White light-emitting diodes using thermally and photochemically stable fluorescent silica nanoparticles as color-converters

Article abstract of DOI:10.1039/c3tc30967c

Trialkoxysilyl terminal groups were directly introduced into fluorescent organic dye molecules by consecutive allylation and hydrosilation reactions; the derivatized dye molecules were then successfully embedded into silica nanoparticles by the Stoeber method. Those fluorescent silica nanoparticles (FSNPs) had emission colors corresponding to each fluorescent organic dye used (yellowish-green and red) and showed excellent thermal and photochemical stabilities. A white light-emitting diode (WLED) was fabricated by combining the FSNP/silicone encapsulant composite incorporated with FSNPs having yellowish-green and red emission with a blue InGaN LED (BLED). The resulting three-color RGB FSNP-LED exhibited a good color rendering index (CRI), Ra 86.7, at the correlated color temperature of 5452.6 K and CIE coordinates of (0.3334, 0.3360), indicating that the combination of highly fluorescent silica nanoparticles with LEDs can offer a promising solution for white light sources with high color rendering properties.

Full text of DOI:10.1039/c3tc30967c

Journal of
Materials Chemistry C
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PAPER
White light-emitting diodes using thermally and
photochemically stable fluorescent silica nanoparticles
as color-converters†
Cite this: J. Mater. Chem. C, 2013, 1,
5879
*
Hak-Sung Jung, Young-Jae Kim, Shin-Woo Ha and Jin-Kyu Lee
Trialkoxysilylterminalgroups were directly introduced intofluorescent organicdyemoleculesby consecutive
allylation and hydrosilation reactions; the derivatized dye molecules were then successfully embedded into
¨
silica nanoparticles by the Stober method. Those fluorescent silica nanoparticles (FSNPs) had emission colors
corresponding to each fluorescent organic dye used (yellowish-green and red) and showed excellent
thermal and photochemical stabilities. A white light-emitting diode (WLED) was fabricated by combining
the FSNP/silicone encapsulant composite incorporated with FSNPs having yellowish-green and red
emission with a blue InGaN LED (BLED). The resulting three-color RGB FSNP-LED exhibited a good color
rendering index (CRI), Ra 86.7, at the correlated color temperature of 5452.6 K and CIE coordinates of
(0.3334, 0.3360), indicating that the combination of highly fluorescent silica nanoparticles with LEDs can
offer a promising solution for white light sources with high color rendering properties.
Received 23rd May 2013
Accepted 23rd July 2013
DOI: 10.1039/c3tc30967c
www.rsc.org/MaterialsC
stability, which is attributed to the high melting point, high
hardness, and stable thermal and chemical properties.9,10
Introduction
Approximately 20% of global energy consumption is used for
the production of light.1 Increasing energy demands along with
mounting concerns of global warming and climate change have
placed an enormous emphasis on the exploration of high-effi-
ciency light sources to reduce energy consumption.2–4 Solid-
state lighting devices such as light-emitting diodes (LEDs) are
the most promising alternative, because they provide high
luminescence efficiencies, quick response times, long lifetimes
and high mechanical stabilities.5,6 Currently, white LEDs
(WLEDs) have attracted a great deal of attention as their
commercialization continues to expand to high-volume appli-
cations, including general lighting and liquid crystal displays
(LCDs) of digital cameras, cellular phones, and monitors of
notebook computers.7,8
Although red, green, and blue emissions are commonly
mixed together to generate white light, this can also be achieved
by simply adding blue to yellow light. In recent years, the most
popular commercial WLEDs are based on a blue InGaN LED
chip with a yellow-emitting phosphor of cerium-doped yttrium
aluminum garnet (YAG:Ce3+). The ubiquity of YAG:Ce3+ phos-
phors in commercial devices is attributed to their simpler and
more cost-effective fabrication as well as their long term
However, YAG:Ce-based WLEDs have a low color rendering
index (CRI) because of their lack of color in the red region. In an
attempt to improve color rendering properties, green-emitting
SrGa2S4:Eu2+ or green-emitting a-sialon:Yb2+ phosphors have
been mixed with red-emitting Ca1ꢀxSrxS:Eu2+ or red-emitting
Sr2Si5N8:Eu2+ phosphors respectively.11,12 Unfortunately, sulde
phosphors are thermally and chemically unstable and tend to
reach luminescence saturation with increasing applied current
when incorporated into WLEDs.11,13 With respect to nitride
phosphors, extreme preparation conditions, including high
temperature and high nitrogen pressures, are required.12,14,15
Moreover, the phosphors commonly exhibit uorescence reab-
sorption and non-uniformity of luminescent properties,
resulting in the loss of luminous efficiency and time-dependent
shi of color point.16
With this background in mind, organic luminescence
converters are attractive alternatives because of their broad
absorption and emission, moderate price, and ease of fabrica-
tion. There have been attempts to use organic luminescence
converters for LED applications,17–19 but there are concerns over
their stability.20 In order to create more robust emitters,
researchers have developed hybrid organic/inorganic nano-
particles from organic dye molecules and amorphous silica. As a
matrix material, silica provides chemical and mechanical
stability, which can protect the encapsulated dye molecules
from external perturbations, while exposing a hydrophilic and
easily functionalized surface to the environment, in some cases
enhancing the photophysical properties of the encapsulated
dyes.21–23
Department of Chemistry, Seoul National University, Seoul 151-747, Korea. E-mail:
jinklee@snu.ac.kr; Fax: +82-2-882-1080; Tel: +82-2-879-2923
† Electronic supplementary information (ESI) available: Reaction conditions for
size-controlled FSNPs, photographs of various mixed conditions of FSNPs with
silicone polymer in acetone solvent, and SEM images of the cross-sectioned
area of the FSNP/silicone polymer composite. See DOI: 10.1039/c3tc30967c
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In this study, we report the synthesis of yellowish-green and (m, 2H), 7.41 (d, 4H), 7.80 (d, 4H). 13C NMR (500 MHz, CDCl3): d
red emitting uorescent organic dye molecules, by facile deriv- ppm 162.2, 147.7, 137.7, 133.2, 130.3, 129.3, 126.1, 117.0, 109.6,
atization of pigment red 254 and rhodamine B with trimethoxy- 44.4. Anal. found: C, 66.02; H, 4.88; N, 5.95%. Calcd for
silane through a consecutive allylation and hydrosilation reac-
tion sequence. These derivatized uorescent dye molecules were
successfully incorporated into silica nanoparticles through the
C24H18Cl2N2O2: C, 65.91; H, 4.15; N, 6.41%.
Synthesis of 3,6-bis(4-chlorophenyl)-2,5-bis(3-(trimethoxy-
silyl)-propyl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione
(PR254H)
¨
Stober method, with the resultant uorescent silica nano-
particles (FSNPs) denoted as SiO2(PR254H) and SiO2(RhBH),
respectively. The two different types of FSNPs showed the similar
optical properties of parent dye molecules. We also fabricated
homogeneous FSNP/silicone polymer composites by dispersing
the FSNPs intoan acetone solvent and mixing in silicone polymer
as the encapsulating material, followed by solvent removal under
vacuum. Moreover, a white light emitting FSNP-based LED was
fabricated by combining FSNP/silicone polymer composites,
incorporated with yellowish-green and red emitting FSNPs, with
a blue InGaN LED. The resulting three-band RGB FSNP-based
WLEDs showed good performances, suggesting that the combi-
nation of highly uorescent FSNPs with LEDs can offer a prom-
ising solution for the manufacturing of white light sources with
high color rendering properties.
PR254A (35 mg, 0.08 mmol) was dissolved in anhydrous CHCl3
(5 mL), followed by the addition of HSi(OMe)3 (0.04 mL,
0.32 mmol) and a catalytic amount of Pt(dvs). The mixture was
stirred at 60 ꢁC for 12 h. Aer cooling to room temperature, the
mixture was immediately ltered through a Celite pad. Solvent
and excess HSi(OMe)3 were removed in vacuo. PR254H was
obtained as orange sticky oil (46 mg, 85%). This compound was
used for the next reaction immediately aer the conrmation of
the disappearance of the allyl moiety in PR254A by NMR.
Synthesis of (9-(2-((allyloxy)carbonyl)phenyl)-6-(diethyl-
amino)-3-xanthenylidene)diethylammonium chloride (RhBA)
RhBA was prepared according to a previous report.23 Rhoda-
mine B (0.5 g, 1.04 mmol), allyl iodide (0.54 g, 3.12 mmol), and
Cs2CO3 (1.02 g, 3.12 mmol) were added in 30 mL of DMF, and
the mixture was stirred at 60 ꢁC for 1 day. Aer cooling to room
temperature, the mixture was extracted with CH2Cl2 and
washed with water (3ꢂ). The CH2Cl2 layer was collected and
concentrated in vacuo, followed by further drying under
vacuum. A dark reddish powder (0.481 g, 88.8%) was isolated by
column chromatography (SiO2, eluent: CH2Cl2/MeOH ¼ 10/1).
1H NMR (500 MHz, CDCl3): d ppm 8.31 (d, 1H), 7.82 (tt, 2H), 7.34
(d, 1H), 7.10 (d, 2H), 6.93 (dd, 2H), 6.80 (d, 2H), 5.70 (m, 1H),
5.20 (dd, 2H), 4.53 (d, 2H), 3.68 (q, 8H), 1.34 (t, 12H). 13C NMR
(500 MHz, CDCl3): d ppm 164.61, 158.62, 157.65, 155.45, 133.48,
133.20, 131.28, 131.19, 131.04, 130.41, 130.18, 129.81, 119.04,
114.30, 113.43, 96.21, 66.02, 46.23, 12.70. HR-MS(FAB+) Calcd
for 483.2642 m/z, Obsd for 483.2640 m/z.
Experimental
Materials
Rhodamine B, allyl iodide, allyl bromide, cesium carbonate
(Cs2CO3), potassium carbonate (K2CO3), chloroform, trime-
thoxysilane (HSi(OMe)3), platinum(0)-1,3-divinyl-1,1,3,3-tetra-
methyldisiloxane complex solution (Pt(dvs)), and N,N-
dimethylformamide (DMF) were purchased from Aldrich.
Pigment red 254 and TEOS (tetraethyl orthosilicate) were
purchased from TCI. Ethanol (EtOH) was purchased from J. T.
Baker. CDCl3 was purchased from Cambridge Isotope Labora-
tories for use as an NMR solvent. Dichloromethane (CH2Cl2),
magnesium sulfate (MgSO4), methanol and ammonium
hydroxide solution (NH4OH) were purchased from Samchun
Chemical Co. All organic solvents were used without any further
purication. SMD 5050 blue LED chip was purchased from
ENTEC L&E Ltd. OE-6560 A/B kit (optical encapsulant) was
purchased from Dow Corning Korea Ltd.
Synthesis of (6-(diethylamino)-9-(2-((3-(trimethoxysilyl)-
propoxy)carbonyl)phenyl)-3-xanthenylidene)diethyl-
ammonium chloride (RhBH)
RhBA (35 mg, 0.07 mmol) was dissolved in anhydrous CHCl3
(5 mL), followed by the addition of HSi(OMe)3 (0.04 mL,
0.28 mmol) and a catalytic amount of Pt(dvs). The mixture was
stirred at 60 ꢁC for 12 h. Aer cooling to room temperature, the
mixture was immediately ltered through a Celite pad. Solvent
and excess HSi(OMe)3 were removed in vacuo. RhBH was
obtained as orange sticky oil (33 mg, 81%). This compound was
used for the next reaction immediately aer the conrmation of
the disappearance of the allyl moiety in RhBA by NMR.
Synthesis of 2,5-diallyl-3,6-bis(4-chlorophenyl)-2,5-dihydro-
pyrrolo[3,4-c]pyrrole-1,4-dione (PR254A)
PR254A was prepared following a procedure similar to that
previously reported.24 Pigment red 254 (86 mg, 0.24 mmol) and
K2CO3 (350 mg, 2.5 mmol) were added to DMF (8 mL). Aer
heating to 130 ꢁC under N2 atmosphere, a solution of allyl
bromide (0.23 mL, 2.8 mmol) in DMF (2 mL) was added drop-
wise and stirred for 5 h at 130 ꢁC. Aer cooling to room
temperature, the mixture was diluted with CH2Cl2 and water.
The mixture was extracted with CH2Cl2 and washed sequentially
with brine (2ꢂ) and water. The organic layer was dried over
MgSO4, ltered, and solvent was removed in vacuo. The residue
General method for synthesizing uorescent silica
nanoparticles
was puried by column chromatography (SiO2, eluent: CH2Cl2) The modied uorescent dye molecules were dissolved in EtOH
1
to afford 58 mg of orange powder in 56% yield. H NMR (500 and H2O, followed by the sequential addition of NH4OH and
MHz, CDCl3): d ppm 4.29 (m, 4H), 5.14 (d, 2H), 5.20 (d, 2H), 5.88 TEOS (solution compositions are found in Table S1†). The
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mixture was stirred at 400 rpm for 12 h at room temperature.
The mixture was centrifuged and the precipitate was redis-
persed in EtOH, followed by centrifugation. This reprecipita-
tion–redispersion procedure was repeated three more times.
The sizes of uorescent silica nanoparticles were controlled by
varying the amounts of TEOS, H2O, and NH4OH.
Fabrication of FSNP-assisted phosphor-converted WLEDs
WLEDs were fabricated by combining InGaN based blue LEDs
with as-synthesized FSNPs and OE-6560 resin. The FSNPs were
dispersed in acetone to avoid aggregation aer mixing with
OE-6560B resin. The mixture solution was blended by vortex
mixing for 15 min until the mixture became transparent. Next,
the acetone was removed in vacuo. The mixture of FSNPs and
OE-6560B resin was further mixed with the OE-6560A resin at a
weight ratio of 1 : 3 (OE-6560A:OE-6560B). The mixture was
well-stirred until it became homogeneous. The mixture was
ꢁ
dropped on a BLED and heated in a vacuum oven at 80 C for
ꢁ
30 min and nally at 170 C for 90 min.
Photostability test
PR254A, RhBA, SiO2(PR254H), and SiO2(RhBH) were dissolved Scheme 1 Schematic illustration of the synthesis of FSNPs.
in various amounts of EtOH such that all solutions possessed
the same UV absorbance. Samples were exposed to UV light
under a Tungsten-Halogen lamp (200 W, PHILIPS) with a light
intensity of 757 mW cmꢀ2. Emission spectra for all samples
were taken aer appropriate illumination times.
(Table S1†). The amount of incorporated RhBH and PR254H
relative to TEOS in generated FSNPs could be estimated to be
about 0.75 and 0.29 mol%, respectively, based on 29Si-NMR and
thermogravimetric analysis (TGA) data (Fig. S1 and S2 and Table
S2†), which were relevant to the mixing percentage of dyes to
TEOS in Table S1† (0.73 and 0.27 for RhBH and PR254H,
respectively).
The photographs of modied uorescent dye molecules
(PR254A and RhBA), SiO2(PR254H) and SiO2(RhBH), respec-
tively, can be clearly observed through the entire dispersion,
suggesting that FSNPs can be well-dispersed in EtOH (Fig. 2a
and b). The UV-vis absorption and photoluminescence spectra
of the uorescent dye molecules and FSNPs are shown in Fig. 2c
and d. SiO2(PR254H) and SiO2(RhBH) exhibited main absorp-
tion bands at 468 nm and 561 nm, respectively. SiO2(PR254H)
had a suitable absorption range from the near-UV to the visible
Characterizations
The absorption and emission of uorescent organic dye mole-
cules and FSNPs were measured by UV-Vis spectrometry (Sinco,
S-3100) and uorophotometry (JASCO, FP-6500), respectively, at
1
room temperature. The synthetic dye was characterized by H-
and 13C-NMR (Varian NMR System 500 MHz), mass spectrom-
etry (JEOL, JMS-AX505WA), and elemental analysis (CE Instru-
ment, Flash2000). The size and shape of silica nanoparticles
were characterized by transmission electron microscopy (TEM)
(Hitachi, H-7600). The EL spectra, the CIE chromaticity coor-
dinates, and the CRI values of the as-fabricated FSNP-LED were
collected by a quantum efficiency measurement system (QE-
2000, Photal OTSUKA ELECTRONICS) at room temperature.
Results and discussions
The overall scheme for the synthesis of FSNPs is described in
Scheme 1. Trialkoxysilyl terminal groups could be directly
introduced into the uorescent dye molecules by the sequential
allylation and hydrosilation reactions. These allyl terminal
groups in the derivative dye molecules could then be quantita-
tively converted into trialkoxysilyl groups by hydrosilation in the
presence of catalytic Pt(dvs). Two types of modied uorescent
dye molecules were successfully incorporated into silica nano-
particles by co-condensation with TEOS in basic ethanol solu-
tion with NH4OH (Fig. 1). The size of the FSNPs could be
controlled in the range from 20 to 130 nm by varying the
Fig. 1 TEM images of FSNPs: (a) 20 nm; (b) 50 nm; (c) 80 nm of SiO2(PR254H);
concentration of TEOS, water and ammonia in ethanol solution and (d) 30 nm; (e) 50 nm; (f) 130 nm of SiO2(RhBH).
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region. Generally, UV (360–410 nm) or blue light (420–480 nm)
LEDs are used as light sources for WLEDs; therefore, broad
absorption is an advantage of the organic dye-encapsulated
silica nanoparticles. The photoluminescence maximum was
red-shied from 532 nm for PR254A to 547 nm for the
SiO2(PR254H) nanoparticle when excited at 450 nm. In the case
of the SiO2(RhBH), the maximum photoluminescence wave-
length also red-shied from 588 nm for RhBA to 601 nm for the
SiO2(RhBH) nanoparticle. The red-shi of the emission band to
longer wavelengths as well as bandwidth change in PL spectra
was very likely due to the difference in environmental properties
such as hydrogen bonding and polarity between the solvent and
silica matrix as reported in the literature.25–28 This red emission
helps wide expression and would lead to a high CRI of white
emission. With excitation at 450 nm, SiO2(PR254H) had a
photo-luminescence maximum at 547 nm, which overlaps with
the absorption of SiO2(RhBH). It is expected that some of the
emission energy of SiO2(PR254H) would transfer to SiO2(RhBH)
if they are both incorporated into a system.
Fig. 3a and b show the maximum photoluminescence
intensity as a function of light exposure time for photostability
verication. Modied uorescent dye molecules were subject to
photobleaching in the EtOH solution by a tungsten halogen
lamp excitation. The photoluminescence intensity of the
PR254A decreased to approximately 50% from the initial
intensity aer 5 h of exposure time, indicating that the dye is
discolored because of photodegradation. However, RhBA
retained its photoluminescence of approximately 90% aer
30 h. It is worthy to note that, owing to their excellent photo-
stability and photophysical properties, rhodamine dyes are
Fig. 3 (a) Photostability of fluorescent dye molecules and FSNPs as a function of
light exposure time.
widely used as laser dyes, uorescence standards (for quantum
yield and polarization), pigments, and uorescent probes.29 In
the case of the FSNPs, the photoluminescence intensity is
maintained or slightly increased at the initial state. Because
these dye molecules are chemically bound to the silica matrix,
they cannot be easily removed by extracting with a large amount
of solvent or applying sonication; furthermore they are not
easily photo-bleached as reported in the literature because of
the restricted movement of dye molecules aer being
embedded in the silica matrix.22,23,30 These properties make
uorescent silica nanoparticles very useful for WLED
applications.
To adopt FSNPs as light conversion materials in LEDs, it is
necessary to homogeneously disperse FSNPs into a polymer
matrix for the fabrication of FSNP/silicone polymer compos-
ites.31 Matrix dispersion may inuence the uniformity of light
that is emitted from an LED device, depending on the viewing
angle.7 Therefore, the FSNPs were dispersed in acetone solvent
Fig. 4 (a) EL spectra and (b) CRI of the as-prepared FSNP-based WLEDs under
different forward bias currents; (c) CRI of the as-prepared FSNP-based WLEDs.
Insets show photographs of the as-prepared FSNP-based WLED (460 nm InGaN
blue LED chip encapsulated with FSNPs (547 nm and 601 nm)/silicone polymer
composite) and the FSNP-based WLED operated at 80 mA; (d) thermal stability of
the FSNP/silicone polymer composite film by monitoring the photoluminescence
intensity as a function of heating time at 120 ꢁC.
Fig. 2 (a) Photographs of red and yellowish-green fluorescent organic dye
molecules and (b) FSNPs under UV excitation at 365 nm; (c) normalized UV-vis
absorption; and (d) photoluminescence spectra of PR254A, RhBA, SiO2(PR254H)
and SiO2(RhBH) in EtOH.
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and mixed with a silicone polymer instead of a dry FSNP powder 460 nm, 533 nm, and 594 nm, respectively. Accordingly, the
to prevent aggregation of nanoparticles (Fig. S3 and S4†). These RGB emission band intensities of the underlying blue LED chip
composites were applied as light conversion materials onto a can be tuned by varying the amount of FSNPs incorporated in
blue InGaN LED. Fig. 4c inset shows photographs of the as- the silicone polymer.
prepared and white light emitting FSNP-based WLEDs operated
By controlling the concentration and the SiO2(PR254H)/
at a current of 80 mA to obtain a clear emission image of the SiO2(RhBH) ratio, various LEDs were fabricated with a CRI
fabricated FSNP-based WLED. Bright white light was emitted ranging from 75 to 85 (Fig. 5 and Table 1). In addition, the color
from the as-prepared FSNP-based WLED with a CRI (Ra) of 86.7 temperature was easily tuned from 3783.1 K to 17 042.2 K and
under a forward bias current of 80 mA, which is much higher the CIE color coordinates of various FSNP-based LEDs could be
than that of the YAG:Ce-based commercial WLEDs (Ra ꢃ 70). It easily controlled as shown in Fig. 5 and Table 1. The FSNP-
also showed the Commission Internationale de l'Eclairage (CIE) based WLED was found to have a higher CRI compared to the
color coordinates of (0.33, 0.33) and a color temperature (Tc) of YAG-based WLED, as the combination of SiO2(PR254H) and
5452.6 K, corresponding to warm white light. As shown in SiO2(RhBH) compensates for the poor emission of the YAG
Fig. 4b and c, the CIE coordinates and CRI of the FSNP-based phosphor in the red and green regions. An explanation for why a
WLED under different currents changed only slightly, which large amount of SiO2(PR254H) is required compared to
indicates a good PL stability of the FSNP-based WLEDs. The SiO2(RhBH) for white emission follows: because of the overlap
long-term thermal stability of the FSNP/silicone polymer of the emission band of SiO2(PR254H) and the absorption band
composite was also investigated (Fig. 4d). It was observed that of SiO2(RhBH), the green emission from SiO2(PR254H) is
the original photoluminescence of the FSNP/silicone polymer reabsorbed by SiO2(RhBH) (Fig. 2c and d, and 4a). When green
composite was maintained and even slightly increased at and red dyes are in close enough proximity, energy transfer
ꢁ
120 C, supporting the effectiveness of FSNPs for LED applica- occurs from green to red and photoluminescence overlaps. The
tion along with photochemical stability as shown in Fig. 3. The remaining green dyes, which are not involved in energy transfer,
electroluminescence (EL) spectra of the as-fabricated FSNP- emit a green emission around 532 nm.
based WLED under different forward bias currents are shown in
Fig. 4a, in which the emission peaks of the blue LED chip, the
yellowish-green and red light-emitting FSNPs were located at
Conclusions
FSNPs, in which two types of dyes are covalently incorporated
into silica nanoparticles, have been successfully synthesized
¨
using the Stober method. The obtained nanoparticles have a
broad absorption in the near-UV to blue region and a broad
emission, thereby achieving wide color expression. The modi-
ed uorescent dye molecules that are covalently attached to
silica nanoparticles have better photostability and less photo-
dependent photoluminescence. The FSNP/silicone polymer
composite also shows excellent long term thermal stability at
120 ꢁC. By controlling the portions of red and green species, the
FSNPs exhibit broad color tunability and a high CRI for white
emission from a blue LED. These results demonstrate that the
uorescent dye molecules with an appropriate structure could
replace phosphors for LED applications. The described photo-
stable FSNPs potentially allow for new WLED designs, in place
of inorganic phosphor-based LEDs, for direct and simple
fabrication of lighting devices with superior performance.
Fig. 5 EL spectra of various FSNP-based LEDs with various compositions of wt%
and R/G ratios: (a) 5 wt%, R : G ¼ 1 : 15; (b) 5 wt%, R : G ¼ 1 : 20; (c) 10 wt%,
R : G ¼ 1 : 15, and; (d) 10 wt%, R : G ¼ 1 : 20.
Acknowledgements
This research was supported by an industrial grant from Sam-
sung Electronics Co., Ltd. H.-S. J. and Y.-J. K. gratefully
acknowledge the BK21 fellowship.
Table 1 The CIE color coordinates, color rendering index (Ra), and color
temperature (Tc) of various FSNP-based WLEDs
Notes and references
Weight%
R to G ratio
CIE (x, y)
Ra
Tc (K)
1 J. Y. Tsao, Light Emitting Diodes (LEDs) for General
Illumination—An OIDA Technology Roadmap Update,
2002, http://www.netl.doe.gov/ssl/PDFs/Report%20led%20
November%202002a_1.pdf.
A
B
C
D
5
1 : 15
1 : 20
1 : 15
1 : 20
(0.2565, 0.2667)
(0.2658, 0.2825)
(0.3434, 0.3499)
(0.4067, 0.4342)
76.5
80
85.4
75.5
17 042.2
12 421.6
5060.8
10
3783.1
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5884 | J. Mater. Chem. C, 2013, 1, 5879–5884
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