The Effect of Recombination Zone Positon on the Color Temperature Performance in the Color-Tunable White Organic Light-Emitting Diode

Using a color-tunable organic light-emitting diode (CT-OLED) can accord with the circadian cycle of humans and realize healthy lighting. The variation range of the correlated color temperature (CCT) is an important parameter to measure the performance of CT-OLEDs. In this paper, the effect of changing the utilization of phosphorescent materials and the position of the recombination zone (RZ) in the device are investigated by changing the thickness of the emissive layer (EML) and the doping ratio of the host and guest materials. The results show that reducing the red phosphorescent material and improving the blue phosphorescent material can affect the change direction of CCT, but it is not enough to expand the span of CCT (ΔCCT). It is more conducive to improving ΔCCT by more reasonable regulation of the position of the main RZ in EML and the energy transfer from the blue sub-EML to the red sub-EML. Device D obtains the best electro-optic and spectral characteristics, in which the maximum ΔCCT is 5746 K (2661 - 8407 K) as the voltage changes from 3.75 V to 9.75 V, the maximum current efficiency and luminance reach 18.34 cd·A-1 and 12,100 cd·m-2, respectively.

The effects of light illuminance and correlated color temperature on mood and creativity

The lighting environment is one of the indoor environmental factors that may influence creativity.The combined effects of illumination(300 lx vs.2000 lx)and color temperature(3000 K vs.6000 K)on mood and creativity were investigated in 24 participants.During exposure,participants completed questionnaires to assess their mood and lighting perceptions,performed creative and analytical tasks,and collected saliva samples for analysis of melatonin concentration.An interactive effect of illuminance and color temperature on the mood was observed.The participants performed better on the performance of Flexibility,Fluency and Originality in the verbal creative task when they expressed higher positive mood(at 2000 lx,6000 K and 300 lx,3000 K)and performed better on the performance of Resistance to closure in the figural creative task when they reported the lowest positive mood(at 2000 lx,3000 K).Analytical thinking,including calculation and echoic memory skills,was facilitated at the lighting setting(300 lx,6000 K)that induced the least affective intensity.No significant difference in melatonin concentration was observed.This evidence implies that the affective state of the occupants was influenced by light and that their creative performance was altered accordingly.These findings will help to elaborate a design guideline on the lighting environment according to the specific needs of different tasks.

Fabrication of High Color Rendering Index White Light Emitting Diodes from Gold Nanoclusters

We demonstrated gold nanoclusters as color tunable emissive light converters for the application of white light emitting diodes (WLEDs). A blue LED providing 460 nm to excite gold nanoclusters mixed with UV curable material generates broad bandwidth emission at the visible range. Increasing the amount of gold nanoclusters, the correlated color temperature of WLEDs tuned from cold white to warm white, and also results in the variation of color rendering index (CRI). The highest CRI in the experiment is 92.

RESEARCH ON COLOR CONSTANCY UNDER OPEN ILLUMINATION CONDITIONS

Color information plays a key role in the research fields of object recognition and image retrieval. However, the actual color varies by the conditions of illumination, especially the open natural daylight. Four different color constancy schemes are proposed in the paper to minimize the effects of open illumination conditions. (1) The color constancy scheme based on the image statistics is proposed, which includes the color cast detection and removal. (2) The color constancy scheme based on the color temperature curve is proposed, which combines Gaussian model with linear fitting to estimate color temperature curve. (3) The color constancy scheme based on the double exposure theory is proposed, which is able to reproduce a color image under typical illumination. (4) According to the concepts of supervised learning, the supervised color constancy scheme is proposed. The transformation of color values from unknown illumination to typical illumination is solved by improved Support Vector Regression (SVR).

Alerting effects of light in healthy individuals: a systematic review and meta-analysis

Light plays an essential role in psychobiological and psychophysiological processes,such as alertness.The alerting effect is influenced by light characteristics and the timing of interventions.This meta-analysis is the first to systematically review the effect of light intervention on alertness and to discuss the optimal protocol for light intervention.In this meta-analysis,registered at PROSPERO(Registration ID:CRD42020181485),we conducted a systematic search of the Web of Science,PubMed,and PsycINFO databases for studies published in English prior to August 2021.The outcomes included both subjective and objective alertness.Subgroup analyses considered a variety of factors,such as wavelength,correlated color temperature(CCT),light illuminance,and timing of interventions(daytime,night-time,or all day).Twenty-seven crossover studies and two parallel-group studies were included in this meta-analysis,with a total of 1210 healthy participants(636(52%)male,mean age 25.62 years).The results revealed that light intervention had a positive effect on both subjective alertness(standardized mean difference(SMD)=-0.28,95%confidence interval(CI):-0.49 to-0.06,P=0.01)and objective alertness in healthy subjects(SMD=-0.34,95%CI:-0.68 to-0.01,P=0.04).The subgroup analysis revealed that cold light was better than warm light in improving subjective alertness(SMD=-0.37,95%CI:-0.65 to-0.10,P=0.007,I2=26%)and objective alertness(SMD=-0.36,95%CI:-0.66 to-0.07,P=0.02,I2=0).Both daytime(SMD=-0.22,95%CI:-0.37 to-0.07,P=0.005,I2=74%)and night-time(SMD=-0.32,95%CI:-0.61 to-0.02,P=0.04,I2=0)light exposure improved subjective alertness.The results of this meta-analysis and systematic review indicate that light exposure is associated with significant improvement in subjective and objective alertness.In addition,light exposure with a higher CCT was more effective in improving alertness than light exposure with a lower CCT.Our results also suggest that both daytime and night-time light exposure can improve subjective alertness.

Influence of Y^(3+),Bi^(3+) Content on Photoluminescence of YVO_4∶Dy^(3+) Phosphor Induced by Ultraviolet Excitation

YxVO4∶0.01Dy3+ and Y0.99-xVO4∶0.01Dy3+,xBi3+ phosphors were synthesized by chemical co-precipitation method.Their crystal structure,micromorphology and photoluminescence(PL) properties were investigated by X-ray diffraction(XRD),scan electron microscopy(SEM) and spectrofluorometer.YxVO4∶0.01Dy3+ and Y0.99-xVO4∶0.01Dy3+,xBi3+ phosphors have a broad excitation band from about 250 to 350 nm including a strongest peak at about 310 nm.Under its excitation,the emission spectra exhibits two sharp peaks,one of which centered at about 483 nm for 4F9/2→6H15/2 transition of Dy3+ and the other at about 574 nm due to the 4F9/2→6H13/2 transition of Dy3+.For YxVO4∶0.01Dy3+(x=0.94,0.97,0.99,1.01,1.03) phosphor,with increasing value of x,the body color of phosphor changes from yellow to white and the strongest peak in the excitation spectra shifts a little to shorter wavelength.It is detrimental to luminous intensity when Y3+ content deviates stoichiometric ratio.For Y0.99-xVO4∶0.01Dy3+,xBi3+(x=0.01,0.05,0.1,0.15,0.2,0.25) phosphor,the samples have extraneous bismuth vanadium oxide phase except for the major tetragonal zircon structure when x≥0.20.With increasing value of x,the band edge in the excitation spectra shifts to longer wavelength,the excitation intensity and luminous intensity increase early and decrease late.When the value of x is 0.01,the intensities increase evidently.In addition,the influence of Y3+ or Bi3+ on the color temperature of emission and micromorphology of YVO4∶Dy3+ is slight.

Synthesis of γ-Ce_2S_3 colorant under low temperature and its coloring properties for PE and PVC

A series of cerium sulfides were successfully prepared using commercially available nanoscale CeO_2 as precursor, anhydrous Na_2CO_3 as dopants, CS_2 as sulfur source, under 600–800 oC, respectively. Properties of samples were investigated by means of X-ray diffraction（XRD）, scanning electron microscopy（SEM） and spectrophotometry. The results showed that corresponding γ-Ce_2S_3 with small size was obtained by using nanoscale CeO_2 as precursor; pure phase γ-Ce_2S_3 could be obtained under low temperature of 700 oC. Coloring properties of γ-Ce_2S_3 obtained under 800 oC were studied by researching γ-Ce_2S_3/PE and γ-Ce_2S_3/PVC composites, respectively. The results showed that satisfied coloring effects to PE and PVC were obtained by using 0.5 phr and 0.2 phr γ-Ce_2S_3, respectively.

Red-emitting YAG:Ce,Mn transparent ceramics for warm WLEDs application

A series of YAG:Ce,Mn transparent ceramics were prepared via a solid-state reaction-vacuum sintering method.The effects of various Mn^2+–Si4+pair doping levels on the structure,transmittance,and luminescence properties were systematically investigated.These transparent ceramics have average grain sizes of 10–16μm,clean grain boundaries,and excellent transmittance up to 83.4%at 800 nm.Under the excitation of 460 nm,three obvious emission peaks appear at 533,590,and 745 nm,which can be assigned to the transition 5 d→4 f of Ce^3+and 4 T1→6 A1 of Mn^2+.Thus,the Mn^2+–Si4+pairs can effectively modulate the emission spectrum by compensating broad orange-red and red spectrum component to yield high quality warm white light.After the optimized YAG:Ce,Mn transparent ceramic packaged with blue light-emitting diode(LED)chips,correlated color temperature(CCT)as low as 3723 K and luminous efficiency(LE)as high as 96.54 lm/W were achieved,implying a very promising candidate for application in white light-emitting diodes(WLEDs)industry.

Luminescent properties of Dy^3+/Eu^3+ doped fluorescent glass for white LED based on oxyfluoride matrix

Rare earth ion-doped fluorescent glass has become a hotspot due to its characteristics.This work shows that the prepared Dy^3+and Dy^3+/Eu^3+doped glasses have white light emission under ultraviolet excitation.There is a higher yellow light/blue light(Y/B)value,indicating an increase in the covalentity of Dy-O,and decrease in the symmetry with the increasing concentration of dopants(Dy^3+).The correlated color temperature(CCT)can be effectively reduced by the red light emission of Eu^3+,and the order of influence of excitation wavelength on CCT is 395 nm>382 nm>365 nm.The delay curve demonstrates the energy transfer from Dy^3+to Eu^3+.The glass has the characteristics of anti-blue light damage and wide tunable color temperature,which illustrates that it has potential application in the field of white LED.

Peak wavelength selection guides of chip and phosphors for phosphor-converted white light-emitting diodes

The dependences of light efficiency of radiation （LER） and color-rendering index （CRI） of trichromatic white light-emitting diode （wLED）, composed of blue LED die, green/yellow, and red phosphors, on the peak wave- length of each primary were investigated by theoretical calculations, at correlative color temperature （CCT） from 2,700 to 6,500 K. The peak wavelength of InGaN based blue LED chip ranges from 450 to 471 nm, while those of Ca3Sc2Si3012：Ce3＋, b-SiA1ON：Eu2＋, and Y3A15012：Ce3＋ based green/yellow phosphors range from 511 to 572 nm, and those of Sr2SisN8：Eu2＋ and CaA1SiN3：Eu2＋ red phosphors range from 620 to 650 nm, which cover almost all the practically used, commercially available wave bands until now. Then, based on the results, selection guides of peak wavelengths for blue LED chip and phosphors to obtain tradeoff LER 〉280 lm.W-1 as well as CRI 〉80 in all CCTs are proposed. The favorable wave bands of each primary are suggested.