Commision Internationale De l'Eclairage Research Articles

Probing multifunctional applications of LiCa2Mg2V3O12: Sm3+ phosphor using Judd-Ofelt analysis and dual mode non-contact optical thermometry

LiCa2Mg2V3O12:Sm3+ phosphors have been prepared by solid state method and analysed by X-ray diffraction, EDX-elemental mapping, UV–VIS-NIR spectroscopy, photoluminescence (PL) and temperature dependent photoluminescence (TDPL). The absorption spectra analysis using Judd-Ofelt theory provides the intensity parameters and manifest the covalent nature of Sm-O bond. The PL spectra monitored at 338 nm excitation exhibits emission peaks of Sm3+ at 567, 617 and 651 nm in addition to the broad band emission of LiCa2Mg2V3O12 host. The Commision Internationale deL’Eclairage (CIE) coordinates, correlated color temperature (CCT) and color rendering index (CRI) values elucidate the efficient yellow emission of phosphors. The radiative parameters are evaluated and have outrageous branching ratio and cross section that aids in visible laser applications. The optical thermometry of phosphor is carried out by utilizing FIR method through selecting spectral modes 6H5/2/VO43-, 6H7/2/VO43- and 6H9/2/ VO43-. The mode 6H9/2/ VO43- have higher absolute sensitivity (Sa) and relative sensitivity (Sr) values of 0.4418 K−1 and 1.6079% K−1. The temperature resolution of modes are 0.1633, 0.1677 and 0.1563 K respectively. The thermochromic study reveals the high chromaticity shift (Δs = 0.1869) of phosphor and the Sa(x) and Sr(x) values evaluated based on CIE coordinates are 0.0011 K−1 and 0.2407% K−1 respectively. The PL and TDPL characteristics of prepared phosphor suggest that it have multifunctional application in the fields of lasers, thermo-sensors, thermochromic displays and LEDs.

Cluster-based segmentation for tobacco plant detection and classification

Tobacco is one of the major economical crops in the agriculture sector. It is essential to detect tobacco plants using unmanned aerial vehicle (UAV) images for improved crop yield and plays an important role in the early treatment of tobacco plants. The proposed research work is carried out in three phases: In the first phase, we collect images from UAV’s and apply the French Commision Internationale de l'eclairage (CIE) L*a*b colour space model as pre-processing operations and segmentation. And then two prominent motion descriptors namely histogram of flow (HOF) and motion boundary histogram (MBH) are combined with the optimal histogram of oriented gradients (HOG) descriptor for exploring optimal motion trajectory and spatial measurements. And finally, the spatial variations with respect to the scale and illumination changes are incorporated using the optimal HOG descriptor. Here both dense motion patterns and HOG are refined using hierarchical feature selection using principal component analysis (PCA). The proposed model is trained and evaluated on different tobacco UAV image datasets and done a comparative analysis of different machine learning (ML) algorithms. The proposed model achieves good performance with 95% accuracy and 92% of sensitivity.

Synthesis, crystal structure, and luminescence properties of RbCaF3:Eu3+ orange-red emitting phosphors for white light emitting diodes

A series of novel orange-red emitting RbCaF3:0.05Eu3+ phosphors were synthesized by solid-state reaction technique. Phase formation and crystal structure of RbCaF3 were investigated through powder X-ray diffraction patterns and Rietveld refinement. Through X-ray photoemission spectroscopy, their composition and nature of oxidation states were determined. These fluoroperovskite phosphors are efficiently excited by near ultraviolet (n-UV-394 nm) and a corresponding sharp emission peak is exhibited at 590 nm. This peak can be attributed to the 5D0→7F1 transition of the magnetic dipole. A concentration quenching effect can be observed with increasing Eu3+ ion concentration. The Commision Internationale del'Eclairage (CIE) chromaticity coordinates (x = 0.5764, y = 0.4277) of the RbCaF3: 0.05Eu3+ phosphors excited at 394 nm. Thermally stimulated luminescence (TSL) was carried out and analyzed for the trap depth (E) and frequency factor values. The above results indicate that the RbCaF3:0.05Eu3+ can be a potential orange-red emitting phosphor for white light emitting diodes.

Electrogenerated Chemiluminescence and Electroluminescence of N-Doped Graphene Quantum Dots Fabricated from an Electrochemical Exfoliation Process in Nitrogen-Containing Electrolytes.

Artificial lighting sources are one of the most important technological developments for our modern lives; the search for cost-effective and efficient luminophores is therefore crucial to a sustainable future. Graphene quantum dots (GQDs) are carbon-based nanomaterials that exhibit exceptional optical and electronic properties, making them a prime candidate for a luminophore in a light-emitting device. Nitrogen-doped GQDs fabricated from a facile top-down electrochemical exfoliation process with a nitrogen-containing electrolyte in this report showed strong photoluminescent emission at 450 nm, and electrogenerated chemiluminescence at 660 nm in the presence of benzoyl peroxide as a coreactant. When introduced into solid-state light-emitting electrochemical cells, for the first time, the GQDs displayed a broad white emission centered at 610 nm, corresponding to Commision Internationale de l'eclairage (CIE) colour coordinates of (0.38, 0.36).

Saturated red phosphorescent Iridium(III) complexes containing phenylquinoline ligands for efficient organic light-emitting diodes

Saturated red iridium phosphors are strongly desired for application in organic light-emitting diodes (OLEDs). Most of the reported iridium complexes with 2-arylquinoline or its derivatives as cyclometalating ligands are orange-red phosphorescent with peak wavelength below 620 nm. Herein trifluoromethyl (CF3) or Fluorine (F) is introduced into the 6-site of quinoline ring to design and synthesize the cyclometalated ligands 2-phenyl-6-CF3/F-quinoline (CF3-phq or F-phq) and heteroleptic iridium complexes Ir(CF3-phq)2(acac) (Ir-1), Ir(CF3-phq)2(tmd) (Ir-2), Ir(F-phq)2(acac) (Ir-3) and Ir(F-phq)2(tmd) (Ir-4). Owing to the electron-deficient feature of CF3 and F, the electron affinity of these complexes are increased, the corresponding LUMOs are pulled downwards, and the phosphorescence of CF3-containing iridium complexes are saturated red with peaks at 627–632 nm in photoluminescence. At the same time, by varying the ancillary ligand from acetylacetonate (acac) to 2,2,6,6-tetrametylheptane-3,5-dionate (tmd), the emitting performance are dramatically improved. As a result, the Ir(CF3-phq)2(tmd) based red OLED realized pure red electroluminescence with Commision Internationale de L'Eclairage (CIE) coordinates of (0.67, 0.33) with a high brightness of 12695 cd m−2 and a maximum external quantum efficiency of 14.96%, respectively, which maintained as high as 9.62% at a practical luminance of 1000 cd m−2. This is the first example of saturated red iridium phosphors with structure modification at the 6-site of quinoline ring of 2-phenylquinoline ligand.

Phenazasiline/Spiroacridine Donor Combined with Methyl-Substituted Linkers for Efficient Deep Blue Thermally Activated Delayed Fluorescence Emitters

Phenazasiline, a sp3 hybridized silicon-bridged diphenylamine, is a promising donor moiety for deep-blue TADF emitters because of its deep highest occupied molecular orbital, high triplet level of 3.1 eV, and orthogonal connection with acceptor moieties. Herein, we report highly efficient deep-blue TADF emitters composed of phenazasiline donor and triazine acceptor combined with methyl-substituted phenylene linkers. As a series of methyl-substituted linker-based TADF emitters, we also synthesized spiroacridine donor-based sky-blue TADF emitters to study the effect of methyl-substituted linkers on the photophysical properties of TADF emitters. Deeper blue emissions of TADF emitters were obtained by substituting either one or two methyl groups at the phenylene linker of TADF molecules, and a small singlet-triplet gap below 0.2 eV was maintained for efficient reverse intersystem crossing. Organic light-emitting diodes (OLEDs) with spiroacridine-based TADF emitters, TTSA and TXSA, showed external quantum efficiencies (EQEs) of 27.9 and 20.7% with sky-blue emission of Commision Internationale de L'Eclairage (CIE) color coordinates of (0.158, 0.283) and (0.154, 0.251), respectively. With phenazasiline-based TADF emitters, TTAZ and TXAZ, highly efficient deep-blue OLEDs were realized with EQEs of 23.7 and 16% with improved CIE coordinates of (0.148, 0.158) and (0.148, 0.131), respectively.

Effect of Annealing Temperature on the Structure, Morphology and Photoluminescence Properties of MgAl2O4:0.1% Eu3+ Nanophosphor Prepared by Sol–Gel Method

Un-doped and 0.1% Eu3+-doped magnesium aluminate (MgAl2O4) nanomaterials were synthesized using the sol–gel method. The effects of annealing temperature (AT) from 600–1300°C on the crystal structure, morphology and photoluminescence properties were investigated. X-ray powder diffraction showed that below 650°C the structure consists of poorly crystalline and amorphous phases. A cubic phase structure corresponding to MgAl2O4 was formed at AT above 700°C. Generally, the crystallite sizes increased with an increase in AT. Energy-dispersive x-ray spectroscopy results confirmed the presence of the anticipated elementary composition. The scanning electron microscope and transmission electron microscope images suggested that the AT influenced the morphology, crystallite sizes and shape of the prepared phosphors. Photoluminescence (PL) results showed that the emissions peaks at 384 and 561 nm originate from defects located at different levels within the host material. The emission peaks at 561 nm, 581 nm, 594 nm, 618 nm, 655 nm and 701 nm were attributed to the (5D1 → 7F4) (5D0 → 7F0), (5D0 → 7F1), (5D0 → 7F2), (5D0 → 7F3) and (5D0 → 7F4) transitions of Eu3+ ion. Emission peaks from Eu3+ were observed to increase in intensity as the AT was increased. Luminescence enhancement was observed when increasing the AT to 650°C, while further increase lead to luminescence quenching. The Commision Internationale de l’Eclairage (CIE) coordinates results showed that the emission colour shift can be tuned from bluish to reddish by varying the AT.

Highly Efficient Phosphorescent Furo[3,2-c]pyridine Based Iridium Complexes with Tunable Emission Colors over the Whole Visible Range.

A series of highly efficient phosphorescent Ir complexes with tunable emission colors over the whole visible range have been designed and synthesized based on furo[3,2-c]pyridine ligand. By mainly varying the molecular structures of the C-chelated blocks, the emission maxima of these complexes can be obviously tailored from 477 to 641 nm while keeping the considerable photoluminescence quantum yields (PLQYs) (0.55-0.78 at wavelength of 475-560 nm and 0.10-0.34 at wavelength of 590-640 nm). Correspondingly, the phosphorescent organic light-emitting diodes (OLEDs) achieve high-performance greenish-blue, green, greenish-yellow, orange, red, and deep-red electrophosphorescence, revealing state-of-art external quantum efficiences (EQEs) of 20.0% (46.6 cd/A), 31.8% (89.0 cd/A), 19.9% (71.9 cd/A), 16.6% (38.9 cd/A), 12.0% (16.7 cd/A), and 8.5% (7.3 cd/A) as well as Commision Internationale de L'Eclairage (CIE) coordinates of (0.25, 0.48), (0.30, 0.58), (0.43, 0.54), (0.62, 0.37), (0.66, 0.32), and (0.70, 0.29), respectively. The results clearly demonstrate the great potential of furo[3,2-c]pyridine based phosphors used for full-color OLED displays.

Effect of annealing at different time intervals on the structure, morphology and luminescent properties of MgAl2O4:0.3% In3+ nanophosphor prepared by citrate sol-gel method

Indium-doped magnesium aluminate (MgAl2O4:03% In3+) spinel powders were prepared by citrate sol-gel method. The effect of annealing period (AP) at a fixed annealing temperature (800 °C) and dopant concentration (0.3% In3+) on the structure, particle morphology and photoluminescent properties of the powders were investigated. The X-ray powder diffraction (XRD) results showed that the crystalline quality and crystallite sizes of the powders were influenced by the AP. Doping with 0.3% In3+ did not influence the major crystal structure of the MgAl2O4 (host) material. The scanning electron microscope (SEM) image suggested that the AP influences the particle morphology of the nanophosphor. Transmission electron microscopy (TEM) image suggested that the crystallites sizes were in the region of 10 nm. The Photoluminescence (PL) results showed that the violet emission at 388 nm and green emission at 560 nm both originated from the host material and there was no evidence of any emission from the dopant (In3+). Increasing the AP up to 2 h lead to luminescence enhancement, while further increase in AP lead to luminescence quenching. The Commision Internationale de l’Eclairage (CIE) co-ordinates results showed that the emission colour of all samples was in the blue region and it was not tuned by varying the AP.

Iridium-containing polymers based on functionalized norbornenes as new efficient electroluminophores

The copolymer with carbazole and iridium-containing groups in the side chains (P1) and the terpolymer with additional organosilicon units (P2) were synthesized by the ring-opening metathesis polymerization (ROMP). The photoluminescence (PL) and electroluminescence (EL) properties of the synthesized polymeric materials were investigated. The iridium-containing terpolymer exhibited the most efficient EL characteristics: the maximum brightness is 1780 cd m−2 (21 V), the maximum current efficiency is 23.3 cd A−1 (13 V), and the maximum power efficiency is 6.4 lm W−1 (11 V). The color coordinates of the emission in the CIE (Commision Internationale de l’Eclairage) diagram (0.21, 0.71) correspond to the green color and remain virtually unchanged in the whole driving voltage range.

White organic electroluminescence from an exciplex based on the novel substituted aluminium quinolate complex

A saturated white organic light-emitting device was obtained from an exciplex mechanism by using a novel blue-green fluorescent tris(5-mesitylsulfone-8-hydroxyquinolato)aluminium(III), Al(MSq)3. Its absorption and photoluminescence appear at 3.25 eV and 2.56 eV. In photoluminescence, an exciplex, generated from an Al(MSq)3/TPD blend, was found at 2.10 eV. The lifetime of the Al(MSq)3/TPD blend is 22.3 ns, which is longer than that of either Al(MSq)3 or TPD. Due to the exciplex formation, the orange light generated can be combined with the blue-green light generated from Al(MSq)3 to achieve a white light emission. In an optimized electroluminescence device structure of [glass/ITO (200 nm)/PEDOT:PSS (75 nm)/blend (72 nm)/BCP (8 nm)/LiF (1 nm)/Al (200 nm)], the saturated white light emission was observed at Commision Internationale De L'Eclairage (CIE) coordinates of (0.35, 0.34). The EL spectrum of the device is also independent of the applied voltage. Its maximum brightness and efficiency are 26 cd m−2 at 15.2 V/67 mA cm−2, and 597 µW A−1 at 12.5 V/28 mA cm−2, respectively.

Colour change in pepper (Capsicum annuum) during storage

Powders of pepper were stored at ambient temperature, exposed to daylight The final quality was evaluated by measuring the extractable colour by the American Spice Trade Association (ASTA). Also, the possibility of using surface colour measurement, as a supplement to extractable colour measurement was investigated. The use of the chromatic attributes L, a and b, suggested by the Commision Internationale de l'Eclairage (CIE), i.e., of the CIELAB space, made it possible to find the correlation between ASTA and apparent colour of paprika.

Comparative Study of Anthocyanins in Tree Peony Flowers.

Flowers of the tree peony, Paeonia suffruticosa, and its interspecific hybrids with P. lutea, and P. delavayi, which originated in China and which were introduced by American and French breeders, were assayed for anthocyanins to trace their development.Petal hues of all Japanese cultivars (Paeonia suffruticosa) were distributed within the blue-red scope on Commision Internationale de l'Eclairage (CIE) (L*, a*, b*) color coordinate. Red-dish purple cultivars had high values of both blue and red, whereas pink or white cultivars had low values. Dark red or deep red-purple cultivars contained a large amount of anthocyanins in the petals, whereas pink or white cultivars contained a slight amount. Therefore, there was a high negative correlation between petal lightness (Hunter's L value) and petal anthocyanin contents.All dark red or deep red-purple Japanese cultivars contained 6 anthocyanins, peonidin 3, 5-diglucoside (Pn3G5G), peonidin 3-glucoside (Pn3G), cyanidin 3, 5-diglucoside (Cy3G5G), cyanidin 3-glucoside (Cy3G), pelargonidin 3, 5-diglucoside (Pg3G5G) and pelargonidin 3-glucoside (Pg3G). Vivid red cultivars lacked Cy3G/Cy3G5G but contained large amounts of Pg3G/Pg3G5G. Some pink cultivars lacked Pn3G and Pg3G as well as Cy3G/Cy3G5G.Of the 6 anthocyanins present in the Japanese cultivars, the Chinese cvs. of P. suffruticosa and P. suffruticosa var. spontanea generally lack Pg3G, which may account for the absence of the vivid red color.American and French interspecific hybrids between P. suffruticosa and P. lutea and P. delavayi lack Pg3G and Pg3G5G. The lack of pelargonidins gave rise to hybrids with crimson or scarlet flowers; but in the presence of a yellow chalcone, peonidin and cyanidin in some cultivars gave rise to orange or maroon flowers. The yellow pigment is inherited from the P. lutea and P. delavayi.