deep-blue light emitting materials have sufficient potential for fluorescent OLED applications. [ABSTRACT FROM AUTHOR]