Phosphor System Research Articles

Catalytic Asymmetric Aza-Diels-Alder Reaction of Ketimines and Unactivated Dienes.

The enantioselective aza-Diels-Alder reaction is efficient for constructing chiral tetrahydropyridines, but the catalytic asymmetric aza-Diels-Alder reaction of ketimines with unactivated dienes is still a challenging topic. Herein, guided by computational screening, a highly enantioselective aza-Diels-Alder reaction of 2-aryl-3H-indol-3-ones with unactivated dienes was realized by using a B(C6 F5 )3 /chiral phosphoric acid catalyst system under mild conditions. The reaction has a broad scope with respect to both aza-Diels-Alder reaction partners and hence offers rapid access to an array of tetrahydropyridine derivatives with pretty outcomes (up to 99 % yield, >20:1 dr and 98:2 er). The reaction is very efficient: lowering catalyst loadings for the model reaction to 0.1 mol %, enantioselectivity is still maintained. The synthetic utility was confirmed by transformations of the products. DFT calculations provide convincing evidence for the interpretation of stereoselection.

49‐3: High Power Laser Phosphor Light Source Using a Scanning Mirror for Projectors

With the advancement of blue laser developments at low cost, laser diodes and laser diode arrays are getting popular in various light system from low power to very high power. This paper presents a stationary phosphor system in which the phosphor plate is not in motion and can be attached to heat sinks for efficient removal of heat for high power operations, which cannot be achieve easily when the phosphor material is coated onto a rotating wheel. The highest effective power density, limited by the available laser source and the current heat sinking, of over 301 W per sq. mm has been achieved and is expected to increase in the near future with higher power laser sources and improved heat sinking.

Artificial intelligence for detection of periapical lesions on intraoral radiographs: Comparison between convolutional neural networks and human observers

The aim of this study was to compare the diagnostic performance of convolutional neural networks (CNNs) with the performance of human observers for the detection of simulated periapical lesions on periapical radiographs. Ten sockets were prepared in bovine ribs. Periapical defects of 3 sizes were sequentially created. Periapical radiographs were acquired of each socket with no lesion and with each lesion size with a photostimulable storage phosphor system. Radiographs were evaluated with no filter and with 6 image filter settings. A CNN architecture was set up using Keras-TensorFlow. Separate CNNs were evaluated for randomly sampled training/validation data and for data split up by socket (5-fold cross-validation) and filter (7-fold cross-validation). CNN performance on validation data was compared with that of 3 oral radiologists for sensitivity, specificity, and area under the receiver operating characteristic curve (ROC-AUC). Using random sampling, the CNN showed perfect accuracy for the validation data. When data were split up by socket, the mean sensitivity, specificity, and ROC-AUC values were 0.79, 0.88, and 0.86, respectively; when split up by filter, they were 0.87, 0.98, and 0.93, respectively. For radiologists, the values were 0.58, 0.83, and 0.75, respectively. CNNs show promise in periapical lesion detection. The pretrained CNN model yielded in this study can be used for further training on larger samples and/or clinical radiographs.

Palladium mediated one-pot synthesis of 3-aryl-cyclohexenones and 1,5-diketones from allyl alcohols and aryl ketones.

One-pot synthesis of Robinson annulated 3-aryl-cyclohexenones from allyl alcohols and ketones using palladium is reported. Long chain aliphatic or aryl substitutions at the C1 position of allyl alcohol result in the formation of 1,5-diketone products. This simple one-pot method avoids the use of highly electrophilic vinyl ketones.

Spectroscopy of Cr3+ activator: Tanabe−Sugano diagram and Racah parameter analysis

The Racah parameters in conjunction with the Sugano−Tanabe energy-level diagram are used as a means of describing the effects of electron−electron repulsion within the metal complexes in coordination chemistry. A determination of the excitation energies in the 3d3-configuration ions like Cr3+ and Mn4+ is possible from a set of Racah (B and C) and crystal-field splitting parameters (Dq), and vice versa. However, it is very difficult to exactly determine some excitation-state energies that leads to a large error in the Racah parameter determination. The present study focuses on this problem and proposes a new model that introduces an optional Racah parameter ratio of C/B ≡ r to make it possible without requiring an uncertain excited-state energy in the Racah parameter calculation. As a typical example, spectroscopic data of MgO:Cr3+ phosphor are investigated based on the present analysis model, where Cr3+ ions can be situated in cubic, tetragonal, and rhombic site of MgO lattice. The Racah parameters and related excited-state energies determined here are found to fall very well on each Tanabe−Sugano diagram curve (2Eg, 4T2g, 2T1g, 4T1g,a, 2T2g, and 2A2g). The present analysis model can be expanded to other 3d3-activated phosphor systems such as Mn4+ ion or fluoride hosts.

Effect of image acquisition parameters on the radiopacity of bulk-fill and nanocomposite resins

This study evaluated the radiopacity of 2 bulk-fill resins (SonicFill and Filtek Bulk Fill) and a nanocomposite (Filtek Z350 XT) resin compared with enamel, dentin, and aluminum as measured with different exposure parameters. Resin disks were radiographed together with a 1-mm human tooth section and an aluminum stepwedge, at exposure times of 0.2 and 0.32 s, and source-image (S-I) distances of 30 and 40 cm, using complementary metal oxide semiconductor (CMOS) and photostimulable phosphor systems. Grayscale values were measured using ImageJ software. Paired Student t tests were used to compare the effect of the receptor on grayscale values for each material. Analysis of variance was used to evaluate the effects of receptor, exposure parameters, and the resins on radiopacity. All resins exhibited greater radiopacity scores than enamel and were significantly different from each other. Filtek Z350 produced the lowest radiopacity values, whereas SonicFill produced the highest. The radiopacity values were higher on images acquired with CMOS receptors. Receptor type, exposure time, S-I distance, and material, as well as many interactions of these parameters, affected the radiopacity of the resins. The tested resins complied with ISO 4049. Exposure parameters and digital receptors affected their radiopacity.

P‐79: High Power Static Phosphor Plate Light Source for Digital Projections

As the costs of blue laser diodes and laser diode arrays are getting lower, laser excited phosphor systems will be used in areas that were not possible before. This paper presents a static, without a rotating phosphor wheel, high power laser excited phosphor system in which the phosphor plate has a very high damage threshold and droop threshold temperature. The highest power density, limited by the available laser source, of over 54 W per sq. mm has been achieved and is expected to increase in the near future with higher power laser sources, development of homogenizing and diffusing optics at the input, and micro and photonic structures at the output surfaces.

Do image enhancement filters in complementary metal oxide semiconductor and photostimulable phosphor imaging systems improve the detection of fractured endodontic instruments in periapical radiography?

The aim of this study was to evaluate the influence of image enhancement filters on detection of fractured endodontic instruments and on image noise and pixel intensity. In total, 26 mandibular molars (68 root canals), divided into 4 groups (presence/absence of root canal filling, and presence/absence of a fractured endodontic instrument) were radiographed by using a complementary metal oxide semiconductor (CMOS) and a photostimulable phosphor (PSP) system. Images with 4 enhancement filters (Sharpen UM, Edges All, BC Low, and BC High) were compared with nonfiltered images. The area under the receiver operating characteristic curve (Az), sensitivity, and specificity in detection of fractured instruments were compared for each imaging condition. Means and standard deviations (SD) to measure noise and changes in pixel intensity were calculated. Analysis of variance was used to analyze the data. There were no significant differences in Az, sensitivity, and specificity values between nonfiltered and filtered images in detection of instruments in root canals without and with root canal filling (P ≥ .360). SD was reduced by filters in CMOS but not PSP radiographs. Sharpen UM caused more changes in the mean values in both systems. Filters did not improve diagnostic performance in detecting instruments. Noise and pixel intensity were affected differently.

Faceta direta em resina composta como técnica restauradora minimamente invasiva para harmonização do sorriso

Introdução: São diversos os fatores que podem ocasionar problemas que afetam a estética oral e, entre eles, a ausência de harmonia entre a forma, o alinhamento e a disposição dos dentes anteriores se apresenta como um dos mais frequentemente observados, intensificado pelo escurecimento dental. Objetivo: Relatar um caso clínico, no qual foi utilizada a técnica operatória direta de facetas estéticas em resina composta como alternativa de tratamento restaurador para dentes anteriores, após o tratamento ortodôntico insatisfatório sob o ponto de vista estético. Relato de caso: Paciente jovem, 23 anos, gênero masculino, leucoderma, compareceu à Faculdade de Odontologia da UFRJ, queixando-se do seu sorriso, principalmente em relação à estética dos elementos dentários superiores anteriores. Ao exame clínico, observou-se uma discrepância na proporção do tamanho entre os incisivos centrais superiores e os incisivos laterais. O plano de tratamento consistiu na realização de facetas em resina composta, seguindo o protocolo de recomendação de ácido fosfórico e sistema adesivo, segundo as normas do fabricante. Conclusão: As facetas diretas em resina composta representam uma excelente opção, uma vez que os compósitos resinosos nanotecnológicos são capazes de mimetizar de forma natural, confiável e segura a estrutura dentária, através de uma técnica minimamente invasiva, permanecendo satisfatórias por um longo tempo e apresentando excelente custo benefício.

High-Brightness Red-Emitting Phosphor La3(Si,Al)6(O,N)11:Ce3+ for Next-Generation Solid-State Light Sources.

A novel high-brightness red-emitting phosphor, La3(Si,Al)6(O,N)11:Ce3+ (LSA), which can potentially be used as a laser-excited light source, is demonstrated. Laser-excited phosphor system has great potential for use as a white-light source, as it is orders of magnitude brighter than white LEDs. Although conventional yellow-green phosphors show excellent luminescent properties even under high-power laser excitation, red-emitting phosphors, which are essential to achieve a high color-rendering index and low color-temperature, show quantum efficiency quenching. This limits the output power in multiphosphor excitation systems. Ce3+ should successfully tolerate high-power excitation due to the shortest emission lifetime seen in rare-earth ions, caused by the 5d1-4f1 spin-allowed transition; however, a red-emitting Ce3+-doped phosphor of practical use has not been realized. LSA is described by the crystal-field modification of a yellow-emitting phosphor, La3Si6N11:Ce3+, with substitution of Al in Si sites. LSA shows 640 nm red emission together with tolerance for high-power excitation and thermal quenching, suggesting its significant potential for industrial applications that require ultrahigh brightness.

Enhancing thermometric performance via improving indicator signal in Bi3+-doped CaNb2O6:Ln3+ (Ln = Eu/Sm/Dy/Tb) phosphors

Currently, phosphor materials play an important role in designing noncontact remote optical thermometers. Although many approaches have contributed to improve thermometric performance of optical thermometers including optimization of host materials, size of nanoparticles, dopant type and concentration as well as excitation density and phonon energy engineering, the development of highly sensitive optical thermometric materials is still a challenge. Hence, we developed novel CaNb2O6 (CNO):Ln3+ (Ln3+ = Eu3+/Sm3+/Dy3+/Tb3+) phosphors as highly thermometric materials and proposed a novel strategy for further enhancing its thermometric performance via adding the intensity of indicator signal by co-doping Bi3+ ions in current phosphor system. Typically, the as-prepared CNO:Ln3+ phosphors present a broad blue emission around 470 nm originated from NbO6 octahedral groups and some respective emission lines derived from the characteristic f-f transitions of Ln3+ ions. Based on the diverse thermal quenching performance between blue emission and Ln3+ ions emission, the temperature sensitivities of CNO:Ln3+ were investigated in detail. Among them, the maximum relative sensitivity of CNO:Eu3+ sample reached 1.991% K−1 in the range of 298–448 K and remained 97% after five temperature cycles. Furthermore, an obvious discoloration was discovered during temperature cycle testing in CNO:Ln3+ samples under 254 nm UV lamp. Through doping Bi3+ ion, the strongest intensity of indicator signal is 24 folds that of CNO host. Correspondingly, the relative sensitivity of CNO:Bi3+, Eu3+ sample is obviously improved to 3.793% K−1 in the range of 298–523 K, owing to a larger range of the FIR value and a wider drop range of indicator signal. This work opens up an effective pathway to improving thermometric performance of optical thermometers by enhancing the intensity of indicator signal of employed phosphor materials.

Reimagining pH Measurement: Utilizing Raman Spectroscopy for Enhanced Accuracy in Phosphoric Acid Systems.

Measurement of pH is an integral component of chemical studies and process control; however, traditional pH probes are difficult to utilize in harsh or complex chemical systems. Optical spectroscopy-based online monitoring offers a powerful and novel route for characterizing system parameters, such as pH, and is well adapted to deployment in harsh environments or chemically complex systems. Specifically, Raman spectroscopy combined with chemometric analysis can provide an improved method of online p[H+] measurement. Multivariate curve resolution (MCR) analysis of Raman spectra can be utilized to determine speciation as a function of p[H+], and the MCR scores assigned to each species can be used to calculate p[H+]. Subsequent chemometric modeling can be used to correlate spectral response to p[H+]. This was demonstrated with phosphoric acid, a chemical system known to challenge traditional pH probes. Raman spectra exhibit clear changes with pH due to changing speciation, and chemometric modeling can be successfully utilized to correlate those fingerprints to p[H+]. With the use of this approach, p[H+] of the phosphoric acid system can be accurately measured without foreknowledge of system conditions such as ionic strength.

Effects of various side stream phosphorus recovery volume on the performance and microbial structures of mainstream biological system

ABSTRACT The effects of three side stream phosphorous recovery volume on the performance and microbial structure of biological phosphorous removal system were investigated. Results showed that the removal of COD and nitrogen had no significant impacts by side stream operation, but the removal of phosphorous were gradually enhanced with the increase in side stream volume (SSV). The secretion of extracellular polymeric substance (EPS) were variously promoted at the stripping period. However, with the increase in SSV, the inhibition on EPS and phosphorus-accumulating organisms (PAOs) phosphorous absorption were severe and the restoration were tougher. The high throughout 16S rRNA gene sequencing revealed the succession of microbial population were significantly effected by side stream operation. The relative abundances of PAOs reduced to 0.17%, 0.09% and 0.07% with 30%, 60% and 90% side stream operations, respectively. At the restoration period, the relative abundance could restore to 95.4%, 65% and 38% initial values, respectively. The relative abundances of glycogen-accumulating organisms were variously enhanced under various SSV conditions. In conclusion, at SSV of 60%, more abundant recovered phosphorous could be obtained and had slighter and reversible effects on activated sludges. The SSV of 60% was the applicable SSV for phosphorous recovery from the biological phosphorus removal system.

Multicomponent and multicatalytic asymmetric synthesis of furo[2,3-b]pyrrole derivatives: further insights into the mode of action of chiral phosphoric acid catalysts.

Multicomponent and multicatalytic reactions are those processes that try to imitate the way the enzymatic machinery transforms simple building blocks into complex products. The development of asymmetric versions of these reactions is a step forward in our dream of mirroring the exquisite selectivity of biological processes. In this context, the present work describes a new reaction for the asymmetric synthesis of furo[2,3-b]pyrrole derivatives from simple 3-butynamines, glyoxylic acid and anilines in the presence of a dual catalytic system, formed from a gold complex and a chiral phosphoric acid. Computations, aimed to understand the exceptional performance of 9-anthracenyl-substituted BINOL-derived phosphoric acid catalyst, suggest a fundamental role of non-covalent interactions being established between the catalyst and the reagents for the outcome of the multicomponent process. The linear geometry of the anthracenyl substituent along with the presence of an electron-withdrawing group in the aniline and an aromatic substituent in the 3-butynamine derivative seem to be key structural factors to explain the experimental results and, particularly, the high stereoselectivity.

Transition metal ion co-doped MgO–MgF2-GeO2:Mn4+ red phosphors for white LEDs with wider color reproduction gamut

Mn4+- activated non-rare-earth based red phosphors are excellent down conversion materials for phosphor-converted light-emitting diode (pc-LEDs) based solid-state lighting applications. However, the low quantum efficiency of Mn4+ activated red phosphors under InGaN based blue LED excitation hinders their use in phosphor-converted LEDs. To enhance the absorption at an excitation wavelength of around 420 nm in Mn4+-doped MgO–MgF2-GeO2 (MGF: Mn4+), which is a conventional red-emitting lamp phosphor, we doped MGF: Mn4+ phosphors with transition metal oxides (Sc2O3, Lu2O3, Y2O3, and La2O3) replacing MgO. When excited using 420 nm light, the absorption ratio of the synthesized phosphors with Sc2O3 (Sc-MGF:Mn4+) was 58% with an internal quantum efficiency (IQE) of 55% as compared to the 35% IQE of the pristine MGF-Mn4+ phosphor. White LEDs were fabricated using Sc-MGF-Mn4+ (red), and β-SiAlON:Eu2+ (green) on InGaN chips (λem = 450 nm) and their performance was compared to the optical performance of LEDs fabricated using K2SiF6:Mn4+ as the red phosphor. According to the National Television System Committee (NTSC) standard, the color reproduction coverage with an Sc-MGF:Mn4+ phosphor-loaded white LED was 121% by the International Commission on Illumination (CIE) 1976, and 80% by the BT.2020 standard. The coverages are 9% and 6% higher than the coverages of LEDs fabricated using K2SiF6:Mn4+ as the red phosphor according to the NTSC and BT.2020 standards, respectively. Our simple approach to enhance the IQE of Mn4+ activated phosphors by co-doping transition metal oxides can be extended to other Mn4+ activated phosphor systems for applications that require enhanced absorption, higher luminescent emission intensity, and a wider gamut of color reproduction.

Electronic Structure and Bonding of the Fastidious Species CN2 and CP2: A First-Principles Study.

The transient molecular species CN2 (CNN, NCN, c(yclic)-CN2) and CP2 (CPP, PCP, c(yclic)-CP2), along with the isoelectronic to CNN and isovalent to CPP, CCO, have been studied theoretically through the ab initio methodologies multireference configuration interaction (MRCI) and RCCSD(T) coupled with augmented correlation-consistent quintuple and sextuple basis sets. For the CNN, NCN, and c-CN2 molecules, the examined states are [X̃3Σ-, ã1Δ, b̃1Σ+, Ã3Π, and c̃1Π], X̃3Σg-, and X̃1A1, respectively. The analogous phosphorous system CPP has been studied theoretically for the first time. Our results show that the symmetries 3Σ-, 1Δ, and 1Σ+ are not stationary states; thence, the ground state of CPP is of 3Π symmetry and of similar electronic structure to that of the Ã3Π state of CNN. For most of the symmetries studied, we have constructed fully optimized potential energy profiles or "cuts" through the corresponding surfaces at the MRCI level of theory in an effort to follow the (valence) electronic distributions from the "selected" adiabatic species to equilibrium. Our numerical results are in excellent agreement with existing experimental data and previous, although limited, high-level ab initio calculations. Finally, it should be said that some of our findings like dissociation energies, permanent electric dipole moments, and bonding considerations are addressed for the first time.

Luminescence properties of reddish orange emitting BaLa2ZnO5:Sm3+ phosphor prepared by citric based sol-gel synthesis

A series of BaLa2ZnO5:Sm3+ phosphors were synthesized with the sol-gel technique. The crystalline structure of each sample was characterized by X-ray diffraction (XRD). Phase formation was investigated using scanning electron microscope (SEM). Photoluminescence studies revealed an efficient excitation of phosphors at near blue light (~410 nm), providing emission in the bright reddish-orange region (603 nm). Concentration quenching through multipolar interaction was observed in BaLa2ZnO5 phosphor system doped with 0.015 mol of Sm3+ concentration. The optimum phosphor showed prominent characteristics for application in white LEDs.

An anthropomorphic phantom representing a prematurely born neonate for digital x-ray imaging using 3D printing: Proof of concept and comparison of image quality from different systems

An anthropomorphic phantom for image optimization in neonatal radiography was developed, and its usability in optimizing image acquisition and processing demonstrated. The phantom was designed to mimic a patient image of a prematurely born neonate. A clinical x-ray (neonate <1 kg) taken with an effective dose of 11 µSv on a needle-crystal storage phosphor system was retrospectively selected from anonymized images as an appropriate template representing a standard case in neonatology imaging. The low dose level used in clinical imaging results in high image noise content. Therefore, the image had to be processed using structure preserving noise reduction. Pixel values were related to printing material thickness to result in a similar attenuation pattern as the original patient including support mattress. A 3D model generating a similar x-ray attenuation pattern on an image detector as a patient was derived accounting for beam hardening and perspective, and printed using different printing technologies. Best printing quality was achieved using a laser stereolithography printer. Phantom images from different digital radiography systems used in neonatal imaging were compared. Effects of technology, image processing, and radiation dose on diagnostic image quality can be assessed for otherwise identical anthropomorphic neonatal images not possible with patient images, facilitating optimization and standardization of imaging parameters and image appearance.

Novel multi-wavelength excitable single-component phosphor system for application in white-LEDs

A novel color-tunable phosphor of BaZnO2:xEu3+ (x = 0–20 mol%) has been successfully prepared via high-temperature calcination method using alkaline earth metal as the charge compensator. Uncommonly, BaZnO2:Eu3+ is a multi-wavelength excitable phosphor due to its wide absorption spectrum ranging 250–550 nm. It shows broad white (400–700 nm), orange (∼580 nm) and red (∼611 nm) photoluminescence (PL) under 370 nm, 395 nm and 467 nm excitations, respectively and were assigned to one or more 5D0→7FJ (J = 1 to 4) transitions of Eu3+ ion. An efficient energy transfer between Zn2+ and Eu3+ has been observed upon systematically increasing the concentration of Eu3+ ion. Scanning Electron Microscopy images indicated elongated rod-like structures with an average diameter of ∼20 nm. The chromaticity coordinates (x, y) were found to be positioned at white (0.33, 0.42), orange (0.51, 0.42) and red (0.65, 0.34) regions correspond to 370 nm, 395 nm and 467 nm excitations, respectively. The temperature-dependent luminescence spectrum of BaZnO2:Eu3+ under the excitation of 467 nm was also studied. It exhibited good thermal stability and a marginal drop in photoluminescence intensity by 4.29% at 150 °C was observed. The mathematical calculation of the activation energy was approximately 0.20 eV. The results indicate the suitability of the phosphor for LEDs applications, which is otherwise difficult to obtain in single-component system.

(Invited) The Impact of Defects on the Efficiency of Rare Earth Doped Oxides Under Vacuum Ultraviolet Excitation

Understanding the factors that govern efficient host-sensitized luminescence remains an important element in the development of more efficient luminescent materials. In a doped phosphor system, absorption of high energy photons leads to the creation of an electron-hole (e-h) pair in the host that must be captured by the dopant for emission to occur. While many materials have been developed for these applications, fundamental questions remain regarding the details of this energy transfer process. One aspect of research in this field that has not received much systematic attention is the study of the role various defects play in decreasing the efficiency of phosphors under host-sensitized excitation. The work presented here focuses on the effect of oxygen vacancies in rare earth doped YBO3 and YPO4, which are created via doping with Ca2+. Excitation and reflectance spectroscopy are combined to quantify the fraction of e-h pairs that are trapped by a dopant. The impact of oxygen vacancies depends on the particular rare earth present in the host, which is likely related to differences in the e-h trapping mechanism.