Chromaticity Coordinate Values Research Articles

Synthesis, crystal structure, and luminescence properties of a novel green emitting phosphor Na2Mg1-xSiO4:Mnx2+

In this paper, a novel green phosphor Na2Mg1-xSiO4:xMn2+ (x = 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.15, 0.20) was successfully synthesized by a traditional solid-state reaction method at 950 °C. The powder X-ray diffraction (PXRD), the photoluminescence excitation and emission spectra (PL and PLE) were measured to systematically study the as-prepared phosphors. The as-obtained Na2MgSiO4:Mn2+ phosphor shows an intense asymmetric green emission spectra with the broad-band peak at 520 nm due to 4T1(4G) → 6A1(6S) transition of the Mn2+ ion. The optimum Mn2+ concentration in this phosphor was 8 mol%. The MnMn critical distance was calculated to be 13.42 Å. The dipole–dipole interaction dominates in the non-radiative energy transfer between the Mn2+ ions and causes the concentration quenching. The decay curve of the Na2MgSiO4:Mn2+ phosphors were discussed. The CIE chromaticity coordinate values (x = 0.163, y = 0.631) of Na2MgSiO4:0.08Mn2+ phosphor were located in green region and the correlated color temperature was 8643 K. The above results indicate that Na2MgSiO4: Mn2+ as a green component can be a good candidate for near UV-excited w-LEDs.

Dual color emitting Eu doped strontium orthosilicate phosphors synthesized by bio-template assisted ultrasound for solid state lightning and display applications

A novel Sr2SiO4:Eu (1–5mol %) superstructures (SS) were synthesized using bio-sacrificial A.V. gel assisted ultrasound method. Powder X-ray diffraction patterns confirmed the presence of both α and β phase formation. It was evident that the morphological growth was highly reliant on A.V. gel concentration, sonication time, pH and sonication power. The formation mechanisms for different hierarchical SS were proposed. From diffuse reflectance spectra, the energy band gap was estimated and found to be ∼4.70–5.11eV. The photoluminescence emission spectra for the excitation at 392nm, shows characteristic emission peaks at 593, 613, 654 and 702nm which were attributed to 5D0→7F0, 7F1,7F2 and 7F3 transitions of Eu3+ ions respectively. Conversely, when the samples were subjected to the heat treatment at 850°C for 3h under argon atmosphere, display an intense broad emission peak with two de-convoluted peaks at 490 and 550nm due to 4f65d1→4f1 (8S7/2) transitions of Eu2+ ions. The concentration quenching phenomenon was discussed which attributes to energy transfer, electron–phonon coupling and ion–ion interaction. The Judd–Ofelt intensity parameters and other radiative properties were estimated by using emission spectra. The CIE chromaticity coordinate values of Sr2SiO4:Eu2+ and Eu3+ nanophosphors were located in green and red regions respectively. The calculated CCT and CRI values specify that the present phosphor can be fairly useful for both green and red components of white LED’s. Luminescence decay and quantum yield suggest the suitability of this phosphor as an efficient luminescent medium for light emitting diodes. Overall, the results elucidated a rapid, environmentally benign, cost-effective and convenient method for Sr2SiO4:Eu3+ synthesis and for the possible applications such as solid state lighting and display devices.

Evaluation of chromaticity coordinates shift for image displayed on liquid crystal panels with various properties on color reproduction

Subject of Research.We consider the problem of evaluation of chromaticity coordinates shift for image displayed on liquid crystal panels with various properties on color reproduction. A mathematical model represents the color reproduction characteristics. The spread of the color characteristics of the screens has a statistical nature. Differences of color reproduction for screens are perceived by the observer in the form of different colors and shades that are displayed on the same type of commercially available screens. Color differences are characterized by numerical measure of the difference of colors and can be mathematically compensated. The solution of accounting problem of the statistical nature of the color characteristics spread for the screens has a particular relevance to aviation instrumentation. Method. Evaluation of chromaticity coordinates shift of the image is based on the application of the Grassmann laws of color mixing.Basic data for quantitative calculation of shift are the profiles of two different liquid crystal panels defined by matrixes of scales for components of primary colors (red, green, blue). The calculation is based on solving the system of equations and calculating the color difference in the XY-plane. In general, the calculation can be performed in other color spaces: UV, Lab. The statistical nature of the spread of the color characteristics for the screens is accounted for in the proposed mathematical model based on the interval setting of coordinate values of the color gamut triangle vertices on the set of commercially available samples. Main Results. Carried outresearches result in the mathematical expressions allowing to recalculate values of chromaticity coordinates of the image displayed on various samples of liquid crystal screens. It is shown that the spread of the color characteristics of the screens follows bivariate normal distribution law with the accuracy sufficient for practice. The results of simulation are given. We present the ellipses of section for histograms of distribution of chromaticity coordinates for five randomly defined colors that are consistent with the theoretical expressions. Practical Relevance. Research results are usable for engineers designing modern indication equipment based on LCD-panels and for manufacturers while colorimetric calculations and estimation of technological tolerance of chromaticity coordinates among display units in mass production as well.

Luminescence properties of a novel green emitting Ba2CaZn2Si6O17:Eu2+ phosphor for white light – Emitting diodes applications

A novel green emitting Ba2CaZn2Si6O17:Eu2+ (BCZSO:Eu2+) phosphor was synthesized using conventional high temperature solid state reaction method. Powder X-ray diffraction was carried out to confirm the phase formation of the synthesized phosphors. Photoluminescence emission spectrum was recorded under excitation at 340 nm. The BCZSO:Eu2+ phosphor exhibited an intense asymmetric green emission band around 502 nm which originated from the 4f65d1 → 4f7 transition of Eu2+ ion. The optimum doping concentration of Eu2+ was found to be 0.06 mol. The energy transfer mechanism among Eu2+ in BCZSO phosphor was found to be a dipole–dipole interaction, and the critical distance (RC) for the Eu2+ ions calculated by the concentration quenching and spectral overlap methods were 23.2 Å and 13.7 Å, respectively. The decay curve of BCZSO:Eu2+ phosphors were discussed. The CIE chromaticity coordinate values (x = 0.259, y = 0.463) of BCZSO:Eu2+ phosphor were located in green region and the correlated color temperature was 7571 K. All these properties gave an indication that BCZSO:Eu2+ phosphor could be a potential green-emitting phosphor for UV based white light emitting diodes.

Алгоритм и методика автоматизации процедуры оценивания координат цветности элементов изображения бортовых средств индикации в авионике

The authors discuss the design of modern on-board equipment for visualization of the air navigation parameters and geo-details (digital district map) with certain requirements to the quality of the visualized information to be displayed. This kind of quality may be characterized in terms of brightness contrast for each color displayed on the screen. In order to ensure stable readability of the image for a pilot, a special procedure should choose chromaticity the coordinates of the image elements. The problem is considered of the research of the avionics on-board indication equipment in order to determine the set of chromaticity coordinate values for the displayed image with the use of automated design tools, which would allow an enhanced visual perception of the image details in the presence of intense external illumination. Various color coding systems used in the on-board indication equipment based on liquid crystal panels (systems of RGB and XY formats) are examined. The calculation of the chromaticity coordinates was based on Maxwell's color mixing triangle by mutual transformations between the elements of XY-plane and decimal codes of RGB-palette, used in the software of the on-board indication equipment. The scheme workstation for the research is proposed, the main components of the developed automated design tools, installed as part of the workstation, are described. The experimental results containing the measures of the brightness levels and estimated brightness contrast values, which were obtained for the given set of colors, are presented. An algorithm for an automated search for a global maximum on the function of two variables, which represents brightness contrast distribution in the chromaticity coordinates plane, is proposed. The decision-making rule approving the use of RGB-codes is the case when the brightness contrast of the test image displayed in any predefined color exceeds two. The results of the research are the methodology and the algorithm of searching the chromaticity coordinate values, which ensure the maximal brightness contrast level and the corresponding values of chromaticity coordinates at the points of maximal contrast.

ANALÝZA BARVY DŘEVA A JEJÍ ZMĚNY VLIVEM SIMULOVANÉHO SLUNEČNÍHO ZÁŘENÍ U TROPICKÝCH DŘEV

This study investigated the wood surface discolouration due to simulated sunlight of three tropical woods native in South America. These woods are commonly used in the Czech Republic. Wood of jatoba (Hymenea courbaril L.), massaranduba (Manilkara bidentata A. Chev.) and tigerwood (Astronium graveolens Jacq.) was exposed to treatment by light of xenon-arc lamp, which simulates outdoor sunlight, for 144 hours. Colour measurements of exposed and non-exposed areas of samples were performed by means of spectrophotometer measuring in CIEL*a*b* colour system. The resulting wood discolouration was evaluated according to value of the overall colour change ∆E*. Changes of particular parameters (L*, a* and b*) were also observed during exposure. The wood surface darkened rapidly during the first hours of exposure to simulated sunlight, then samples showed only a slight increase in lightness. After 144 hours of sunlight irradiation the values of chromaticity coordinates were lower compared with the original surface. The initial variations in the lightness of different wood decreased to the minimum after exposure. The most distinctive discolouration of wood was found in the initially brightest wood tigerwood, the darkest massaranduba was affected the least.

Optical properties and carrier dynamics of CaSrSiO4:Eu3+ phosphors prepared by using the solid-state reaction method

The optical properties and the carrier dynamics of CaSrSiO4:Eu3+ phosphors synthesized by using a solid-state reaction method have been studied by means of scanning electron microscopy, X-ray diffraction, photoluminescence (PL), PL excitation, time-resolved PL, and PL quantum-yield measurements. The phosphor synthesized with a Eu concentration of 5% and sintered at 1380 °C for 2 h in air showed a high quantum yield of 88.53% and good CIE chromaticity coordinate values. The strong excitation bands observed at 395 nm (7F0-5L6) and 466 nm (7F0-5D2) lead to an intense 5D0-7F2 transition (614 nm). The forbidden transitions (5D0-7F0 and 5D0-7F2) were observed and showed lifetimes shorter than that of the magnetic dipole transition (5D0-7F1).

Synthesis and luminescent properties of high brightness MRE(MoO4)2:Eu3+ (M = Li, Na, K; RE = Gd, Y, Lu) red phosphors for white LEDs

A series of Eu3+-activated double molybdate phosphors MRE(MoO4)2 (M = Li, Na, K; RE = Gd, Y, Lu) have been successfully prepared via the conventional solid-state reaction method. The effects of alkali cations and rare earth ions on the luminescence of MRE(MoO4)2:Eu3+ were investigated in detail. The experimental results show that the emission intensity was found to decrease with increasing the size of alkali cations or decreasing the size of rare earth ions. Under 393 nm light excitation, all compounds exhibited strong red emission at about 613 nm due to 5D0 → 7F2 transition of Eu3+. Compared with the commercially available red phosphor Y2O3:Eu3+, the emission intensity of the obtained phosphors is much stronger than that of Y2O3:Eu3+. Additionally, the excitation spectra of these phosphors implied that the MRE(MoO4)2:Eu3+ phosphors can absorb not only the emission of near UV-LED chips but also that of blue LED chips. The CIE chromaticity coordinates are close to the National Television Standard Committee (NTSC) standard CIE chromaticity coordinate values for red (0.67, 0.33). All the results indicate that these phosphors are promising red-emitting phosphors pumped by near-UV or blue light.

Development of Dy3+ activated K2MgP2O7 pyrophosphate phosphor for energy saving lamp

Present work reports, synthesis of Dy3+ activated K2MgP2O7 pyrophosphate phosphor by using modified solid state diffusion that has been studied for its X-ray diffraction pattern (XRD). Furthermore, the chromaticity coordinate values were estimated from emission spectra of K2MgP2O7. The photoluminescence emission spectra of the phosphors having an excitation at around 351nm (mercury free) showed two distinguishing bands centered at around 485nm (blue) and 575nm (yellow) corresponding to 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+, respectively. These phosphors have strong absorption in the near UV region. K2MgP2O7 pyrophosphate phosphor is suitable for color converter using UV light as the primary light source, which can be used as a blue/yellow phosphor excited by n-UV LED chip and mixed with other color emission phosphors to obtain white light. The 300–400nm is Hg-free excitation (mercury excitation is 85% 254nm wavelength of light and 15% other wavelengths), which is characteristic of solid-state lighting phosphors. Hence PL emission in trivalent dysprosium may be efficient photoluminescent materials for solid-state lighting phosphors. The intact study reveals that the present phosphor have promising applications in the lamp industry especially for solid state lighting (mercury-free excited lamp phosphor) and white light LED.

Intensive green emission of ZnAl_2O_4:Mn^2+under vacuum ultraviolet and low-voltage cathode ray excitation

A series of Zn(1-x)Mn(x)Al(2)O(4) (x=0.001∼0.08) phosphors were synthesized by a traditional solid-state reaction route. Their photoluminescence under vacuum ultraviolet (VUV, energy E>50000 cm(-1), wavelength λ<200 nm) and cathodoluminescence under low-voltage electron beam excitation were evaluated. The luminescence decays were also measured. The intense green emission was observed with a peak at about 510 nm upon 172/147 nm excitation. The luminescence of optimum phosphor Zn(0.99)Mn(0.01)Al(2)O(4) (ZAM) was compared with that of commercial green phosphor Zn(2)SiO(4):Mn(2+) (ZSM). The maximum emission intensity of ZAM is larger than that of ZSM under 172/147 nm and low-voltage electron beam excitation. The values of chromaticity coordinates reveal the phosphors can evidently enlarge the tricolor gamut. The results show that the ZnAl(2)O(4):Mn(2+) phosphors may be considered as candidates for Hg-free lamps, plasma flat backlights, and field emission backlights for liquid crystal displays.

Luminescence in Eu 2+ -activated microcrystalline pyrophosphor

A microcrystalline Sr2P207:Eu2+ pyrophosphate-based phosphor was prepared by the modified solid-state diffusion. The crystalline phases were recognised using X-ray diffraction and surface morphology was studied by scanning electron microscope. Photoluminescence properties were investigated under ultraviolet-ray excitation. The Sr2P207:Eu2+ exhibits unique colour: a blue band centred at 430 nm originating from Eu2+ when excited at 328 nm, Commission Internationale de l&apos;Eclairage chromaticity coordinate values are calculated from emission spectra of Sr2P207:Eu2+ for the prepared sample. The results show Sr2P207 is a promising microcrystalline host lattice for the solid-state lighting.

Synthesis and Properties of Aggregation-Induced Emission Compounds Containing Triphenylethene and Tetraphenylethene Moieties

Aggregation-induced emission compounds containing triphenylethene and tetraphenylethene moieties with high thermal stability and good device properties have been synthesized. Their maximum fluorescence emission wavelengths are 469–493 nm in solid states. The glass transition temperatures range from 138 to 180 °C and the decomposition temperatures are 495–557 °C. The unoptimized device fabricated with the triphenylethene compound combined with three tetraphenylethene groups as emitters turns on at ∼6 V and the maximum luminance is observed at ∼1908 cd/m2 and 15.5 V. The electroluminescence peak of the device is at 474 nm and the Commission Internationale de l’Eclairage (CIE) chromaticity coordinate values are (0.18, 0.31) at 10 V.

Simulation of Temperature Induced Colorimetric Shift of YAG:Ce&lt;sub&gt;0.06&lt;/sub&gt;,GD&lt;sub&gt;x&lt;/sub&gt; Phosphor

YAG:Ce0.06,Gdx phosphors were prepared by solid-state method, and temperature dependence of chromaticity coordinate and correlated color temperature of YAG:Ce0.06,Gdx are investigated. Three PL spectra all have broad emission band between 500 nm and 620 nm is assigned to the combination of the lowest energy of 5d bands and the 2F5/2 and 2F7/2 states respectively. With increasing temperature, the x values of chromaticity coordinates of YAG:Ce0.06,Gdx with Gd concentration increase all increase, but y values all decrease. Differently, z values do not show a clear trend. Moreover, correlated color temperature of YAG:Ce0.06,Gdx with Gd concentration increase all decrease with the temperature increase.

Red Emission of Ca[sub 6]Gd[sub 1.97]Eu[sub 0.03]Na[sub 2](PO[sub 4])[sub 6]F[sub 2] with Suitable Chromaticity Coordinates under VUV Excitation

Europium-activated apatite phosphors Ca 6 Gd 2-x Eu x Na 2 (PO 4 ) 6 F 2 (x = 0.01, 0.03, 0.05, 0.07, 0.09, and 0.10) were prepared by a conventional solid-state reaction method. The vacuum ultraviolet (VUV)-vis spectroscopic properties were investigated. The luminescence of optimum phosphor Ca 6 Gd 1.97 Eu 0.03 Na 2 (PO 4 ) 6 F 2 (CGPF-Eu) is compared with that of commercially available red phosphor (Y,Gd)BO 3 :Eu (YGB-Eu). The result shows that the luminescence intensity of CGPF-Eu is around 70.6% of that of YGB-Eu upon 172 nm excitation. The values of chromaticity coordinates and the luminescence photographs demonstrate that CGPF-Eu has a more suitable red emission than YGB-Eu.

SrS:Ce/ZnS:Mn-A di-band phosphor for near-UV and blue LED-converted white-light emitting diodes

The SrS:Ce/ZnS:Mn phosphor blends with various combination viz 75:25, 50:50 and 25:75 were assign to generate the white-light emission using near-UV and blue-light emitting diodes (LED) as an excitation source. The SrS:Ce exhibits strong absorption at 427 nm and the corresponding intense emission occurs at 480 and 540 nm due to electron transition from 5d( 2D)−4f( 2F 5/2, 7/2) of Ce 3+ ion as a result of spin–orbit coupling. The ZnS:Mn excited under same wavelength shows broad emission band with λ max=582 nm originates due to 3d ( 4G− 6S) level of Mn 2+. Photoluminescence studies of phosphor blend excited using near-UV to blue light confirms the emitted radiation varies from cool to warm white light in the range 430–600 nm, applicable to LED lightings. The CIE chromaticity coordinate values measured using SrS:Ce/ZnS:Mn phosphor blend-coated 430 nm LED pumped phosphors in the ratio 75:25, 50:50 and 25:75 are found to be (0.235, 0.125), (0.280, 0.190) and (0.285, 0.250), respectively.

Color tuning of Y 3Al 5O 12:Ce phosphor and their blend for white LEDs

Gadolinium or lanthanum co-doped (0.5 mole) yttrium aluminum garnet doped with cerium phosphors were synthesized by a citric acid gel method and the effect of co-dopants on the structural and luminescent properties were studied. A significant peak shift in the photoluminescence spectra of yttrium aluminum garnet doped cerium was observed from 535 to 556 and 576 nm for gadolinium or lanthanum co-doped phosphors, respectively. The color tuned phosphor were blended with yttrium aluminum garnet doped cerium which showed a considerable improvement in the Commission International De Eclairage chromaticity co-ordinate values of gallium nitride based blue light emitting diode pumped white light. White light emitted from yttrium aluminum garnet doped cerium shows a Commission International De Eclairage value of (0.229, 0.182) whereas the yttrium aluminum garnet doped cerium phosphor blended with gadolinium or lanthanum co-doped phosphor shows (0.262, 0.243) and (0.295, 0.282), respectively. These results demonstrate the possibility to use these phosphor blends to enhance the white light generation in the field of white-light emitting diode solid-state lighting.

Cerium-based phosphors: blue luminescent properties for applications in optical displays

In this paper, we describe the blue photoluminescence (PL) observed in the multi-component oxosalt phosphor GdVO4:Ce3+. Different doping concentrations (0.25–1 mol%) and heat treatment (900–1100 °C) were used to evaluate which conditions would lead to the most suitable blue phosphor for optimal display performance. The cerium doping concentration influences the profile of the emission spectrum (broad peak at 412 nm under UV excitation at 330 nm), as reflected on the values of chromaticity coordinates. On the basis of luminescent properties, we can conclude that, among the phosphors prepared in this work the most adequate for a blue display is the one obtained via the combustion method using glycine as fuel, a 0.50 mol% cerium doping concentration, and heat treatment at 1000 °C.

Radiation-induced changes in some SSNTDs

A comparative study of the effect of fast neutrons and alpha particles on the color changes of some solid state nuclear track detectors was performed. Samples from CR-39 diglycol carbonate and Makrofol polycarbonate were classified into two main groups. The first group was exposed to neutrons of energies in the range between 4.4 and 19.2 MeV, while the second group was irradiated with alpha particles of initial energies in the range between 5.1 and 34 MeV. The transmission of these samples in the wavelength range 200–2000 nm, as well as any color changes, was studied. A characteristic transmission band with different intensities in the wavelength range 200–2000 nm was observed when the samples were exposed to alpha particles, while the interaction of fast neutrons on these detectors, CR-39, may lead to the appearance of new transmission bands at some particular wavelengths. Using the transmission data, both the tristimulus and chromaticity coordinate values were calculated. In addition, the color differences between the non-irradiated sample and those irradiated with different neutron or alpha doses were calculated. The results indicate that both CR-39 and Makrofol detectors acquire color changes under fast neutrons or alpha particles irradiation, but the Makrofol detector has more response to color change than CR-39.

Two methods for the analysis of colorimetric components applied to plant stress monitoring

Abstract Several authors have shown the possibility of early detection of many stress conditions in plants by analysing leaf colour. The availability of portable instruments, increasingly accurate and reliable, leads to the belief that, in the near future, this technique could be used for routine analysis in the field. Nevertheless, due to the variability of the leaf colour parameter and consequently to the large amount of data to be collected to obtain a representative sample, direct analysis of chromaticity coordinate values, as generated by an instrument, could give results that are hard to interpret, especially when the colour variation to be detected is subtle, such as in leaves at the first stages of stress. The availability of standard methodologies to analyse colorimetric data would allow them to be interpreted correctly and, in a short time, to widen their fields of application. In this work two methods of elaboration, with related software (PCA and COLORE) that give an objective evaluation of colorimetric variations of stressed plants by means of specific indexes of alteration, are illustrated. PCA, based on principal components analysis, allows two `indexes', Tij and D, to be calculated, that can describe the differences between two or more treatments. It also allows the location of the different treatments on the chromaticity diagram to be graphically represented. COLORE calculates the values of the dominant wavelength and purity of the colour. From these, it computes the CI index that can be related to degree of stress. The two softwares were applied to data from different studies of thermal and water stress in Sorghum bicolor ((L.) Moench) and Citrus macrophylla (L). The results showed a clear correlation between the colorimetric indexes and the ecophysiological parameters chosen as indicators of stress.

The effect of UV radiation on the optical properties of cellulose triacetate

The effect of UV light irradiation on the optical properties of cellulose triacetate (CTA) were investigated. Refractive index measurements were studied using both solution and solid state samples of the polymer. These samples were exposed for different exposure times, in the range 10 min to 10 h, at levels between 2.3 and 113 kJ/cm 2). The absorbance of the CTA samples in the ultraviolet range, as well as any colour changes, were also studied. Using the transmission data, both the tristimulus and chromaticity coordinate values were calculated. The refractive index measurements exhibited the same trends for both the solid and the solution samples. Such behaviour indicated that above 60 min (11.3 kJ/cm 2) the UV light irradiation enhances the isotropic character of the polymer.