Maximum Photoluminescence Emission Research Articles

La:ZnO nanoparticles: an investigation on structural, optical, and microwave properties

This paper presents the utilization of ethylene glycol monomethyl ether (EGME) during the synthesis of ZnO and La:ZnO with two tasks as a solvent and a fuel source within the gel combustion technique. The use of EGME for this purpose provides one-step production of the nanoparticles (NPs) and saves a considerable amount of time. The detailed characterization of the nanoparticles was carried out by X-ray diffractometer (XRD), scanning electron microscope (SEM), particle size analyzer, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Vector Network Analyzer (VNA) measurements, respectively. The NPs exhibited a hexagonal wurtzite structure with good crystallinity and a porous spongy morphology. The photoluminescence emission maxima of the synthesized NPs appeared at 500, 560, and 676 nm, upon excitation by the 372 nm of excitation. La:ZnO NPs showed significantly better photoluminescent characteristics than La-free ZnO forms. When excited at the same wavelength, La-free ZnO, 3%, and 7% La:ZnO exhibited 92, 45, and 35 μs average decay times, respectively. Finally, the microwave properties of the relative complex permittivity and permeability characteristics were also investigated and discussed in detail, which were derived from the scattering parameters of S11 and S21 in the X band regime.

A New Ultrafine Luminescent La2O3:Eu3+ Aerogel.

This paper reports on the synthesis and characterization of La2O3:Eu3+ luminescent aerogels fabricated by the sol-gel method and the supercritical drying technique. The % mol concentration of the Eu3+ ion was varied to study the effects on the luminescent properties of the aerogels. XRD and TEM analysis showed that the La2O3:Eu3+ aerogels exhibited a semi-crystalline behavior regardless of whether the concentration of europium was increased. SEM micrographs revealed a porous structure in the aerogels, which were composed of quasi-spherical nanoparticles that were interconnected and formed coral-shaped agglomerates. Photoluminescence spectroscopy characterization showed that the aerogels had an infrared emission located at λ = 793 nm, and the maximum photoluminescence emission intensity was observed for the aerogel with 50% Eu3+. The results demonstrate that, without heat treatment, it is possible to manufacture luminescent aerogels of rare-earth oxides that can be used in opto-electronic devices.

Exploring the luminescence of tin‐incorporated nickel‐sensitized lithium gallate short‐wave‐infrared phosphors

AbstractA series of Ni2+‐sensitized LiGa5O8 nanocrystals doped with varying amounts of Sn4+ were synthesized via a high‐temperature solid‐state method. X‐ray diffraction and scanning electron microscopy were employed to investigate the microstructure of the LiGa5O8 host, and optical spectroscopy was used to examine the effects of Sn4+ addition on the emission spectra and persistent luminescence (PersL) properties, which indicated a homogeneous distribution of the constituent elements in the phosphor. The Sn4+ incorporation led to an approximately sixfold enhancement of photoluminescence intensity at room temperature and decrease in the energy transition of Ni2+(3T2(3F)→3A2(3F)), which resulted in ∼65 nm bathochromic shift in the photoluminescence emission maxima. However, the addition of Sn4+ dopant led to a decrease in the quantum yield of luminescence compared to that of the original phosphor. Temperature‐dependent thermoluminescence measurements revealed that doping of LiGa5O8 with Sn4+ interfered with the Ni2+ trap centers. Moreover, Ni2+‐sensitized Sn4+‐doped LiGa5O8 nanocrystals exhibited an afterglow effect that persisted for up to 300 s.

Rapid Data-Efficient Optimization of Perovskite Nanocrystal Syntheses through Machine Learning Algorithm Fusion.

With the demand for renewable energy and efficient devices rapidly increasing, a need arises to find and optimize novel (nano)materials. With sheer limitless possibilities for material combinations and synthetic procedures, obtaining novel, highly functional materials has been a tedious trial and error process. Recently, machine learning has emerged as a powerful tool to help optimize syntheses; however, most approaches require a substantial amount of input data, limiting their pertinence. Here, three well-known machine-learning models are merged with Bayesian optimization into one to optimize the synthesis of CsPbBr3 nanoplatelets with limited data demand. The algorithm can accurately predict the photoluminescence emission maxima of nanoplatelet dispersions using only the three precursor ratios as input parameters. This allows us to fabricate previously unobtainable seven and eight monolayer-thick nanoplatelets. Moreover, the algorithm dramatically improves the homogeneity of 2-6-monolayer-thick nanoplatelet dispersions, as evidenced by narrower and more symmetric photoluminescence spectra. Decisively, only 200 total syntheses are required to achieve this vast improvement, highlighting how rapidly material properties can be optimized. The algorithm is highly versatile and can incorporate additional synthetic parameters. Accordingly, it is readily applicable to other less-explored nanocrystal syntheses and can help rapidly identify and improve exciting compositions' quality.

One-Pot Synthesis and Characterization of CuCrS2/ZnS Core/Shell Quantum Dots as New Blue-Emitting Sources.

In this paper, we introduce a new blue-emitting material, CuCrS2/ZnS QDs (CCS QDs). To obtain bright and stable photoluminescent probes, we prepared a core/shell structure; the synthesis was conducted in a one-pot system, using 1-dodecanethiol as a sulfur source and co-ligand. The CCS QDs exhibited a semi-spherical colloidal nanocrystalline shape with an average diameter of 9.0 nm and ZnS shell thickness of 1.6 nm. A maximum photoluminescence emission peak (PL max) was observed at 465 nm with an excitation wavelength of 400 nm and PLQY was 5% at an initial [Cr3+]/[Cu+] molar ratio of one in the core synthesis. With an off-stoichiometric modification for band gap engineering, the CCS QDs exhibited slightly blue-shifted PL emission spectra and PLQY was 10% with an increase in initial molar ratio of 2.0 (462 nm PL max). However, when the initial molar ratio exceeded two, the CCS QDs exhibited a lower photoluminescence quantum yield of 4.5% with 461 nm of PL max at the initial molar ratio of four due to the formation of non-emissive Cr2S3 nanoflakes.

Structural and Luminescence Analysis of Low Temperature Solution Combustion Derived White Light Emitting Y2(1-x)Dy2xZr2O7 Nanophosphors for WLEDs

White light emitting dysprosium doped rare-earth zirconate Y2(1-x)Dy2xZr2O7 (x = 0.5 to 5 mol%) crystalline phosphors in nano-regime were obtained using urea supported solution combustion methodology at low temperature 650 ºC. Presence of fluorite structure having cubic symmetry with Fm3m space group was analyzed by powder X-ray diffraction patterns. Spherical shaped nanoparticles with clear boundaries were observed by surface morphological studies. Diverse elements Y, Zr, Dy and O were present in the optimized nanophosphors as examined by energy dispersive X-ray analysis. Upon near ultraviolet (NUV) excitation at 354 nm wavelength, the Y2(1-x)Dy2xZr2O7 phosphors displayed the characteristic white light emanation resulted from blue and yellow emission owing to 4F9/2→6H15/2 (450-525 nm) and 4F9/2→6H13/2 (525-650) transitions, respectively. With the doping of 1.5 mol% amount of Dy3+ ions in Y2(1-x)Dy2xZr2O7 powders showed maximum photoluminescence emission, above which intensity was quenched due to dipole-dipole interactions. In addition, Y1.97Dy0.03Zr2O7 nanopowders exhibit CIE colour coordinates (0.2605, 0.3145) residing in white region. The closeness of this value to the white emission coordinates of the National Television System Committee (NTSC) endorsed Y2(1-x)Dy2xZr2O7 nanophosphors as fascinating candidate for displays and white light emitting diodes.

Enhancement of intrinsic green emission in phase pure ZnO

The Phase pure wurtzite structured ZnO phosphor was prepared by sintering three different precursors viz. zinc acetate, zinc nitrate, and ZnO at 800 °C, 900 °C, and 1000 °C in a reducing atmosphere for 1 h. The prepared ZnO phosphor samples were characterized by powder X-ray diffraction and the Rietveld refinement analysis in order to study their structural information that confirms their wurtzite hexagonal phase. Scanning electron microscopy (SEM) pictures exhibited irregular spherical morphology with an average particle size between 1 and 3 μm. The corresponding EDAX spectrum confirmed the presence of Zn and O species. Dependence of sintering temperature on the photoluminescence (PL) properties of ZnO samples and their enhancement on deep-level emission were studied. Deep level green emission around 505 nm was observed for the ZnO samples sintered in the reducing atmosphere without adding any impurities. Among three samples, the maximum PL emission intensity and better CIE colour coordinates under 380 nm excitation were obtained for the ZnO sintered at 900 °C and 1000 °C. Maximum Entropy Method (MEM) were used to determine the electron distributions in the unit cell which supports the PL investigation.

Comparative study of the luminescence of Bi doped LaOCl and LaOBr phosphor powders

In this work, Bi3+ doped lanthanum oxyhalides (LaOX, X = Cl or Br) were prepared via the solid-state reaction method in order to compare their photoluminescence (PL) properties and stability. Their structure and morphology were assessed using X-ray diffraction and scanning electron microscopy, while the annealing temperature and doping concentration were optimized for maximum PL emission intensity. The 3P1 → 1S0 emission transitions of Bi3+ ions in LaOCl:Bi and LaOBr:Bi were located in the ultraviolet at 344 nm and 358 nm, for excitation at 266 nm and 273 nm, respectively. The red-shift and lower intensity emission of LaOBr:Bi compared to LaOCl:Bi was attributed to the stronger nephelauxetic effect in the bromide host. Although LaOCl:Bi was not completely stable when stored exposed to the atmosphere for several months, LaOBr:Bi was significantly less stable and also showed accelerated degradation when exposed to a 254 nm UV lamp. Although previous reports for scintillators and upconversion phosphors based on these hosts have found LaOBr to be preferable, direct comparison of PL for these materials doped with Bi3+ ions showed that the LaOCl host was superior.

Comparisons of the synthesis and photoluminescence properties of ZnO nanorods under different solution concentrations

In this study, the sol–gel method was used to prepare ZnO seed layer for synthesizing ZnO nanorods, and we would investigate the effects of different Zn(CH3COO)2 and C6H[Formula: see text]N4 concentrations on the synthesized characteristics of ZnO nanorods. First, the ZnO gel was dipped on the surface of the [Formula: see text]-type [Formula: see text] wafer as a seed layer. Then, the hydrothermal method with different Zn(CH3COO)2 and C6H[Formula: see text]N4 concentrations as precursors was used to synthesize ZnO nanorods on [Formula: see text]-type [Formula: see text] wafer. X-ray diffraction (XRD) pattern, focused ion beam-field emission scanning electron microscopy (FIB-FESEM) and photoluminescence (PL) spectrometry were employed to observe and analyze the crystal properties, surface morphologies, and optical properties of the prepared ZnO seed layer and synthesized ZnO nanorods. [Formula: see text]C and 60 min were used as the synthesis temperature and time, and we found that Zn(CH3COO)2 and C6H[Formula: see text]N4 concentrations had an apparent effect on the height, diameter, total surface area, total volume, density, and PL property of ZnO nanorods. The maximum PL emission intensity of ZnO nanorods presented in the samples with Zn(CH3COO)2 and C6H[Formula: see text]N4 concentrations of 0.2 M. The results of XRD patterns suggest that ZnO nanorods have the property of [Formula: see text]-axis preferred orientation. We showed that the different Zn(CH3COO)2 concentrations had large effects on the average height, average diameter, aspect ratio, total surface area (S, nm[Formula: see text], total volume (V, nm[Formula: see text], S/V ratio, and PL property of ZnO nanorods.

Investigations of a Statistical and Analytical Method to Find the Relationship between the Morphological and Optical Properties of ZnO Nanoflower Arrays

In this study, a sapphire substrate with a patterned concave structure was used to prepare ZnO film/A-B glue, and the ZnO film/A-B glue with a patterned convex matrix was transferred onto a silicon wafer using the lift-off technology as the seed layer. Then, the hydrothermal method with different Zn(CH3COO)2 and C6H12N4 concentrations as precursors was used to synthesize ZnO nanoflower arrays on the patterned convex ZnO seed layer. XRD pattern, FESEM, FIB, and photoluminescence (PL) spectrometry were employed to observe and analyze the properties of the synthesized ZnO nanoflower arrays. When Zn(CH3COO)2 and C6H12N4 concentrations were 0.01, 0.02, 0.03, and 0.04 M, the average heights of the ZnO nanorods in the ZnO nanoflower arrays were 993, 1500, 1550, and 1650 nm, the average diameters of the ZnO nanorods were 50, 90, 105, and 225 nm, and the aspect ratios (H/D) of the ZnO nanorods were 19.9, 16.7, 14.8, and 7.33, respectively. A simple statistical and analytical method was investigated to estimate the densities (number of nanorods) of the ZnO nanoflower arrays in one 1 μm × 1 μm area. The total surface area (S) of the ZnO nanoflower arrays first increased from 5.05 × 106 and then reached a maximum value of 1.20 × 107 nm2 as Zn(CH3COO)2 and C6H12N4 concentrations increased from 0.01 to 0.02 M. For the systhesized ZnO nanoflower arrays, as the Zn(CH3COO)2 and C6H12N4 concentrations increased from 0.01 to 0.04 M, their total volume (V) increased from the 6.23 × 107 to 5.90 × 108 nm3 and the S/V ratio decreased from 8.10 × 10–2 to 1.84 × 10–2. We found that ZnO nanoflower arrays with Zn(CH3COO)2 and C6H12N4 concentrations of 0.2 M presented the maximum PL emission intensities. The calculated S/V ratios and X-ray photoelectron spectroscopy analyses are used to discuss the reasons for these results.

Carbon Dots from Turnip Juice: Synthesis, Characterization and Investigation of pH-Dependent Optical Properties

In this study, carbon dots (CDs) were synthesized using a simple one-pot hydrothermal method by using turnip juice as carbon source. The water-soluble nontoxic carbon dots were obtained after reaction. The structural and optical properties of as synthesized CDs were elucidated by X-ray diffraction (XRD), Raman, Fourier Transmission Infrared (FTIR), UV–Vis absorption and Photoluminescence (PL) spectroscopy. A contour plot of the excitation dependent PL spectra of the turnip juice derived CDs and PL emission spectra in 3D color map were plotted. The maximum PL emission was found at 434 nm when excited at 364. The pH dependent luminescence properties of the CDs were investigated from pH 2-12 range in phosphate buffer solution (PBS). The resulting CDs can be evaluated in a variety of application areas, from anti-counterfeiting to bioimaging.

Structural, optical and luminescence properties of BaLaGa3O7: x Eu3+ ceramic phosphors

The undoped and Eu3+ doped BaLaGa3O7 ceramic phosphors have been prepared using solid state reaction technique. The structural studies have been done using X-ray Diffraction (XRD) and Fourier transform infra-red (FTIR) technique and the surface morphology analysis using Field emission scanning electron microscope (FESEM). The elemental analysis has been carried out using Energy Dispersive X-ray spectroscopy (EDX) and elemental mapping. XRD study reveals that all the prepared phosphors are single phase with tetragonal crystal structure. The FESEM and EDX spectra confirm the single phase nature of the phosphors. FTIR technique identifies the various vibrational modes present in the prepared phosphors. The UV–Visible analysis provides the absorption region and band gap energies of undoped as well as doped BaLaGa3O7 phosphors. The photoluminescence (PL) excitation spectra consist of sharp excitation peaks of Eu3+ ions at 374 and 394 nm. The emission spectra corresponding to excitation wavelengths of 374 and 394 nm have been carried out. Maximum PL emission is obtained for excitation at 374 nm and it provides excellent orange red emission. The decay profile of BaLaGa3O7:xEu3+ phosphors have been carried out. The mechanoluminescence (ML) property of the doped phosphors reveals good ML emission without any pre irradiation. The information about the trap depth parameters and charge carriers in the 1 kGy irradiated BaLaGa3O7 phosphor has been studied using the thermoluminescence (TL) glow curves. The BaLaGa3O7 phosphor is having kinetics of first order with activation energy 1.107 eV.

Synthesis and Structure-Photophysics Evaluation of 2-N-Amino-quinazolines: Small Molecule Fluorophores for Solution and Solid State.

2-N-aminoquinazolines were prepared by consecutive SN Ar functionalization. X-ray structures display the nitrogen lone pair of the 2-N-morpholino group in conjugation with the electron deficient quinazoline core and thus representing electronic push-pull systems. 2-N-aminoquinazolines show a positive solvatochromism and are fluorescent in solution and in solid state with quantum yields up to 0.73. Increase in electron donor strength of the 2-amino substituent causes a red-shift of the intramolecular charge transfer (ICT) band (300-400 nm); whereas the photoluminescence emission maxima (350-450 nm) is also red-shifted significantly along with an enhancement in photoluminescence efficiency. HOMO-LUMO energies were estimated by a combination of electrochemical and photophysical methods and correlate well to those obtained by computational methods. ICT properties are theoretically attributed to an excitation to Rydberg-MO in SAC-CI method, which can be interpreted as n-π* excitation. 7-Amino-2-N-morpholino-4-methoxyquinazoline responds to acidic conditions with significant increases in photoluminescence intensity revealing a new turn-on/off fluorescence probe.

P‐179: Design and Synthesis of Blue Thermally Activated Delayed Fluorescent Emitter with Strong PyCN Acceptor and Multi Donors

A thermally activated delayed fluorescence (TADF) emitter of 234CzPyCN was synthesized to study the effect of strong acceptor (PyCN) and strong multi donors on the TADF properties. Electrical and Photophysical properties of the TADF emitters were characterized by the electron donating and accepting strength of the molecule. The material was designed by uniting multiple carbazoles which are substituted at ortho, meta, and para positions relative to the PyCN that is applied as electron accepting unit. Energy band gap between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) was measured to be 2.97 eV. The maximum photoluminescence emission peak of 234CzPyCN was 479 nm. 234CzPyCN device presented maximum external quantum efficiency of 20.8% with a CIE color coordinate of (0.18, 0.37).

High-Efficiency Diphenylpyrimidine Derivatives Blue Thermally Activated Delayed Fluorescence Organic Light-Emitting Diodes.

Organic light-emitting diodes with thermally activated delayed fluorescence emitter have been developed with highly twisted donor–acceptor configurations and color-pure blue emitters. Synthesized 4-(4-(4,6-diphenylpyrimidin-2-yl)phenyl)-10H-spiro[acridine-9,9′-fluorene] (4,6-PhPMAF) doped device with spiroacridine as a donor unit and diphenylpyrimidine as acceptor exhibits the device characteristics such as the luminescence, external quantum efficiencies, current efficiencies, and power efficiencies corresponding to 213 cd/m2, 2.95%, 3.27 cd/A, and 2.94 lm/W with Commission International de l'Eclairage (CIE) coordinates of (0.15, 0.11) in 4,6-PhPMAF-doped DPEPO emitter. The reported 10-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-10H-spiro[acridine-9,9′-fluorene] (2,6-PhPMAF) doped device exhibit high device performance with 1,445 cd/m2, 12.38%, 19.6 cd/A, and 15.4 lm/W, which might be originated from increased internal quantum efficiency by up-converted triplet excitons to the singlet state with relatively smaller ΔEST of 0.17 eV and higher reverse intersystem crossing rate (kRISC) of 1.0 ×108/s in 2,6-PhPMAF than 0.27 eV and 3.9 ×107/s in 4,6-PhPMAF. Despite low performance of 4,6-PhPMAF doped device, synthesized 4,6-PhPMAF has better color purity as a deep-blue emission with y axis (0.11) than reported 2,6-PhPMAF with y axis (0.19) in CIE coordinate. The synthesized 4,6-PhPMAF has higher thermal stability of any transition up to 300°C and decomposition temperature with only 5% weight loss in 400°C than reported 2,6-PhPMAF. The maximum photoluminescence emission of 4,6-PhPMAF in various solvents appeared at 438 nm, which has blue shift about 20 nm than that of 2,6-PhPMAF, which contributes deep-blue emission in synthesized 4,6-PhPMAF.

Comparative Analysis of the Effects of Upconversion Nanoparticles on Normal and Tumor Brain Cells.

Glioma is the most aggressive type of brain tumors encountered in medical practice. The high frequency of diagnosed cases and risk of metastasis, the low efficiency of traditional therapy, and the usually unfavorable prognosis for patients dictate the need to develop alternative or combined approaches for an early diagnosis and treatment of this pathology. High expectations are placed on the use of upconversion nanoparticles (UCNPs). In this study, we have produced and characterized UCNPs doped with the rare-earth elements ytterbium and thulium. Our UCNPs had photoluminescence emission maxima in the visible and infrared spectral regions, which allow for deep optical imaging of tumor cells in the brain. Moreover, we evaluated the toxicity effects of our UCNPs on a normal brain and glioma cells. It was revealed that our UCNPs are non-toxic to glioma cells but have a moderate cytotoxic effect on primary neuronal cultures at high concentrations, a condition that is characterized by a decreased cellular viability and changes in the functional metabolic activity of neuron-glial networks. Despite the great potential associated with the use of these UCNPs as fluorescent markers, there is a need for further studies on the rate of the UCNPs accumulation and excretion in normal and tumor brain cells, and the use of their surface modifications in order to reduce their cytotoxic effects.

Design Strategy of Decorating Phenylcarbazole with a Donor and Acceptor for Blue-Shifted Emission in Thermally Activated Delayed Fluorescent Emitters.

A series of blue thermally activated delayed fluorescent (TADF) emitters of 1''-(4,6-diphenyl-1,3,5-triazin-2-yl)-9,9''-diphenyl-9H,9''H-3,3':9',4''-tercarbazole (TrzCz1) and 3',6'-di-tert-butyl-1-(4,6-diphenyl-1,3,5-triazin-2-yl)-9-phenyl-9H-4,9'-bicarbazole (TrzCz2) were synthesized through a molecular design approach to decorate phenylcarbazole with a donor and an acceptor. The 1- and 4-positions of the phenylcarbazole core were modified with a diphenyltriazine acceptor and a bicarbazole or tert-butylcarbazole donor, respectively, through a synthetic strategy to introduce Br at the 1-position and F at the 4-position. The TrzCz1 and TrzCz2 emitters showed maximum photoluminescence emission bands at λ=443 and 433 nm, which were blueshifted relative to those of the corresponding TADF emitters with the same donor and acceptor, respectively. In the device application, the TrzCz1 emitter showed a maximum external quantum efficiency of 22.4 %, with a color coordinate of (0.16, 0.21), and the TrzCz2 emitter showed a maximum external quantum efficiency of 9.9 %, with a color coordinate of (0.14, 0.09). This work proved that the design strategy of decorating phenylcarbazole with a donor and an acceptor is effective at blueshifting the emission of TADF emitters.

P‐173: Engineering of Linker Unit for Blue Thermally Activated Delayed Fluorescent Organic Light‐Emitting Diodes

A series of thermally activated delayed fluorescence (TADF) emitters of TrzCz1 and TrzCz2 are synthesized to study the effect of linker engineering on the TADF properties. Photophysical and electrical properties of TADF emitters were characterized by the electron donating strength of the molecule by integrating biscarbazole and t‐butylcarbazole electron donating units and triazine electron withdrawing unit. Energy bandgap between the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital (LUMO) was tuned by changing the electron donating strength of the molecule. t‐butylcarbazole based molecule TrzCz2 (0.13 eV) showed smaller singlet‐triplet energy gap than TrzCz1 (0.20 eV), and the maximum photoluminescence emission peaks of TrzCz1 and TrzCz2 were 443 and 433nm. TrzCz1 device showed maximum external quantum efficiency of 22.4% with a CIE color coordinate of (0.17, 0.28) and TrzCz2 showed maximum external quantum efficiency of 9.9% with a CIE color coordinate of (0.15, 0.09)

Effect of europium loading on the photoluminescence property of europium incorporated 3D-Mesoporous silica

Here, for the first time, europium was incorporated into the open-structure three-dimensional mesoporous siliceous material. Samples with different loadings of europium were synthesized through one-step hydrothermal treatment based on sol-gel technique. The prepared samples were characterized by different characterization techniques and the results showed the formation of isolated trivalent europium ions in silica matric at low loading samples. However, at high loading samples, nanoparticles of europium III oxide, with an average size of 5–10 nm size, were detected inside the pores of mesoporous silica matrix. The photoluminescence property of the prepared samples was investigated at two different excitation wavelengths of 393 nm and 466 nm. The maximum photoluminescence emission intensity peaks was observed at approximately 614 nm at the two-excitation wavelength. The intensity of emission peak for the 614 nm was also found to be enhanced with increasing the loading of europium ions, this signify that europium acts as a good luminescent activator for red phosphor.

Synthesis and properties of blue-light-emitting Oligo(fluorene-co-dibenzothiophene-S,S-dioxide)s

An effective synthetic route for preparation of oligo(fluorene-co- dibenzothiophene-S,S-dioxide)s (trimer SOF2, pentamer SOF4, heptamer SOF6 and nonamer SOF8) based on meta- or para-linked dibenzothiophene-S,S-dioxide (SO) unit as the core was developed by convergence method, for which the intermediates unilateral boric acid esters were prepared by one-step palladium-catalysed Suzuki cross-coupling reaction. The resulting oligomers exhibited excellent thermal stability with thermal decomposition temperature exceeding 415 °C, and high photoluminescent quantum yield in the solid state (52–81%). The UV–vis absorption and photoluminescence emission maxima of the oligomers exhibited gradual bathochromic shifts from the trimer to the nonamer, approaching those of the previously reported polymer PFSO10 containing 10 mmol% of the SO unit in the polyfluorene backbone, demonstrating the similar photophysical properties of the nonamer SOF8 and polymer PFSO10. The highest occupied molecular orbital energy level gradually decreased and the lowest unoccupied molecular orbital energy level steadily increased from the trimer SOF2 to the nonamer SOF8. The obtained oligomers displayed pure blue-light emission with the maximal emission peaked at about 440 nm and superior EL spectral stability compared with PFSO10 upon varying the current density from 100 mA cm−2 to 500 mA cm−2, in addition to more balanced hole and electron fluxes. With the device configuration of ITO/PEDOT:PSS/oligomer/CsF/Al, a maximum luminous efficiency of 2.75 cd A−1 with Commission Internationale de l’Eclairage (CIE) coordinates of (0.16, 0.15) was obtained for the device based on 37SOF8. The efficiency increased by 88% compared with the device based on 37PFSO10 (1.46 cd A−1). A similar enhancement in efficiency was also achieved for the device based on 28SOF8. These results indicate that the obtained oligomers are very promising candidates for structurally well-defined blue-light- emitting materials with high efficiency and reproducibility.