Search query: CQD-LEDs with High Colour Rendering Index

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abstract: Quantum dots (QD) which is considered the ideal candidate of third generation semiconductor lighting, has the advantages of high quantum yield, adjustable emission wavelength and narrow full width at half maxima (FWHM) thus it is an ideal choice as the colour converting materials for LEDs. InGaN LEDs are the main choice of solid state lighting, which is always applied with Ce doped yttrium aluminum garnet (YAG: Ce3+ yellow phosphor to achieve white light. However, white light achieved by this method has a low colour rendering index (CRI) mainly because of the missing of red spectral components in YAG: Ce3+ thus the CRI is lower than 80 and the correlated colour temperature (CCT) is always above 6500K. In order to increase the CRI of white LEDs, in this paper, we fabricated yellow CQDs and applied it on blue LED chips, red QD films were also used to increase the CRI of our white LEDs. The result shows that the white LEDs with yellow CQDs and red QD films has a max CRI of 94.3 at a driving current of 70mA, the Commission International de L'Eclairage (CIE) chromaticity coordinates are (0.325, 0.3435) and the CCT is 5832K, which is white light with high CRI and can be used in indoor lighting.
author_names: Yuxian Yan

Doudou Zhang

Luqiao Yin

Jianhua Zhang
title: CQD LEDs with High Colour Rendering Index
venue: 2020 17th China International Forum on Solid State Lighting 2020 International Forum on Wide Bandgap Semiconductors China (SSLChina: IFWS)
year: 2020

abstract: Existing white LEDs use a blue LED chip to stimulate phosphor powder to form white light. The surface coated with a phosphor layer directly affects the colour rendering index, the luminous efficacy and the colour temperature. We have encapsulated a white LED source with chip on board packaging to meet the requirements for a high power, high colour temperature, high colour rendering index LED using stacked phosphor coating. This chip on board white LED light source can achieve a colour rendering index over 95 and a luminous efficacy over 100 lm/W while the colour temperature is 5700 K. This technology can be widely used in commercial lighting applications where high quality light sources are needed.
author_names: Peng Ge

Z Zhou

Jun Zhang

Haiyan Wang
title: Stacked phosphor coating technology for white LEDs with high colour temperature and high colour rendering index
year: 2019

abstract: Designing two step tuning based on substitution of multiple cation lattices and energy transfer successfully achieved versatile colour output for single phase phosphor converted white LEDs in this work. Herein, we chose whitlockite type Ca9LiY0.667(PO4)7 compound as a host which provides multiple cation sites for Eu2+ occupation. Spectral results indicate that the Ca9LiY0.667(PO4)7:Eu2+ phosphor emits a cold white emission due to its multiple emission bands at about 420, 480, and 530 nm, which correspond to emissions from the M(3) M(1)/M(2) and M(5) cation sites as ascertained by the Rietveld refinement method. In order to enhance the red emission of CLYPO:Eu2+ phosphors, they were codoped with Mn2+ Warm white emission in a single phase host based on energy transfer was successfully obtained in the CLYPO:Eu2+,Mn2+ phosphors. The excitation band of the CLYPO:Eu2+,Mn2+ phosphors in the 360 to 450 nm range perfectly coincides with that of commercial LED chips, implying that these phosphors are desirable for white LED applications. White LEDs with a higher color rendering index (Ra 90.2) and a lower correlated color temperature (CCT 3614 K) were achieved by using a single phase CLYPO:0.03Eu2+,0.10Mn2+ phosphor and a 395 nm InGaN LED chip.
author_names: Mingshan Cui

Jindi Wang

Mengmeng Shang

Jin-Hua Li

Qi Wei

Peipei Dang

Ho Seong Jang

Jun Lin
title: Full visible light emission in Eu2+,Mn2+ doped Ca9LiY0.667(PO4)7 phosphors based on multiple crystal lattice substitution and energy transfer for warm white LEDs with high colour rendering
year: 2019

abstract: CdS/Si multi interface nanoheterojunctions (CdS/Si NPA) were fabricated by depositing CdS nanocrystallites (nc CdS) on silicon nanoporous pillar arrays (Si NPA) by chemical bath deposition. White electroluminescence (EL) with a high colour rendering index from a prototypical light emitting diode based on CdS/Si NPA has been reported, which does not need complex colour mixing or conversion techniques. The white EL can be composed into three primary colours, which include blue emissions from the Si NPA, the green emissions from the bandgap emission of nc CdS and red emissions from the defects in the nc CdS. Through the annealing treatment, the chromaticity coordinate and correlated colour temperature can be tuned. This indicates that CdS/Si NPA is a potential candidate in the one chip white LEDs.
author_names: Yiming Li

Yue Li Song

Peng Fei Ji

Feng Qun Zhou
title: White light emission with tuneable colour temperature and high colour rendering index from CdS/Si multi interface nanoheterojunctions.
venue: Nanoscale
year: 2017

abstract: Existing white light LED technology uses a blue light LED chip to stimulate a phosphor powder to form white light. The phosphor layer on the surface directly affects the colour rendering index, luminous efficacy and colour temperature of the LED. We propose a high power, white LED, chip on board package technology to achieve high colour rendering index and high luminous efficacy by optimising the spectral power distribution. The chip on board package light source can achieve a colour rendering index over 90 and a luminous efficacy over 90 lm/W while the power is 45W. It can be widely used in commercial lighting applications.
author_names: Z Zhou

H Wang

Jingwen Zhang

Jie Su

Peng Ge
title: LED chip on board package with high colour rendering index and high luminous efficacy
year: 2018

abstract: Abstract The circadian rhythm is influenced by light and other non visual responses in humans. Recent researches have shown that the visual quantity illuminance is not appropriate for evaluating non visual effects. Metrics such as the circadian stimulus have been developed to address this issue. One of the limitations with circadian metrics is that the determination requires a spectroradiometer instead of the standard illuminance meters. In this article, a simple circadian stimulus calculation model for white light sources is presented. The model is determined with the parameters illuminance, correlated colour temperature CCT and colour rendering index Ra. The accuracy and reliability of the model is high and is based on 7641 spectra with 19 illuminance levels, which are generated using a heuristic optimisation procedure. In addition, the model has been internally validated with the method repeated split data and has an error deviation of 0.058 for CCT 3710 K and 0.045 for CCT 3710 K at 99% confidence interval in the circadian stimulus CS range between 0.2 and 0.5. Since the quantities illuminance, correlated temperature and colour rendering index are common in practice, this model enables non visual planning of illumination installations by lighting designers or lighting design tools. Furthermore, it allows retrospective analysis of past non visual research results in scientific studies, where illuminance and correlated colour temperature were provided.
author_names: William Truong

Babak Zandi

Vinh Quang Trinh

Tran Quoc Khanh
title: Circadian metric Computation of circadian stimulus using illuminance, correlated colour temperature and colour rendering index
venue: Building and Environment
year: 2020

abstract: This paper describes how CIE colour fidelity index Rf values are correlated with CIE Ra colour rendering index values for typical FL fluorescent lamps. The results shows that for broad band FL lamps Rf doesn't introduce drastically changes in relation to Ra values. The other situation is with narrow band FL lamps whose spectral power distribution was designed for achieving of high Ra value. At that case there is no correlation between Ra and Rf. Streszczenie. W artykule przedstawiono badania nad zaleznoscia wskaznika wiernosci barwy CIE Rf od wskaznika oddawania barw CIE Ra dla standardowych lamp fluorescencyjnych (swietlowek) FL. Wyniki pokazuja, ze dla szerokopasmowych swietlowek, wskaznik Rf nie wprowadza drastycznych zmian w stosunku do wartosci Ra. W przypadku waskopasmowych lamp FL, tj. takich ktorych rozklad widmowy zostal zaprojektowany w celu osiagniecia wysokiej wartosci Ra pomimo faktu iz wizualnie ich swiatlo nie oddaje perfekcyjnie barw, wartosc wskaznika Rf nie koreluje z Ra. (Jakosc oddawania barw wspolczesnych lamp fluorescencyjnych okreslona zdefiniowanym przez CIE wskaznikiem wiernosci barwy oraz wskaznikiem oddawania barw)
author_names: J Kowalska
title: Colour rendition quality of typical fluorescent lamps determined by CIE Colour Fidelity Index and Colour Rendering Index
venue: PRZEGLAD ELEKTROTECHNICZNY
year: 2019

abstract: Lu modified (Ca2.94 xLuxCe0.06)(Sc2 yMgy)Si3O12 (CLSMS Ce3+ yellow emitting phosphors are prepared by a solid state reaction. Controllable luminescent intensity and emitting colour are studied as a function of Lu and Mg contents. Fixing the Mg content to be 1, the effect of Lu content on crystal phase formation, luminescence properties and temperature characteristics is studied. It is revealed that the Lu induced luminescent enhancement is the result of an increase in absorbance of Ce3+ rather than the internal quantum efficiency. Intense and broadband emission is realized by controlling the Lu content to obtain a pure CLSMS crystal phase. The maximum luminescence intensity is obtained at x 0.54, which is as high as 156% of the Lu free phosphor. The Lu containing phosphor also exhibits better temperature characteristics for its big activation energy (0.20 eV) than the Lu free one (0.18 eV) Combining the present phosphor with a blue light emitting diode (LED) chip, a white LED with an excellent colour rendering index Ra of 86 and a high luminous efficiency of 86 lm W 1 is obtained. The results of the present study demonstrate that the CLSMS Ce3+ phosphors show a good performance and are attractive candidates for commercial applications when used in white LEDs.
author_names: Yongfu Liu

Xia Zhang

Zhendong Hao

Wei Lu

Xingyuan Liu

Xiaojun Wang

Jiahua Zhang
title: Crystal structure and luminescence properties of (Ca2.94 xLuxCe0.06)(Sc2 yMgy)Si3O12 phosphors for white LEDs with excellent colour rendering and high luminous efficiency
year: 2011

abstract: Ca8.78Ce (PO4)7:0.06Eu2+,0.16Mn2+,xH3BO3 phosphors were synthesized by a high temperature solid state reaction method. XRD patterns of the samples indicate that H3BO3 doping does not change the phase formation. However, H3BO3 doping can change the emission intensities of Ce3+ Eu2+ Mn2+ and the energy transfer efficiencies of Ce3+ Eu2+ and Ce3+ Mn2+ The reason for this is that H3BO3 doping changes the luminescent centre and the distance between different luminescent centres to some degree. When the ligand polyhedron volume decreases, the lifetime and emission intensity of the luminescent centre will increase. When the distance between Ce3+ and Eu2+/Mn2+ decreases, the energy transfer efficiency between them will increase. In Ca8.78Ce(PO4)7:0.06Eu2+,0.16Mn2+,xH3BO3, the average volume of an (Eu/Mn)1/2/3 O8/9] polyhedron will decrease from 27.511 A3 to 21.847 A3, and the average distance between Ce and (Eu/Mn)1/2 will decrease from 3.702 A to 3.573 A with increased doping amounts of H3BO3 from 0 to 7. Meanwhile, the emission intensity and lifetime of Ce3+ decrease, and those of Eu2+/Mn2+ increase. Furthermore, the energy transfer efficiency from Ce3+ to Eu2+/Mn2+ and the quantum efficiency are improved. H3BO3 doping improves the ratio of red, green and blue colours of the spectrum, which improves the colour rendering index of materials from 80.5 to 90.7. H3BO3 doping also improves the thermal stability of the material to some degree. The quenching temperature of Eu2+ is improved from 75 degC to 100 degC.
author_names: Chao Wang

Zhijun Wang

Jinge Cheng

Zhenling Li

Miaomiao Tian

Zhi-ping Yang

Panlai Li
title: Improvement of emission intensity, colour rendering index and thermal stability of Ca9Ce(PO4)7:Eu2+,Mn2+via H3BO3 doping
year: 2018

abstract: Four heteroleptic platinum complexes (FPtXND) bearing 4 hydroxy 1,5 naphthyridine derivatives functionalized with dimethyl (X mm) phenoxy (X OPh) piperidine (X pp) or carbazole (X Cz) units as one ligand (XND) and 2 (2,4 difluorophenyl)pyridine as the other common ligand (F) were newly synthesized and characterized. The crystal structures of FPtOPhND and FPtCzND were determined by single crystal X ray diffraction crystallography. Although they have a short plane to plane packing distance of 3.62 and 3.39 A, respectively, both platinum complexes have different molecular packing patterns, which affect their photoluminescence (PL) in solution and electroluminescence (EL) in the solid state. Due to the contribution from both monomers and excimers/aggregates, all of the platinum complexes exhibited broad and red shifted PL in concentrated solutions as well as in doped thin films. In the monochromatic organic lighting diode (OLED) testing, FPtXND doped in 4,4' di(9H carbazol 9 yl) 1,1' biphenyl (CBP) exhibited greenish yellow or orange yellow EL, of which FPtOPhND has the highest EL efficiency mainly due to its high solution PL quantum yield of 21% Hybrid white OLEDs were first achieved with a single emitting layer configuration, of which highly fluorescent blue N,N' di 1 naphthalenyl N,N' diphenyl [1,1':4',1':4',1' quaterphenyl] 4,4' diamine (4P NPD) was used as the host material for all four platinum complexes. To improve the performance of the FPtOPhND based hybrid white OLEDs, double emitting layer configurations were adopted with CBP and 4P NPD as the host material. Virtually voltage independent, a white EL having CIEx,y (0.33, 0.31) and a CRI as high as 91 was obtained. The maximum EL efficiency of 11.8% 25.9 cd A 1, or 11.6 lm W 1 was acquired with FPtOPhND doped in the double emitting layer configuration of an OLED.
author_names: Anurach Poloek

Chiao-Wen Lin

Chin-Ti Chen

Chao-Tsen Chen
title: High colour rendering index and colour stable hybrid white efficient OLEDs with a double emitting layer structure using a single phosphorescence dopant of heteroleptic platinum complexes
year: 2014