White Color Emission Research Articles

Rare earth Nd3+-doped organic-inorganic hybrid perovskite quantum dots for white LED

Lead halide perovskite quantum dots (QDs) have garnered significant attention due to their tunable band gaps, unique quantum confinement effects, and high photoluminescence quantum yields (PLQYs). Among them, Organic-inorganic QDs make them promising candidates for optoelectronic devices such as quantum dot light-emitting diodes (QLEDs), solar cells, lasers, and photodetectors. However, the toxicity of lead (Pb) has raised environmental and health concerns, hindering their industrial application. To alleviate concerns about heavy metals Pb, extensive research has been conducted on B-site doping and the development of lead-free perovskites. Herein, we firstly developed B-site doping strategy on organic-inorganic hybrid perovskite QDs via rare-earth elements. Neodymium (III) (Nd3+) doped FAPbBr3 QDs were prepared through the ligand-assisted reprecipitation method at room temperature. The B-site doping strategy could alleviate the heavy metal problem of Pb and modulate the band gap of FAPbBr3 QDs facilely. The results demonstrated that increasing the concentration of Nd³⁺ can change the emission of FAPbBr₃ QDs from pure green to deep blue. Specifically, we achieved highly pure blue emission (∼438 nm) with a full width at half maximum (FWHM) of 13 nm for Nd³⁺-doped FAPbBr₃ QDs. Time-resolved photoluminescence (TRPL) spectroscopy revealed a decrease in the lifetime of FAPbBr₃ QDs from 22.86 to 15.46 ns as the doping concentration increased. Additionally, we fabricated a white LED (WLED) utilizing blue-emitting Nd³⁺-doped FAPbBr₃, green-emitting FAPbBr₃ QDs, and red QDs, achieving a white emission color coordinate of (0.33, 0.36). This study pioneers the application of B-site rare-earth doping in organic-inorganic hybrid perovskite QDs, demonstrating that B-site composition engineering is a reliable strategy to further exploit the perovskite family for wider optoelectronic applications.

Development of white organic light emitting diodes based on carbazole-derived compounds

The object of research is the thermal, photophysical, and electrophysical properties of newly synthesized carbazole-derived compounds and organic light-emitting structures based on them. The problem consists in the comprehensive solution of scientific and technical problems of improving the characteristics of white organic light-emitting diodes (OLED), expanding their emission spectrum, improving color and energy characteristics. The results of the thermal, electrophysical and photophysical properties of the investigated carbazole compounds were obtained. They demonstrated good thermal stability. Absorption spectra in solid films were recorded in the range of 300–350 nm. Photoluminescence spectra were observed at a wavelength of 407 nm for the first and second compounds and 430 nm for the third. The quantum yield of photoluminescence in films for compounds 1, 2, and 3 was 16 %, 7 %, and 7 %, respectively. Organic light-emitting structures of white emission color with color coordinates (0.31, 0.35), (0.32, 0.34) and (0.38, 0.34) close to natural white light (0.33, 0.33) were formed using the thermovacuum sputtering method. The turn-on voltage of the white OLED is 6 V, the maximum brightness of the light-emitting structures was 10,000 cd/m2. The devices demonstrated a sufficiently high external quantum efficiency of 5 % to 7 %. The obtained results are explained by the mixing of different types of electroluminescence, namely excitonic and electromeric. Electromeric radiation is obtained due to transport layers. This approach improves such an important parameter of white light as its quality, which includes color coordinates and color rendering index. Due to their color characteristics, white light-emitting diodes based on carbazole-derived compounds are promising candidates for use in modern lighting systems. A separate advantage of these light-emitting structures is the dependence of the color gamut of their radiation on the applied voltage. In addition, organic LEDs based on carbazole-derived compounds have low energy consumption and are environmentally friendly due to the absence of toxic substances in their design, which creates prerequisites for both global energy savings and a reduction of the industrial burden on the environment.

Controllable Dopamine Conjugation Boosts Fluorescence, Biocompatibility, and PET Imaging‐Guided Toxicity Assessment of Polycations

AbstractAs well known in bioactives delivery and cancer/inflammation theranostics, polycations have recently extended their biomedical potentials in reducing visceral fat, embolizing body fluid, modulating blood coagulation, and ameliorating hyperammonemia. However, positive charges that dominate various action mechanisms, often raise risks in biosafety concerns. Also, the lack of intrinsic imaging properties of polycations makes it challenging to uncover their pharmacokinetic profiles in living objects. Herein, dopamine conjugation is demonstrated controllable and highly efficient in boosting the fluorescence or even white color emission of various polycations including hyperbranched poly(amido amine) (HPAA), polyethyleneimine and poly‐L‐lysine. By shielding partial surface positive charges, increasing hydrophobicity, and inducing aqueous self‐assembly, dopamine conjugation can significantly enhance the biocompatibility and decrease the toxicity and immunogenicity of polycations. Furthermore, the catechol‐metal binding interaction facilitates the accessibility of polycation‐based positron emission tomography (PET) probes. Different tissue uptake and biodistributions of gallium‐68‐radiolabeled HPAA before and after dopamine conjugation indicate that PET imaging can be a useful supplement to evaluate the dynamic toxicities of polycations.

Luminescence properties of Bi3+/Sm3+ co-doped K3Gd5(PO4)6 phosphors for self-referencing optical thermometry.

Potassium gadolinium phosphates [K3Gd5(PO4)6] co-doped with Bi3+/Sm3+ phosphors were prepared by traditional solid-state method. Their structure, morphology, luminescence properties, energy transfer, temperature sensing performance and thermal stability have been systematically investigated. The emission and excitation spectra, as well as decay curves were recorded to study the luminescence mechanism. By co-doping Bi3+/Sm3+, white emission color can be obtained. In addition, the emission intensity ratios of Bi3+ and Sm3+ ions present excellent temperature sensing performance in a wide temperature range. The maximum relative sensitivities of K3Gd5(PO4)6 doped with Bi3+/Sm3+ can reach to 3.13% K-1. In addition, K3Gd5(PO4)6:Bi3+,Sm3+ phosphors exhibit high thermal stability of about 55.3% at 423 K compared to room temperature.

High solid-state photoluminescence quantum yield of carbon-dot-derived molecular fluorophores for light-emitting devices.

Several recent studies of carbon dots (CDs) synthesized by bottom-up methods under mild conditions have reported the presence of organic molecular fluorophores in CD dispersions. These fluorophores have a tendency to aggregate, and their properties strongly depend on whether they are present in the form of discrete molecules or aggregates. The aggregation becomes more prominent in the solid state, which motivates the study of the properties of the fluorophores associated with CDs in the solid state. Here, we report the solid-state characterization of N4,N11-dimethyldibenzo[a,h]phenazine-4,11-diamine (BPD) - a molecular fluorophore that forms CDs. Discrete BPD molecules show excitation-wavelength-independent photoluminescence (PL) emission in the green wavelength region at ∼520 nm. However, additional blue PL is also observed due to aggregation, making the PL emission significantly broad. For detailed studies, BPD is mixed in different solid matrices, and it is observed that the PL quantum yield (PLQY) of BPD films strongly depends on the concentration of BPD in the solid matrices. Increasing the concentration of BPD results in a considerable decrease in the PLQY. The PLQY of the films with an optimum concentration of BPD is 75.9% and 40.2% in polymethyl methacrylate and polystyrene, respectively. At higher concentrations, these PLQY values decrease to ∼11%. The significant decrease in the PLQY is ascribed to reabsorption and nonradiative exciton decay that is facilitated by BPD aggregation at higher concentrations. Finally, light-emitting devices (LEDs) were fabricated with almost pure white emission color, having CIE (International Commission on Illumination) coordinates of (0.35, 0.37) using BPD in the color-converting layer of blue-pumped LEDs. The device shows a luminous efficiency 3.8 lm W-1 and luminance of 43 331 cd m-2.

A Comparative Study between Blended Polymers and Copolymers as Emitting Layers for Single-Layer White Organic Light-Emitting Diodes.

Extensive research has been dedicated to the solution-processable white organic light-emitting diodes (WOLEDs), which can potentially influence future solid-state lighting and full-color flat-panel displays. The proposed strategy based on WOLEDs involves blending two or more emitting polymers or copolymerizing two or more emitting chromophores with different doping concentrations to produce white light emission from a single layer. Toward this direction, the development of blends was conducted using commercial blue poly(9,9-di-n-octylfluorenyl2,7-diyl) (PFO), green poly(9,9-dioctylfluorenealt-benzothiadiazole) (F8BT), and red spiro-copolymer (SPR) light-emitting materials, whereas the synthesized copolymers were based on different chromophores, namely distyryllanthracene, distyrylcarbazole, and distyrylbenzothiadiazole, as yellow, blue, and orange-red emitters, respectively. A comparative study between the two approaches was carried out to examine the main challenge for these doping systems, which is ensuring the proper balance of emissions from all the units to span the entire visible range. The emission characteristics of fabricated WOLEDs will be explored in terms of controlling the emission from each emitter, which depends on two possible mechanisms: energy transfer and carrier trapping. The aim of this work is to achieve pure white emission through the color mixing from different emitters based on different doping concentrations, as well as color stability during the device operation. According to these aspects, the WOLED devices based on the copolymers of two chromophores exhibit the most encouraging results regarding white color emission coordinates (0.28, 0.31) with a CRI value of 82.

Exploring luminescent color tunability and efficient energy transfer mechanism of a single-phased hexagonal nanophosphor for white light emitting diodes (WLEDs) application

Nowadays, NUV-triggered phosphor-converted white light-emitting diodes (pc-WLEDs) have gained prominence as substantial alternatives to conventional incandescent and fluorescent lamps as a source of illumination. In this study, we have successfully developed a Tm3+ codoped La2O3:Sm3+ nanophosphor and investigated its potential suitability for application in white light-emitting diodes (WLEDs). X-ray diffraction (XRD) analysis was conducted to examine the phase impurity and structural characteristics of the synthesized nanophosphor. The analysis confirmed the formation of a single-phase La2O3 nanophosphor with a hexagonal crystal structure. The FT-IR spectrum of the synthesized nanophosphor exhibited distinct peaks associated with the vibrational frequencies of La-O bonds. The peaks observed in the fingerprint region of the spectrum, indicate the presence of La-O atoms in the nanophosphor. However, the HR-TEM analysis confirmed that the prepared nanophosphor had a polycrystalline nature and the observed particle sizes lay within the nanoscale range. The incorporation of Tm3+ ions into the host matrix led to a reduction in the optical band gap, leading to enhanced emission intensity. The photoluminescence (PL) study reveals that the Tm3+ ion exhibited blue emission upon excitation at 360 nm, whereas the Sm3+ ion emits reddish-orange light when excited at 379 nm and 408 nm, respectively. However, under 325 nm excitation, the nanophosphor exhibited a white emission color that resulted from the blending of colors emitted by both Tm3+ and Sm3+ ions. This unique finding suggests that this nanophosphor has the potential to generate white light specifically under this particular excitation wavelength. The efficient energy transfer between Tm3+ and Sm3+ ions was attributed to the electric multipolar interaction between the nearest neighbor ions, leading to a quenching phenomenon. Furthermore, the photometric analysis revealed that the correlated color temperatures (CCTs) associated with the emitted white light were found to be higher than 4000 K. Thus, based on these characteristics, it can be inferred that the prepared nanophosphor has the potential to be utilized as a cool white-emitting nanophosphor for single-phased WLEDs application.

Highly efficient color mixing system for the fine-tuning of white light–PLEDs using blue and red poly-chromophores

The fine tuning of color and white light emission was achieved from the simple blending of two different types of polychromophores. The π-conjugated polymeric chromophores (blue and red) were synthesized and characterized for white light polymer emitting diode (WPLED) applications. The binary luminescent materials, Blue polymeric chromophore (BPy) and (Red polymeric chromophore (RPy), were obtained from the respective monomers via a standard Suzuki coupling reaction. The tuning of colors and white light emission were attained directly mixing of two polymeric chromophores (blue, red) in different ratio. The prepared polymer materials were confirmed using standard tehniques such as, Fourier transform infrared (FT-IR) and 13C and 1H-nuclear magnetic resonance (NMR) spectroscopy, while the gel-permeation chromatography result revealed the polymeric properties of the materials. The polymeric materials surfaces morphologies were analysed throught the FE-SEM and AFM analysis. The TGA (Thermogravymetric analysis) used to study the thermal property of the two prepared polymeric materials. The UV–visible and fluorescence spectrophotometry was applied to examine the optical features of the materials. The BPy and RPy polymers shows absorption peaks at 375 nm and 426 nm, respectively. The obatined emission peaks of BPy and RPy are at 426 nm and 603 nm, respectively. These results show that BPy and RPy belong to the blue and red emissive categories, and the white light emission was obtained with the mixing ratio of BPy(80%)-RPy(20%). The bandgap of these materials was calculated by cyclic voltammetry, and the theoretical bandgap of the materials was calculated by density functional theory analysis. Finely structured devices were fabricated, and the efficiencies of the BPy, RPy, and BPy-RPy were analyzed to assess the luminance productivity of the materials. In summary, this paper proposes a simple method to achieve white color emission by mixing polymeric chromophores at different ratios.

White-light luminescence from Tm3+-doped borosilicate glass-ceramics synthesized by the sol-gel route

White-light luminescent Tm3+-doped borosilicate glass-ceramics were synthesized by the sol-gel method. The materials are predominantly amorphous with some embedded nanocrystals of H3BO3 and B2O3 with sizes ranging from 4 to 10 nm, which decrease as the Tm2O3 content is increased. Moreover, the glass transition and crystallization temperatures enhance with the Tm2O3, showing higher thermal stability in the glass-ceramic with 0.50 mol%. Also, the addition of Tm2O3 promotes an increase in the non-bridging oxygen concentration, the occurrence of the boric anomaly, and the incorporation of a higher amount of C species (CC and CO bonds) into the reticular structure of the glass ceramic. Therefore, the optical bandgap reduces (3.62–3.47 eV) while the photoluminescence intensity increases, being maximum at 0.75 mol% of Tm2O3. Interestingly, the luminescent glass-ceramics show a white-emission color, CIE coordinates are (0.31–0.33, 0.33–0.34) instead of those corresponding to blue, which is what usually occurs in other Tm3+-doped materials. This characteristic photoluminescence emission is due to the 1D2→3F4 electronic transitions of Tm3+ ions and the π– π* and n–π* transitions of CC and CO bonds originated by the carbon remnants inside the glass-ceramics. The released white emission has a correlated color temperature of 5600–6650 K, a color rendering index of ∼88, and a quantum yield of 12.3%. These materials are promising candidates for their use as phosphors in solid-state white-light-emitting devices.

Dependence of the Color Tunability on the H2Pc Thickness in DC-Voltage-Driven Organic Light-Emitting Diodes

Dependence of the color tunability on the metal free Phthalocyanine (H2Pc) layer thickness in DC-voltage-driven organic light-emitting diodes (OLEDs) was investigated. A H2Pc layer was employed as a blue/red emission layer, which was prepared on an Alq3 green emission layer. The thickness of the H2Pc layer varied from 5 to 30 nm, with a step of 5 nm. The fabricated color-tunable OLEDs (CTOLEDs) were subjected to a thermal treatment layer for 2 min at a temperature of 120 °C to improve the interface properties, especially between H2Pc and Alq3. The current density–voltage–luminance characteristics and Commission Internationale de L’Eclairage (CIE) coordinates of the CTOLEDs with and without thermal treatment were measured, and their energy band diagrams were analyzed with respect to the H2Pc thin film thicknesses. In addition, the recombination rates at the interfaces between the hole transport layer and Alq3 and the H2Pc/electron transport layer of the CTOLEDs with and without thermal treatment were theoretically investigated using a technology–computer-aided design (TCAD) program. The experimental and theoretical results showed that the emission color temperature from cool white to warm white at a low voltage can be controlled by adjusting the thickness of the H2Pc layer in the CTOLED. It was verified that the thermally treated H2Pc thin film layer acted as a barrier that prevented electrons from being transferred to the Alq3 at low applied voltages, resulting in white color emission with temperature tunability. The CTOLED with a 20 nm of H2Pc layer demonstrated the best stable interface state and stability, resulting in the lowest driving voltage, relatively high luminance, and optimal light emission uniformity, respectively.

Lead-Free Inorganic Nanoparticles of Perovskite Embedded within Waterproof Nanofiber Films for White Color Emission

Organic polymers can enhance the environmental stability of inorganic perovskite nanocrystals (IPNCs) by encapsulation. We fabricated lead-free IPNCs embedded in waterproof and luminous polymer fibers. The encapsulated perovskite nanocrystals within polystyrene (PS) polymers, CsCu2I3@PS (Y-fiber), and Cs3Cu2I5@PS (B-fiber) were prepared by one-step electrospinning of the solutions containing the precursors (CsI and CuI) and PS. The embedded nanocrystals had highly uniform sizes, spatial distribution, and well-developed crystal structures. The Y- and B-fibers showed yellow and blue emission under ultraviolet (UV) light, respectively, and a white emission fiber layer was fabricated via dual-nozzle coelectrospinning using CsCu2I3 and Cs3Cu2I5 precursor solutions. The as-prepared B-fibers exhibited improved water stability without changing the crystal structure and photoluminescence (PL) emission in deionized water for 20 days. To enhance environmental stability and mechanical properties, transparent poly(dimethylsiloxane) (PDMS) films containing IPNCs@PS fibers presented strong PL emission without peak shift under 100% tensile strain, indicating highly flexible and humidity-durable characteristics.

Synthesis, adjustable-color emission and energy transfer of Ba2MgSi2O7:Sm3+, Bi3+ phosphors

Ba2MgSi2O7:M (M = Bi3+, Sm3+, Sm3+/Bi3+) phosphors are synthesized in air by the high-temperature solid-state reaction method. All samples are confirmed to be a pure phase. With a 316 nm excitation wavelength, Ba2MgSi2O7:Bi3+ shows blue-white emission including a broad emission band in the range of 340 - 750 nm, and Ba2MgSi2O7:Sm3+, Bi3+ emits a adjustable-color light with the change of the ratio of Sm3+ to Bi3+ ions. Under excited at 402 nm, Ba2MgSi2O7:Sm3+ and Ba2MgSi2O7:Sm3+, Bi3+ emit orange-red light with emission spectrum region from 545 nm to 750 nm, which contain four emission bands peaking at ∼560, 598, 646 and 704 nm due to the 4G5/2 → 6H5/2, 6H7/2, 6H9/2, and 6H11/2 transitions of Sm3+ ion, respectively. Ba2MgSi2O7:Sm3+, Bi3+ under excitation at 316 nm can show a white-color emission by changing the ratio between Sm3+ and Bi3+ ions. Lifetimes of samples decrease with increasing doped ion (Sm3+ or Bi3+) concentration. We explain the luminous mechanism of samples by the schematic energy level diagrams of Bi3+ and Sm3+ ions in Ba2MgSi2O7:Sm3+, Bi3+.

Red color Sr2NaMg2V3O12:Eu3+ phosphor with high thermal stability for w-LEDs

Sr2NaMg2V3O12:xEu phosphors with uniform particle size/morphology and good dispersion can be synthesized via solid state reaction. Under the optimum excitation wavelength of ∼340 nm, the Sr2NaMg2V3O12:xEu phosphor displays the broad emission band at ∼500 nm (blue-green emission, 3T1,2 → 1A1 transition of [VO4]3– and sharp emission peak at ∼610 nm (red emission, 5D0→7F2 transition of Eu3+), respectively. With the Eu3+ content increasing, the emission intensity of [VO4]3– decreases gradually while the emission intensity of Eu3+ increases, which is ascribed to the energy transfer from [VO4]3– to Eu3+ ions. The decay time of [VO4]3– (∼500 nm) increases gradually with the Eu3+ content increasing. The energy transfer efficiency and mechanism of [VO4]3–→Eu3+ ions were analyzed, respectively. The emission color of Sr2NaMg2V3O12:xEu phosphor was regulated from green to red via altering the Eu3+ ions concentration. It is delightful for us that the white color emission can be just achieved when the Eu3+ content is 5 at% (x = 0.05), and the w-LED can be assembled. By studying the luminescence temperature dependence and activation energy of Sr2NaMg2V3O12:xEu phosphor, it is shown that the phosphor has good thermal stability. The Sr2NaMg2V3O12:xEu powder is expected to be a new type of phosphor widely used in light and display areas.

Low-temperature sintered Pr3+/Er3+ codoped Bi2Mo2O9 microcrystals for multimode optical thermometry and anti-counterfeiting

Lanthanide-doped oxide materials generally require high sintering temperatures for optical applications such as temperature sensing and anti-counterfeiting. In this work, the highly crystalline 1%Pr3+/1%Er3+ co-doped Bi2Mo2O9 phosphor is reported with a low sintering temperature of 923 K. Pr3+ in the Bi2Mo2O9 host has a narrow emission band of 3P0–3H6 transition at 624 nm due to the suppressed broadening of electronic transitions in the homogeneous crystal field. Multimode temperature sensing is realized based on the upconversion and downshifting emissions as well as the luminescence lifetimes of the as-prepared phosphor. The temperature sensing based on the downshifting emission bands of this phosphor at 530 and 624 nm achieves the maximum absolute and relative sensitivities of 0.693 K−1 at 568 K and 1.88% K−1 at 483 K, respectively. For anti-counterfeiting applications, this phosphor can display bright yellow fluorescence at the liquid nitrogen cooling temperature, rather than white or pale colors. The white-color emission of this phosphor excited by 254 nm can also be used for lighting. The lanthanide-doped Bi2Mo2O9 can achieve favorable luminescence performance at much lower sintering temperature than most oxide phosphors, and is not only stable but also has the potential for in-situ sintering on materials that are not resistant to high temperature.

White-light emission in Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4 nanoparticles

Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4 nanoparticles were synthesized using a microwave hydrothermal method and studied for white-light emission under 980 nm laser diode excitation. White upconversion (UC) light was successfully obtained with the appropriate control of blue, green, and red emissions by successfully tuning the Er3+ and Ho3+ concentrations in Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4, respectively. In addition, the white color emission was shown by the CIE chromaticity coordinates of samples. The energy transfer mechanisms are explained in detail based on the emission spectra and pump power density-dependent UC luminescence intensity in rare earth (Yb3+/Er3+/Tm3+ and Yb3+/Er3+/Tm3+/Ho3+)-doped α-NiMoO4 nanoparticles. The results indicate that Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-doped α-NiMoO4 nanoparticles can be good candidates for white-light devices.

White emitting 5ZnO-(5–2.5x)Ga2O3- 2.5xAl2O3–90SiO2 glass ceramic embedded with Mn doped Zn(Ga,Al)2O4 nanocrystals

Dual-emitting manganese ions singly doped 5ZnO-(5–2.5x)Ga 2 O 3 -2.5 xAl 2 O 3 –90SiO 2 glass-ceramic (GCs) samples, containing the alloyed Zn(Ga, Al) 2 O 4 nanocrystals with a size of about 5 nm, were successfully prepared by a sol-gel method under different heat treatment temperatures, demonstrating an excellent white light emission. We found that the formation of the ZnGa 2 O 4 nanocrystals began at 650 °C (absence of Al 2 O 3 , x = 0) while that of the ZnAl 2 O 4 crystals required a higher temperature of about 900 °C (presence of Al 2 O 3 , x = 2) in SiO 2 glasses. A nanostructured Zn(Ga, Al) 2 O 4 :Mn 2+ , Mn 4+ in the glass-ceramic was synthesized by Al 3+ replacing part of Ga 3+ . The doping of Al 3+ has effectively contributed to the existence of Mn 2+ , thus realizing the regulation of the valence state of manganese ions. The glass ceramic samples showed red emission arrived from the 2E g → 4A 2g transitions of Mn 4+ , green emission originated from the 4T 1 →6A 1 transition of Mn 2+ , and blue emission derived from the self-activation center of ZnGa 2 O 4 nanocrystalline. In particular, the 0.1%Mn doped the 5ZnO-(5–2.5x)Ga 2 O 3 -2.5xAl 2 O 3 –90SiO 2 glass-ceramic samples can provide white color emission depending on the Al doping concentration (x), x = 0.4–0.9 and the annealing temperature, 650–900 °C.

Chromaticity tunable realizable solution process single layer white organic light‐emitting diode

AbstractThe achievement of white color emission required simultaneous emission of optimized composition of blue, green, and red colors or at least two supplementary colors with similar distribution of emission intensities covering the entire visible spectrum ranging from 400 to 700 nm in solution‐processable white organic light‐emitting diodes (W‐OLEDs). In view of this information, different concentrations of polyvinylcarbazole (PVK), red polymer Nile Red, and blue polymers such as poly(9,9‐dioctylfluorenyl‐2,7‐diyl) (PF) and spirobifluorene derivative SPB‐02T were utilized to obtain white light emission in single‐layer W‐OLEDs. Coupled emissions of these materials with blue luminescence from PF and SPB‐02T and reddish emission from Nile Red presented white color due to energy transfer between the two polymers. Efficient solution‐processed W‐OLED devices were fabricated using a single layer light‐emitting film with optimized concentration of ternary blends. W‐OLED device performances were analyzed for their charge transport behavior depending on concentration of ternary blend. When it has been looked from the viewpoint of the closest to white color coordinates (0.33, 0.33), the W‐OLED device named mpn4 with PVK:SPB‐02T:Nile Red was the closest (0.33, 0.27). In consideration of energy transaction, voltage dependency in electroluminescence spectra proved that the existence of energy transfer in the mpn4‐based W‐OLEDs.

Copolyfluorenes containing carbazole or triphenylamine and Diethoxylphosphoryl groups in the side chains as white-light-emitting polymers

New copolyfluorenes containing 4,7-di-2-thienyl-2,1,3-benzothiadiazole and 2,1,3-benzothiadiazole or derivatives of naphthalimide as luminophores were synthesized under microwave heating. Charge-transporting carbazole, triphenylamine, or diphenyloxadiazole groups were introduced into the side chains of polymers through 9,9-bis-(4-phenoxy)-2,7-fluorene units. Copolyfluorenes were also modified via insertion of 10 mol% of 2,7-[9,9-bis-(6′-diethoxyphosphorylhexyl)]fluorene or dibenzothiophene-S,S-dioxide comonomer units into the polymer backbone. This study demonstrates the influence of chemical compositions, molecular masses of the polymers under investigation, and thermal treatment on microstructures of their films. Photo- and electroluminescent characteristics of the synthesized copolyfluorenes were determined. The best samples of devices manifested the luminance of 5110 cd m⁻2, the current efficiency of 1.33 cd A⁻1, and the CIE 1931 xy chromaticity coordinates of (0.339 0.364), or 7930 cd m⁻2, 2.18 cd A⁻1, and of (0.300 0.369) respectively. The effect of active layer thickness on the white emission color of polymer light-emitting diodes was revealed.

Photoluminescent properties of Sm3+ and Tb3+ codoped CaWO4 nanoparticles obtained by a one-step sonochemical method

Luminescent materials with LED applications can have your emission color controlled by rare earth doping. In this work, Sm3+- and Tb3+-codoped CaWO4 nanoparticles were obtained by a one-step sonochemical method. The nanoparticles were characterized by X-ray diffractogram (XRD), Raman scattering (RS) spectroscopy, The Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and visible ultraviolet spectroscopy (UV–Vis). The photoluminescent measurements were taken at room and lower temperatures for analysis of doping in emission color. The diffractograms indicate the single-phase CaWO4 with the scheelite structure and it was observed a reduction in the crystallite size as the doping. SEM and TEM images indicate the formation of nanospheres for pure and samarium-doped samples, while terbium doping results in the formation of nanorods. Room temperature photoluminescence spectra indicate a blue emission for the bare and samarium-doped CaWO4, while terbium doping emits at the green color. The codoping mixes the colors blue, green, and orange, indicating a potential material with white color emission.

Multicolor-emitting luminescent Y2O3:RE3+@SiO2-[RE3+(β-diketone)3] core@shell hybrids featuring dual RE3+ activator centers

Luminescent inorganic-organic hybrids find several applications such as in multifunctional devices or in bioimaging. In this regard, through a step-by-step process, inorganic-organic [email protected] hybrids based on spherically-shaped Y2O3:Eu3+@SiO2-[Tb(acac)3(Salen)] or Y2O3:Tb3+@SiO2-[Eu(dbm)3(Salen)] particles with diameter of 170 nm were fabricated from Y2O3:RE3+ (RE3+ = Eu3+ or Tb3+) coated with a layer of SiO2 (2.7 nm), that was amino-functionalized, followed by imino-functionalization to get Salen ligands to which were finally bonded to [RE(β-diketonate)3] complexes (β-diketonate = acetylacetonate, acac, or dibenzoylmethanate, dbm). The [email protected] architecture of the hybrids was confirmed by X-ray diffraction, FTIR and TEM. By changing the excitation pathways, the overall emitted color of both hybrids is tuned from green (Tb3+ emission) to red spectral region (Eu3+ emission), crossing the white color emission region due to the combination of the Eu3+, Tb3+ and Salen emissions. As an additional and interesting find, no energy transfer from the RE3+ in the core to the other RE3+ on the particle surface takes place, avoiding the quenching of both RE3+ luminescence. Therefore, the high 5D0 state quantum efficiency of Eu3+ (68%) and the multicolor emission qualify the hybrids for future photonic applications in multifunctional devices or in bioimaging.