Photometric Efficiency Research Articles

Studying CdS:In green phosphor's impacts on white-light emitting diode with higher luminous flux

Abstract A lumen efficiency (LE) simulation model with the Monte Carlo method is introduced to the white-light-emitting diode devices that utilize the red LED (light-emitting diode) dyes instead of red-emitting phosphors (R-WLEDs). By simulating this model, the desirable spectrum-related indices and photometric efficiencies, which are adequate for superior chromatic consistency (or R f > 97), can be accomplished for R-WLEDs under the correlated color temperature (CCT) range of 5000–8000 K. The structure of the R-LED has LEDs in red and blue colors (650 nm and 448 nm) combined with phosphors possessing yellow and green emissions (586 nm and 507 nm). In comparison with pc-WLEDs (WLEDs operating with conversion phosphors) and QD-WLEDs (WLED devices with quantum dots), pc/R-WLED devices could present its outperformance to the others and become a promising way to achieve remarkable chromatic generation, particularly under the condition of small color temperature limit, and act as a substitute for the pc-WLED devices.

Analysis, evaluation and integration of modular natural illumination system using a rectangular Fresnel lens for high performance

Daylighting using natural illumination system (NILS) is gaining popularity due to transition to the renewable and non-conventional energy resources. In the proposed work, optomechanical design, numerical analysis, experimentation and integration of a modular Fresnel lens for NILS to effectively harness the sunlight is discussed. The modular and integrated design delivers uniform light at the receiving area of the daylight transportation system. This modular Fresnel lens is a combination of linear Fresnel lenses designed to offer a moderate concentration ratio to avoid hot spots. The distribution of solar radiation on the focal plane/entry section of the plastic optical fibre bundle (daylight transportation system) is simulated using the ray-trace technique for a lens system with a concentration ratio of 81. The irradiance distributions at the focal plane were found uniform with a radiometric and photometric transmission efficiency of 72.45% and 85.96%, respectively, for the lens element. The overall photometric transmission efficiency of the system with 10 m long plastic/acrylic optical fibre cable was found as 40.97%.

Hole-transporting materials based on diarylfluorene compounds containing different substituents: DFT simulation, spectroscopic characterization and applications in organic light emitting diodes

Three diarylfluorene derivatives with phenyl, biphenyl, and naphthyl fragments were synthesized and characterized as electroactive materials of high thermal stability, which can form amorphous layers with glass transition temperatures of 31–74 °C. Systematic analysis of diarylfluorene compounds in the framework of the molecular charge redistribution processes according to quantum chemistry simulations allows concluding that a partially broken π-conjugated system of the core is related to the rotation motion of substituents which effectively modified the π-conjugated properties of fluorene core. The low-molar-mass derivatives, previously tested as hole transporting (HT) materials, were used in bilayer electroluminescent organic light emitting diodes with Alq3 as the emitter. The device with the HT layer of 2,7-di(1-naphthyl)-9,9-diethylfluorene exhibited the best overall performance as turn-on voltage of 4.6 V; maximum photometric efficiency of 2.8 cd A−1; maximum brightness about 7760 cd m−2.

New structure hole transporting derivative for efficient organic light emitting devices

2,7-Di(4-biphenyl)-9,9-dihexylfluorene was synthesized by a multi-step synthetic rout. The material was characterized by proton nuclear magnetic resonance (1H NMR) spectroscopy, mass spectrometry, differential scanning calorimetry and thermogravimetric analyses. The electro-active derivative could form thin amorphous films and was tested as solution processed hole transporting layers in organic light- emitting diode with Alq3 as an emitter, which also has served as electron transporting material. The prepared electroluminescent device demonstrated low turn voltage of 3.2 V, a maximal photometric efficiency of 4.5 cd/A and maximum brightness exceeding 15600 cd/m2 .

Comparing Observed Stellar Kinematics and Surface Densities in a Low-latitude Bulge Field to Galactic Population Synthesis Models

Abstract We present an analysis of Galactic bulge stars from Hubble Space Telescope Wide Field Camera 3 observations of the Stanek window (l, b = [0.25, −2.15]) from two epochs approximately two years apart. This data set is adjacent to the provisional Wide-field Infrared Survey Telescope (WFIRST) microlensing field. Proper motions are measured for approximately 115,000 stars down to 28th mag in V band and 25th mag in I band, with accuracies of 0.5 mas yr−1 (20 km s−1) at I ≈ 21. A cut on the longitudinal proper motion μ l allows us to separate disk and bulge populations and produce bulge-only star counts that are corrected for photometric completeness and efficiency of the proper-motion cut. The kinematic dispersions and surface density in the field are compared to the nearby SWEEPS sight line, finding a marginally larger-than-expected gradient in stellar density. The observed bulge star counts and kinematics are further compared to the Besançon, Galaxia, and GalMod Galactic population synthesis models. We find that most of the models underpredict low-mass bulge stars by ∼33% below the main-sequence turnoff, and upwards of ∼70% at redder J and H wavebands. While considering inaccuracies in the Galactic models, we give implications for the exoplanet yield from the WFIRST microlensing mission.

Stokes polarimeter performance: general noise model and analysis.

We calculate the photometric Stokes parameter covariance matrices and SNRs estimated by polarimeters exposed to general noise distributions, such as mixed Poisson-Gaussian (PG) noise. The measurement model includes the effects of optical losses and detector quantum efficiency, enabling quantitative comparison of instruments that have different photometric efficiencies. We demonstrate this capability by comparing the performance of many common polarimeter configurations, including diattenuator-based systems, such as Azzam's four-detector polarimeter [Opt. Lett.10, 309 (1985)OPLEDP0146-959210.1364/OL.10.000309] and Kudenov's stacked photovoltaic polarimeter [Opt. Express24, 14737 (2016)OPEXFF1094-408710.1364/OE.24.014737]. Working with the full covariance matrix under mixed PG noise, we also show that instruments optimized under assumptions of Gaussian noise simultaneously exhibit optimal behavior under Poisson noise.

Polyethers containing 4-(carbazol-2-yl)-7-arylbenzo[c]-1,2,5-thiadiazole chromophores as solution processed materials for hole transporting layers of OLEDs

Two polyethers containing electroactive pendent 4-(carbazol-2-yl)-7-arylbenzo[c]-1,2,5-thiadiazole moieties have been synthesized by the multi-step synthetic route. Full characterization of their structures is presented. The polymers represent derivatives of very high thermal stability with initial thermal degradation temperatures of 425 °C and 431 °C. Glass transition temperatures of the amorphous materials were also very high and reached values of 154 °C and 163 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials of 5.84 eV and 5.93 eV. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter and electron transporting material. An electroluminescent device containing hole-transporting layer (HTL) of the polymer with electroactive 4-carbazolyl-7-phenylbenzo[c]-1,2,5-thiadiazole moieties exhibited turn on voltage of 6.2 V, maximum photometric efficiency of 2.5 cd/A and maximum brightness exceeding 300 cd/m2. The device containing HTL of the polymer with 4-carbazolyl-7-(1-naphtyl)benzo[c]-1,2,5-thiadiazole moieties demonstrated turn on voltage of 5.2 V, maximum photometric efficiency of 1.6 cd/A and maximum brightness exceeding 1500 cd/m2. The efficiencies were about 30–90% higher than that of the device containing widely used hole transporting layers of poly(9-vinylcarbazole).

Phenylethenyl substituted 10-alkylphenoxazines as new electroactive materials for organic light emitting diodes

Phenylethenyl substituted 10-alkylphenoxazines were synthesized by a multi-step synthetic route. The derivatives were characterized by thermo-gravimetric analysis, differential scanning calorimetry, electron photoemission and time of flight technique. The materials were found to show very high thermal stability having initial thermal degradation temperatures in the range of 338–354 °C. Glass transition temperatures of the low molar mass materials were in the rage of 41–49 °C. The electron photoemission spectra of thin layers of the derivatives showed ionization potentials in the range of 5.16–5.3 eV. Hole drift mobility in thin layers of these derivatives ranged from 6 × 10−4 cm2V−1s−1 to 4.5 × 10−3 cm2V−1s−1 at high electric fields at room temperature. The synthesized materials have been tested as hole transporting layers in electroluminescent bilayer organic light emitting diodes with tris(quinolin-8-olato)aluminium as an emitter. The device with hole transporting layer comprised of 3,7-di(2-phenylethenyl)-10-(2-ethylhexyl)phenoxazine exhibited the best overall performance with low turn-on voltage of 2.8 V, a maximum photometric efficiency of about 3 cd/A and maximum brightness of 2160 cd/m2. Taking the device at 1000 cd/m2, the photometric efficiency was increased by 25%, as compared with that of PEDOT:PSS-based device.

New electroactive polymers with electronically isolated 3,6,9-triarylcarbazole units as efficient hole transporting materials for organic light emitting diodes

Polyethers containing electronically isolated 3,6,9-triarylcarbazole moieties have been synthesized by the multi-step synthetic procedures. A polymer containing unsubstituted carbazole rings was also prepared for comparison of properties. Full characterization of the materials is presented. The new polymers represent materials of high thermal stability with initial thermal degradation temperatures exceeding 367 °C. The high glass transition temperatures of the amorphous materials were in the rage of 133–146 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials in the range of 5.52–5.6 eV. Hole-transporting properties of the electroactive materials were tested in the structures of organic light emitting diodes (OLEDs) with tris(quinolin-8-olato)aluminium as the green emitter and electron transporting material. The OLED devices in general exhibited rather low turn-on voltages of 3.2–4.2 V, high maximum brightness of 4910–7500 cd/m2 and luminous efficiency of 1.7–3.1 cd/A. It was confirmed that the devices containing the polymers with 3,6,9-triarylcarbazole moieties demonstrate considerably better OLED performance than that of device with polymer containing unsubstituted carbazole rings due to its higher ionization potential and accordingly worse hole injecting properties. The device containing hole-transporting layer of polymer with 3,6-di(1-naphthyl)-9-phenylcarbazole units exhibited the best overall performance with rather low turn on voltage of 4.4 V, maximum photometric efficiency exceeding 3.1 cd/A and maximum brightness of about 7500 cd/m2.

Fluorenes substituted with fluorophenyl, difluorophenyl or trifluorophenyl fragments as materials for organic light emitting diodes

ABSTRACT9,9-Diethylfluorenes substituted with two fluorophenyl, difluorophenyl or trifluorophenyl fragments were synthesized by the multi-step synthetic rout. The materials were characterized by 1H NMR spectroscopy, mass spectrometry, differential scanning calorimetry and thermogravimetric analyses. Some of the electro-active derivatives could form thin amorphous films and were tested as solution processed hole transporting layers in organic light- emitting diodes with Alq3 as the emitter and electron transporting material. Some of the electroluminescent devices demonstrated turn voltage of 5.5 V, a maximal photometric efficiency of about 1.0 cd/A and maximum brightness exceeding 960 cd/m2.

Polymers Containing Diphenylvinyl-Substituted Indole Rings as Charge-Transporting Materials for OLEDs

Monomers and polymers containing electronically isolated diphenylvinyl-substituted indole rings were synthesized and characterized by nuclear magnetic resonance (NMR) and mass spectroscopies as well as by gel permeation chromatography. The polymers represent amorphous materials with glass transition temperatures of 91–109°C and thermal decomposition starting above 307°C. Electron photoemission spectra of thin films of the synthesized polymers revealed ionization potentials of 5.54–5.58 eV. The synthesized polymers were tested as hole-transporting materials in simple electroluminescent organic light-emitting diode (OLED) devices with tris(quinolin-8-olato)aluminium (Alq3) as an emitter as well as an electron-transporting layer. A green OLED device containing a hole-transporting layer of poly[1-(2,3-epithiopropyl)-2-methyl-3-(2,2-diphenylvinyl)indole] exhibited the best overall performance with a driving voltage of 4.0 V, maximum photometric efficiency of 2.8 cd/A and maximum brightness of about 4200 cd/m2.

Polyethers with pendent phenylvinyl substituted carbazole rings as polymers for hole transporting layers of OLEDs

Polyethers containing pendent 3-(2-phenylvinyl)carbazole moieties have been synthesized by the multi-step synthetic routes. Full characterization of their structures is presented. The polymers represent materials of high thermal stability with initial thermal degradation temperatures exceeding 370°C. The glass transition temperatures of the amorphous materials were in the range of 56–658°C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials of about 5.6eV. Hole-transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter and electron transporting layer. The device containing hole-transporting layers of poly{9-[6-(3-methyloxetan-3-ylmethoxy)hexyl]-3-(2-phenylvinyl)carbazole} exhibited the best overall performance with a maximum photometric efficiency of about 4.0cd/A and maximum brightness exceeding 6430cd/m2.

Phenylvinyl-Substituted Carbazole Twin Compounds as Efficient Materials for the Charge-Transporting Layers of OLED Devices

Twin compounds containing two phenylvinyl-substituted carbazole rings were synthesized by multi-step synthesis. The compounds were characterized by thermogravimetric analysis, differential scanning calorimetry, and electron photoemission spectroscopy. The thermal stability of the materials was very high; initial thermal degradation temperatures were in the range 411–419°C. The glass-transition temperatures of the amorphous materials were in the range 74–119°C. Electron photoemission spectra of thin layers of the compounds revealed ionization potentials were in the range 5.05–5.45 eV. The hole-transporting properties of thin amorphous layers of the twin compounds were tested in organic light-emitting diodes with Alq3 as green emitter. The best overall performance was observed for a device based on the twin compound containing 3-[2-(4-methylphenyl)vinyl]carbazole groups; the turn-on voltage was 2.6 V, the maximum photometric efficiency 2.34 cd/A, and maximum brightness approximately 7380 cd/m2. At a brightness of 1000 cd/m2 the photometric efficiency was 23% higher than for a PEDOT:PSS-based device.

Polyethers containing 3,6-diarylcarbazolyl groups as polymeric materials for hole transporting layers of OLEDs

Several polyethers containing pendent 3,6-diarylcarbazolyl moieties have been synthesized by the multi-step synthetic routes. Full characterization of their structures is presented. The polymers represent materials of high thermal stability with initial thermal degradation temperatures exceeding 419 °C. The glass transition temperatures of the amorphous materials were in the range of 66–108 °C. The electron photoemission spectra of thin layers of the polymers showed ionization potentials in the range of 5.47–5.69 eV. Hole transporting properties of the polymeric materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter. The device containing hole transporting layers of the polymer with 3,6-di(4-biphenyl)carbazolyl moieties exhibited the best overall performance with a maximum photometric efficiency of about 2.3 cd/A and maximum brightness exceeding 2630 cd/m2.

Twin derivatives of fluorophenyl, difluorophenyl or trifluorophenyl substituted carbazoles as electroactive amorphous materials

Twin derivatives containing two 4-fluorophenyl, 3,5-difluorophenyl or 2,4,6-trifluorophenyl substituted carbazole rings were synthesized by the multi-step synthetic routes. Thermal properties and hole injecting/transport properties of the materials were examined by thermogravimetric analysis, differential scanning calorimetry, electron photoemission and time of flight techniques, respectively. Hole-transporting properties of thin amorphous layers of the derivatives were also tested in the structures of organic light emitting diodes (OLEDs) with Alq3 as the green emitter. The bilayer device based on a twin derivative composed of 3-(3,5-difluorophenyl) carbazol-9-yl blocks exhibited the best overall performance with a maximal photometric efficiency of about 2.1cd/A and maximum brightness of 560cd/m2. An analogous multilayer OLED with an additional PEDOT:PSS hole injecting layer demonstrated turn on voltage of 6.0V, maximum brightness of about 6200cd/m2 and maximal photometric efficiency of 3.4cd/A.

Ytterbium-doped glass-ceramics for optical refrigeration.

We report for the first time the characterization of glass-ceramics for optical refrigeration. Ytterbium-doped nanocrystallites were grown in an oxyfluoride glass matrix of composition 2YbF(3):30SiO(2)-15Al(2)O(3)-25CdF(2)-22PbF(2)-4YF(3), forming bulk glass-ceramics at three different crystalisation levels. The samples are compared with a corresponding uncrystalised (glass) sample, as well as a Yb:YAG sample which has presented optical cooling. The measured X-ray diffraction spectra, and thermal capacities of the samples are reported. We also report for the first time the use of Yb:YAG as a reference for absolute photometric quantum efficiency measurement, and use the same setup to characterize the glass and glass-ceramic samples. The cooling figure-of-merit was measured by optical calorimetry using a fiber Bragg grating and found to depend on the level of crystallization of the sample, and that samples with nanocrystallites result in higher quantum efficiency and lower background absorption than the pure-glass sample. In addition to laser-induced cooling, the glass-ceramics have the potential to serve as a reference for quantum efficiency measurements.

Electro-active oligomers containing pendent 3-phenylcarbazol-6-yl or 2-phenylfluoren-7-yl fragments as materials for OLEDs

Vinyl oligomers containing 3-phenyl-9-ethylcarbazol-6-yl or 2-phenyl-9,9-diethylfluoren-7-yl fragments were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The derivatives represent materials of high thermal stability with initial thermal destruction temperatures of 348°C and 332°C. The glass transition temperatures of the amorphous materials were 150°C and 139°C, respectively. The electron photoemission spectra of layers of the synthesized oligomers showed ionization potentials in a range 5.6–5.9eV. Hole-transporting properties of the materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter. The device containing hole transporting layers of oligomer with phenyl-9,9-diethylfluoren-7-yl fragments exhibited the best overall performance with a maximal photometric efficiency of about 1.9cd/A and maximum brightness of about 2150cd/m2. The efficiency was about 40% higher than that of a device containing hole transporting layers of poly(9-vinylcarbazole) (PVK).

Electroactive polymers containing pendant harmane, phenoxazine or carbazole rings as host materials for OLEDs

Polystyrenes containing electronically isolated harmane, phenoxazine or carbazole rings were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The new polymers represent amorphous materials of high thermal stability with glass-transition temperatures of 139–179 °C. The electron photoemission spectra of layers of the synthesized polymers showed ionization potentials of about 5.6–6.0 eV. The polymers were tested as host materials in phosphorescent green OLEDs with bis(2-phenylpyridine)(acetylacetonato)iridium(III) as the guest. The device based on polymer containing phenoxazine fragments exhibited the best overall performance with a turn-on voltage of 2.8 V, maximum photometric efficiency of about 17 cd/A and maximum brightness of 2920 cd/m2.

Orbital motion effects in astrometric microlensing

We investigate lens orbital motion in astrometric microlensing and its detectability. In microlensing events, the light centroid shift in the source trajectory (the astrometric trajectory) falls off much more slowly than the light amplification as the source distance from the lens position increases. As a result, perturbations developed with time such as lens orbital motion can make considerable deviations in astrometric trajectories. The rotation of the source trajectory due to lens orbital motion produces a more detectable astrometric deviation because the astrometric cross-section is much larger than the photometric one. Among binary microlensing events with detectable astrometric trajectories, those with stellar-mass black holes have most likely detectable astrometric signatures of orbital motion. Detecting lens orbital motion in their astrometric trajectories helps to discover further secondary components around the primary even without any photometric binarity signature as well as resolve close/wide degeneracy. For these binary microlensing events, we evaluate the efficiency of detecting orbital motion in astrometric trajectories and photometric light curves by performing Monte Carlo simulation. We conclude that astrometric efficiency is 87.3 per cent whereas the photometric efficiency is 48.2 per cent.

Electro-active polymers containing electronically isolated N-phenyl-N-naphtylamine fragments

Monomers and polymers containing electronically isolated N-phenyl-N-naphtylamine fragments were synthesized and characterized by NMR and IR spectroscopies as well as by gel permeation chromatography. The polymers represent amorphous materials with glass transition temperatures of 71–78°C and thermal decomposition starting at temperatures >320°C. The electron photoemission spectra of layers of the synthesized polymers showed ionization potentials close to 5.8eV. The synthesized materials have been tested as hole transporting layers in simple OLED devices with Alq3 as the emitter/electron transporting layer. The green devices containing hole transporting film of poly[N-(2,3-epoxypropyl)-N-phenyl-1-naphtylamine] exhibited the best overall performance with a driving voltage of 4.5V, maximum photometric efficiency of 3.6cd/A and maximum brightness of 2850cd/m2.