Commission Internationale d'Eclairage Research Articles

Enhancement of luminescence in white emitting strontium fluoride core @ calcium fluoride shell nanoparticles.

Synthesis of lanthanide-doped fluoride SrF2:3Dy and SrF2:3Dy@CaF2 nanoparticles with different ratios of core to shell (1:0.5, 1:1 and 1:2) has been carried out by employing ethylene glycol route. X-ray diffraction (XRD) patterns reveal that the structure of the prepared nanoparticles was of cubical shape, which is also evident in TEM images. The size of the nanoparticles for core (SrF2:3Dy) is found to increase when core is covered by shell (CaF2). It is also evident from Fourier transform infrared spectroscopy (FTIR) that ethylene glycol successfully controls the growth and acts as a shape modifier by regulating growth rate. In the photoluminescence investigation, emission spectra of SrF2:3Dy is found to be highly enhanced when SrF2:3Dy is covered by CaF2 due to the decrease of cross relaxation amongst the Dy3+-Dy3+ ions. Such type of enhancement of luminescence in homonanostructure SrF2:3Dy@CaF2 (core@shell) has not been studied so far, to the best of the authors’ knowledge. This luminescent material exhibits prominently white light emitting properties as shown by the Commission Internationale d’Eclairage (CIE) chromaticity diagram. The calculated correlate colour temperature (CCT) values for SrF2:3Dy, SrF2:3Dy@CaF2 (1:0.05), SrF2:3Dy@CaF2 (1:1) and SrF2:3Dy@CaF2 (1:2) are 5475, 5476, 5384 and 5525 K, respectively, which lie in the cold white region.Graphical abstractWhite light emitting homonanostructure material SrF2:3Dy@CaF2(core@shell).

Structural and luminescence studies on Dy3+ doped boro-phosphate glasses for white LED's and laser applications

The present work reports structural and luminescence studies on Dy3+ doped boro-phosphate glasses prepared with the chemical composition 51B2O3 + 10ZnO + 20Li2O + 9SrO + (10−x)P2O5 + xDy2O3 (where x = 0.1, 0.25, 0.5, 1 and 2 in wt%) by melt quenching technique. The presence of various stretching and bending vibrations of different borate and phosphate groups were identified from the FTIR spectral measurements. The Nephelauxetic ratios (β) and the bonding parameters (δ) calculated from the absorption spectra have been used to examine the bonding nature of the Dy–O bond in the prepared glasses. From the absorption spectra, optical band gap and Urbach's energy values were calculated to explore the electronic band structure. Judd-Ofelt (JO) theory have been employed to obtain the JO intensity parameters (Ω2, Ω4, Ω6) from the optical absorption spectra by using the experimental oscillator strength values. The luminescence spectra exhibit two intense emission bands at around 482 nm (blue) and 574 nm (yellow) corresponds to the 4F9/2 → 6H15/2 and 4F9/2 → 6H13/2 transitions respectively. The radiative parameters were evaluated from the emission spectra using the JO intensity parameters and refractive index values. The emission spectra for different pumping wavelengths were characterized through Commission International d'Eclairage (CIE) 1931 chromaticity diagram to explore its suitability for WLED applications. The decay profile of the prepared glasses exhibit single exponential behavior for lower Dy3+ ion concentration and turn to exhibit non-exponential behavior for higher Dy3+ ion content due to the energy transfer process which takes place between the donor and acceptor ions. The energy transfer mechanism between the nearby Dy3+ ions has been analyzed by fitting the non-exponential decay curves into IH model and the results were discussed and compared with the reported literature.

Low temperature fabrication and characterization of wurtzite structured ZnS quantum dots by chemical spray pyrolysis

Thin films of zinc sulfide quantum dots are prepared by chemical spray pyrolysis technique. This simple, low cost fabrication technique helps in the formation of uniform, well crystalline thin films. The low temperature formation of ZnS quantum dots with wurtzite phase is confirmed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Energy dispersive X-ray spectroscopy (EDX) is used for the elemental analysis of the prepared film. The various bonds present in the synthesized films are analysed using Fourier transform infrared spectroscopy (FTIR). The various applications of the ZnS thin films such as, an anti-reflector, window layer in photovoltaic devices and phosphor host material in display devices, are confirmed by the characterization tools like UV–vis–NIR spectroscopy and photoluminescence (PL). The film exhibits a blue emission with Commission International d’Eclairage (CIE) coordinates x=0.13, y=0.07.

Controlling the Chromaticity of Small‐Molecule Light‐Emitting Electrochemical Cells Based on TIPS‐Pentacene

This work demonstrates a novel proof‐of‐concept to implement pentacene derivatives as emitters for the third generation of light‐emitting electrochemical cells based on small‐molecules (SM‐LECs). Here, a straightforward procedure is shown to control the chromaticity of pentacene‐based lighting devices by means of a photoinduced cycloaddition process of the 6,13‐bis(triisopropylsilylethynyl) (TIPS)‐pentacene that leads to the formation of anthracene‐core dimeric species featuring a high‐energy emission. Without using the procedure, SM‐LECs featuring deep‐red emission with Commission Internationale d'Eclairage (CIE) coordinates of x = 0.69/y = 0.31 and irradiance of 0.4 μW cm−2 are achieved. After a careful optimization of the cycloaddition process, warm white devices with CIE coordinates of x = 0.36/y = 0.38 and luminances of 10 cd m−2 are realized. Here, the mechanism of the device is explained as a host–guest system, in which the dimeric species acts as the high‐energy band gap host and the low‐energy bandgap TIPS‐pentacene is the guest. To the best of the knowledge, this work shows the first warm white SM‐LECs. Since this work is based on the archetypal TIPS‐pentacene and the photoinduced cycloaddition process is well‐knownfor any pentacenes, this proof‐of‐concept could open a new way to use these compounds for developing white lighting sources.

White Light Emission from Vegetable Extracts.

A mixture of extracts from two common vegetables, red pomegranate and turmeric, when photoexcited at 380 nm, produced almost pure white light emission (WLE) with Commission Internationale d’Eclairage (CIE) chromaticity index (0.35, 0.33) in acidic ethanol. It was also possible to obtain WLE in polyvinyl alcohol film (0.32, 0.25), and in gelatin gel (0.26, 0.33) using the same extract mixture. The colour temperature of the WLE was conveniently tunable by simply adjusting the concentrations of the component emitters. The primary emitting pigments responsible for contributing to WLE were polyphenols and anthocyanins from pomegranate, and curcumin from turmeric. It was observed that a cascade of Forster resonance energy transfer involving polyphenolics, curcumin and anthocyanins played a crucial role in obtaining a CIE index close to pure white light. The optimized methods of extraction of the two primary emitting pigments from their corresponding plant sources are simple, cheap and fairly green.

Nanostructured zinc oxide thin film by simple vapor transport deposition

Zinc oxide (ZnO) nanostructures find applications in optoelectronic devices, photo voltaic displays and sensors. In this work zinc oxide nanostructures in different forms like nanorods, tripods and tetrapods have been synthesized by thermal evaporation of zinc metal and subsequent deposition on a glass substrate by vapor transport in the presence of oxygen. It is a comparatively simpler and environment friendly technique for the preparation of thin films. The structure, morphology and optical properties of the synthesized nanostructured thin film were characterized in detail by using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) and photoluminescence (PL). The film exhibited bluish white emission with Commission International d’Eclairage (CIE) coordinates x=0.22, y=0.31.

Sourcing limestone masonry for restoration of historic buildings, a spectroscopic pilot study

This study presents a combined Fourier transform (FT) mid-infrared, laser Raman and Commission internationale d’eclairage (CIE) L*a*b*system analysis of quarry-derived impure limestone and fallen masonry from a medieval listed building situated in the south east of England, to ascertain how spectroscopic information can be collectively employed to identify the most exacting possible replacement stone source.Data shows that subtle differences in [Al] and [Fe3+] octahedral and tetrahedral site occupancy in glauconite group clays registered in the mid-infrared [3530 cm−1/3620 cm−1] absorption ratio exerts some influence on L*Cab*hab*values. Increases in L*and Cabare associated with decreasing clay content. Theoverall weakness of correlations between infrared and visible range spectral attributes indicates multiple contributing sources to overall color. Evidence indicates that the degree of laser Raman induced background noise is related to the overall calcite content and that activators of fluorescence at 785 nmexcitation wave length may also contribute to rock color. The results are utilized to define closest matching quarry samples to the fallen masonry.

Electron beam induced and microemulsion templated synthesis of CdSe quantum dots: tunable broadband emission and charge carrier recombination dynamics

CdSe quantum dots (QDs) were synthesized by a rapid and one step templated approach inside the water pool of AOT (sodium bis(2-ethylhexyl) sulfosuccinate) based water-in-oil microemulsions (MEs) via electron beam (EB) irradiation technique with high dose rate, which favours high nucleation rate. The interplay of different experimental parameters such as precursor concentration, absorbed dose and values (aqueous phase to surfactant molar ratio) of MEs were found to have interesting consequences on the morphology, photoluminescence (PL), surface composition and carrier recombination dynamics of as-grown QDs. For instance, highly stable ultrasmall (∼1.7 nm) bluish-white light emitting QDs were obtained with quantum efficiency (η) of ∼9%. Furthermore, QDs were found to exhibit tunable broadband light emission extending from 450 to 750 nm (maximum FWHM ∼180 nm). This could be realized from the CIE (Commission Internationale d’Eclairage) chromaticity co-ordinates, which varied across the blue region to the orange region thereby, conferring their potential application in white light emitting diodes. Additionally, the average PL lifetime values could be varied from 18 ns to as high as 74 ns, which reflect the role of surface states in terms of their density and distribution. Another interesting revelation was the self-assembling of the initially formed QDs into nanorods with high aspect ratios ranging from 7 to 20, in correspondence with the values. Besides, the fundamental roles of the chemical nature of water pool and the interfacial fluidity of AOT MEs in influencing the photophysical properties of QDs were investigated by carrying out a similar study in CTAB (cetyltrimethylammonium bromide; cationic surfactant) based MEs. Surprisingly, very profound and contrasting results were observed wherein and η of the QDs in case of CTAB MEs were found to be at least three times lower as compared to that in AOT MEs.

Upconversion luminescence of Ho3+/Tm3+/Yb3+ tri-doped NaLa(MoO4)2 phosphors

The polycrystalline Ho3+/Tm3+/Yb3+ tri-doped NaLa(MoO4)2 phosphors were successfully synthesized by the simple solid-state reaction method. Under the laser excitation of a 980nm, Ho3+/Tm3+/Yb3+ tri-doped NaLa(MoO4)2 showed bright white upconversion (UC) emission visible to the naked eyes, which composes of blue emission at 475nm from Tm3+, green and red emissions at 540nm and 651nm from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped NaLa(MoO4)2 in the commission international de׳eclairage (CIE) chromaticity diagram could be controlled from cool to warm white color depending on Ho3+ and Tm3+ concentrations. The luminescent properties on Tm3+ and Ho3+ concentrations and UC mechanism based on laser pump power were discussed in detail.

Bright white-light emission from Ag/SiO2/CdS-ZnS core/shell/shell plasmon couplers.

Well-defined plasmon couplers (PCs) that comprise a Ag core overcoated with a SiO(2) shell with controlled thickness, followed by a monolayer of CdS-ZnS core-shell quantum dots (QDs) were synthesized to modify the emission from trap-rich CdS-ZnS QDs by adjusting the distance between the QDs and Ag nanoparticles (NPs). When the thickness of the SiO(2) shell was 10 nm, because the shell could effectively suppress the non-radiative energy transfer from the semiconductor QDs to the metal NPs and the localized surface plasmon resonance (LSPR) of the Ag NPs spectrally matched the emission peak of the CdS-ZnS QDs to bring about strong plasmon coupling, optimum enhancements of the surface state emission (SSE) (17 times) and band-edge emission (BEE) (4 times) were simultaneously realized and the SSE to BEE intensity ratio was increased to 55%. As a result, a bright white-light source with 1931 Commission Internationale d'Eclairage (CIE) chromaticity coordinates of (0.32, 0.34) was realized by the superposition of the two emissions. The experimental results from Ag/SiO(2)/CdSe-ZnS and the Ag/SiO(2)/CdS:Mn-ZnS core/shell/shell PCs indicated that suppressing the non-radiative decay rate (k(nr)) was the underlying mechanism for plasmon coupling fluorescence enhancement.

Effect of resin thickness on the microhardness and optical properties of bulk-fill resin composites.

ObjectivesThis study evaluated the effects of the resin thickness on the microhardness and optical properties of bulk-fill resin composites.MethodsFour bulk-fill (Venus Bulk Fill, Heraeus Kulzer; SDR, Dentsply Caulk; Tetric N-Ceram Bulk Fill, Ivoclar vivadent; SonicFill, Kerr) and two regular resin composites (Charisma flow, Heraeus Kulzer; Tetric N-Ceram, Ivoclar vivadent) were used. Sixty acrylic cylindrical molds were prepared for each thickness (2, 3 and 4 mm). The molds were divided into six groups for resin composites. The microhardness was measured on the top and bottom surfaces, and the colors were measured using Commission Internationale d'Eclairage (CIE) L*a*b* system. Color differences according to the thickness and translucency parameters and the correlations between the microhardness and translucency parameter were analyzed. The microhardness and color differences were analyzed by ANOVA and Scheffe's post hoc test, and a student t-test, respectively. The level of significance was set to α = 0.05.ResultsThe microhardness decreased with increasing resin thickness. The bulk-fill resin composites showed a bottom/top hardness ratio of almost 80% or more in 4 mm thick specimens. The highest translucency parameter was observed in Venus Bulk Fill. All resin composites used in this study except for Venus Bulk Fill showed linear correlations between the microhardness and translucency parameter according to the thickness.ConclusionsWithin the limitations of this study, the bulk-fill resin composites used in this study can be placed and cured properly in the 4 mm bulk.

Color-tunable mixed photoluminescence emission from Alq3 organic layer in metal-Alq3-metal surface plasmon structure.

This work reports the color-tunable mixed photoluminescence (PL) emission from an Alq3 organic layer in an Au-Alq3-Au plasmonic structure through the combination of organic fluorescence emission and another form of emission that is enabled by the surface plasmons in the plasmonic structure. The emission wavelength of the latter depends on the Alq3 thickness and can be tuned within the Alq3 fluorescent spectra. Therefore, a two-color broadband, color-tunable mixed PL structure was obtained. Obvious changes in the Commission Internationale d’Eclairage (CIE) coordinates and the corresponding emission colors of Au-Alq3-Au samples clearly varied with the Alq3 thickness (90, 130, and 156 nm).

Blue organic light-emitting diodes with 2-methyl-9,10-bis(naphthalen-2-yl)anthracene as hole transport and emitting layer and the impedance spectroscopy analysis

2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) based fluorescent blue organic light-emitting diodes (OLEDs) are demonstrated. With MADN as emitting layer, experiments indicate that thick MADN (40–60 nm) is preferable for constructing efficient blue OLED. With MADN as hole-transport and emitting layer and tris(8-hydroxy-quinolinato)aluminium (Alq3) as electron-transport layer, the OLED electroluminescent characteristics show a mixture emission of MADN and Alq3 with Commission Internationale d'Eclairage (CIE) color coordinates of (0.25, 0.34), indicating feasible hole transporting in MADN. Using 4,7-diphenyl-1,10-phenanthroline (BPhen) replacing Alq3 as electron-transport layer, the OLED shows deep blue emission with a maximum luminous efficiency of 4.8 cd/A and CIE color coordinates of (0.16, 0.09). The hole transport characteristics of MADN are further clarified by constructing hole-only device and performing impedance spectroscopy analysis. The results indicate that MADN shows superior hole-transport ability which is almost comparable to typical hole-transport material of N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB), suggesting a promising application for constructing efficient blue OLED with integrated hole-transport layer and emitting layer.

A new zinc–Schiff base complex as an electroluminescent material

A Schiff base bis(salicylidene)propylene-1,3-diamine (salpen)2 and its complex with zinc metal as bis(salicylidene)propylene-1,3-diaminatozinc(II) [Zn(salpen)2] were prepared and characterised by various spectral techniques. The zinc complex had high thermal stability (>300°C) as well as high glass transition temperature (>150°C). Optical properties of the metal complex were studied by UV–visible absorption and photoluminescence emission spectroscopy. Multilayered organic electroluminescent devices were fabricated with a structure ITO/α -NPD/Zinc(salpen)2/BCP/Alq 3/LiF/Al, using the zinc complex as an emissive material. The electroluminescence peak emission was centred at 513 nm with colour chromaticity having Commission Internationale d'Eclairage (CIE) coordinates x=0.26 and y=0.50. A bright blue-green emission with a luminance of 1990 Cd/m2 was recorded at 15 V as an optimum voltage.

Differential inheritance of pepper (Capsicum annuum) fruit pigments results in black to violet fruit colour

AbstractColour is a critical determinant of fruit and vegetable quality. We characterized the inheritance of black and violet immature pepper fruit colour and chlorophyll, carotenoid and anthocyanin pigments responsible for fruit colour. Segregation for black vs. violet fruit colour deviated from expectations for simple inheritance. The primary determinant of fruit colour was the concentration of chlorophyll and carotenoid pigments relative to anthocyanin concentration. Whereas anthocyanin concentration was 34% greater in violet fruit, chlorophyll and carotenoid concentrations were 20‐fold and fourfold greater, respectively, in black fruit relative to concentrations found in violet fruit. Measurement of Commission Internationale d'Eclairage (CIE) colour space scores revealed larger a* values and smaller b* values for violet fruit relative to corresponding parameters for black fruit. An additive–dominance model was sufficient to explain the variation in individual fruit pigments as well as the CIE parameter a*. Addition of additive × additive effects to the additive–dominance model resulted in the best‐fit model m[d][h][i] for L* and b* colour space parameters. For all pigment classes, significant additive effects contributed to the genetic variance for fruit colour.

White luminescence of Ho3+/Tm3+/Yb3+-codoped CaWO4 synthesized via citrate complex route assisted by microwave irradiation

The nanocrystalline Ho3+/Tm3+/Yb3+ co-doped CaWO4 upconversion (UC) phosphors were successfully synthesized by a modified citrate complex method using microwave irradiation. The citrate complex precursors were heat-treated at temperature ranging from 300 to 700 °C for 3 h. Crystallization of the Ho3+/Tm3+/Yb3+ co-doped CaWO4 was detected at 400 °C, and entirely completed at 600 °C. The Ho3+/Tm3+/Yb3+ co-doped CaWO4 heat-treated at 600 °C showed primarily spherical and homogeneous morphology. Under the laser excitation of 980 nm, Ho3+/Tm3+/Yb3+ co-doped CaWO4 shows the bright white upconversion (UC) emission visible to the naked eye, which is composed of a blue emission at 475 nm from Tm3+, and green and red emissions at 543 and 651 nm respectively from Ho3+. The coordinates of Ho3+/Tm3+/Yb3+ co-doped CaWO4 in the Commission International De'eclairage (CIE) chromaticity diagram could be controlled from a cool to a warm white color depending on the Tm3+ and Ho3+ concentrations. The UC luminescent properties on Tm3+ and Ho3+ concentrations and related mechanism based on laser pump power were discussed in detail.

Synthesis of multicolor emitting Sr2−xSmxCeO4 nanophosphor with compositionally tuneable photo and thermoluminescence

Abstract Despite extensive efforts to design a white light generating phosphor, single component phosphors which exhibit multi-color emissions are very limited. In this work we report the synthesis of novel single component colortunable strontium cerate (Sr 2 − x Sm x CeO 4 ) phosphor using facile low temperature solution combustion synthesis. A single-composition, color tunable phosphor is produced by doping with different concentrations of Sm 3+ (0.0 to 0.11) into the Sr 2 CeO 4 matrix. Chromaticity of Sr 2 − x Sm x CeO 4 depends on the Sm 3+ concentration. This is because of energy transfer from Sr 2 CeO 4 to Sm 3+ determines the emission colors of the phosphors. At low concentration of Sm 3+ , Commission Internationale d’Eclairage (CIE) coordinates that are very close to white light emission (0.317, 0.303) are observed. However, at higher dopant concentration ( x = 0.11 of Sm 3+ ) the compound exhibits red emission (0.407, 0.343). Hence, a single host multi-color emitting phosphor is realized by doping and energy transfer. Thermoluminescence studies are carried out for Sr 2 CeO 4 :Sm 3+ phosphor using γ-irradiation in the dose range of 0.5 to 5 kGy. The kinetic parameters, namely activation energy ( E ), frequency factor ( s ) and order of kinetics ( b ) were estimated by Chen’s glow peak shape method and are discussed in detail for their possible usage in dosimetry.

Saturated and Multi‐Colored Electroluminescence from Quantum Dots Based Light Emitting Electrochemical Cells

Novel light emitting electrochemical cells (LECs) are fabricated using CdSe‐CdS (core‐shell) quantum dots (QDs) of tuned size and emission blended with polyvinylcarbazole (PVK) and the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIM‐PF6). The performances of cells constructed using sequential device layers of indium tin oxide (ITO), poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS), the QD/PVK/IL active layer, and Al are evaluated. Only color saturated electroluminescence from the QDs is observed, without any other emissions from the polymer host or the electrolyte. Blue, green, and red QD‐LECs are prepared. The maximum brightness (≈1000 cd m‐2) and current efficiency (1.9 cd A‐1) are comparable to polymer LECs and multilayer QD‐LEDs. White‐light QD‐LECs with Commission Internationale d'Eclairage (CIE) coordinates (0.33, 0.33) are prepared by tuning the mass ratio of R:G:B QDs in the active layer and voltage applied. Transparent QD‐LECs fabricated using transparent silver nanowire (AgNW) composites as the cathode yield an average transmittance greater than 88% over the visible range. Flexible devices are demonstrated by replacing the glass substrates with polyethylene terephthalate (PET).

A tunable lighting system integrated by inorganic and transparent organic light-emitting diodes

A tunable surface-emitting integrated lighting system is constructed using a combination of inorganic light-emitting diodes (LEDs) and transparent organic LEDs (OLEDs). An RB two-color LED is used to supply red and blue light emission, and a green organic LED is used to supply green light emission. Currents of the LED and OLED are tuned to produce a white color, showing different Commission Internationale d’Eclairage (CIE) chromaticity coordinates and correlated color temperatures with a wide adjustable range. Such an integration can compensate for the lack of the LED’s luminance uniformity and the transparent OLED’s luminance intensity.

Effect of Different Chemical Disinfectants on Color Stability of Acrylic Denture Teeth

The purpose of this study was to evaluate the effects of chemical disinfectants on the color stability of acrylic denture teeth (ADT) via spectrophotometric analysis. A total of 120 central ADT specimens were randomly assigned to eight experimental groups and immersed in the following solutions (n = 15). Tap water/control group (CON), neutral soap (NTS), 2% sodium hypochlorite (SHC1), 5.25% sodium hypochlorite (SHC2), sodium perborate (SPB), povidone-iodine (PVI), chlorhexidine gluconate (CHG), and glutaraldehyde (GTA). Color measurements of teeth were performed by spectrophotometry after 10, 30, 48, 72, 144, and 960 immersion cycles in each tested solution. Color differences (ΔE*) were then evaluated using the Commission Internationale D'Eclairage (CIE) L*a* b* color system. Furthermore, Kruskal-Wallis, Mann-Whitney U, and Friedman comparison tests (α = 0.05) were performed on all data. There were significant differences in ΔE* values (p < 0.05) among the eight experimental groups. In addition, the highest ∆E* values were obtained in group SHC2, followed, respectively, by the SHC1, CHG, SPB, PVI, NTS, and CON groups. All the chemical disinfectants used in the study affected the color values of ADTs. Furthermore, ΔE* values increased along with the number of immersion cycles and total immersion time.