SUPPLEMENTAL MATERIAL
White-blue electroluminescence from a Si quantum dot hybrid LED
Yunzi Xin,1 Kazuyuki Nishio,1 and Ken-ichi Saitow1,2
1Department
of Chemistry, Graduate School of Science, Hiroshima University, Higashi-hiroshima, 739-
8526, Japan
2Natural
Science Center for Basic Research and Development (N-BARD), Hiroshima University, Higashi-
hiroshima, 739-8526, Japan
DLS data was obtained from the Si QDs dispersed in 2-propanol, whereas the TEM
data was collected by dropping the 2-propanol dispersion onto TEM grids (High Resolution
Carbon Grid, STEM Cu100P, Okenshoji Co. Ltd.). In present work, we optimized the DLS
measurement conditions for Si QDs on Malvern Zetasizer nano (green laser) system. Namely,
the concentration of Si QDs solution is adjusted till the software reports a size distribution
result with good quality. Similar DLS size distribution of Si QDs could be obtained 13 times.
DLS and TEM results are shown as Fig S1.
Figure S1. Size distribution data for Si QDs as determined by (a and b) DLS and (c and d) TEM.
1
FTIR spectrum was measured by dropping 2-propanol dispersion of Si QDs on ATR
prism. The spectrum was corrected by substituting the background IR spectrum of 2-propanol
from the Si QDs solution. Fig. S2 presents the FTIR spectrum of synthesized Si QDs. Si-C
stretching modes are observed at 1465, 1250, and 660 cm-1. Peak at 3000 cm-1 is assigned to
stretching mode of -CH2 and -CH3, and 1383 cm-1 is related to the bending mode of -CH3.
The bands at 1160, 1130, and 815 cm-1 were assigned to Si-O related vibration mode. And the
stretching mode of -OH was obtained at 3000 cm-1.1
Figure S2. FTIR spectrum of Si QDs.
As a sample preparation for XPS measurement, the Si QD dissolved in 2-propanol
was deposited on ITO substrate and the substrate was dried in Ar-filled glove box. Figure S3
shows XPS spectra of Si QDs as thin film. As displayed in Fig. S3(a), four bands at 100.6,
101.9, 102.9 and 104.1 eV are observed as 2p spectrum by Gaussian fitting and are attributed
to the different species from S+ , Si2+, Si3+, to Si4+, respectively.2 For XPS spectrum of C 1s,
two bands at 286.5 and 284.8 eV are assigned to Si-C and C-C, C-H bonding, respectively.3
Figure S3. XPS spectra of (a) Si 2p and (b) C 1s.
2
Using a commercial spectrophotometer (HAMAMATSU, QUANTAURUS-QY), we
measured X, Y, Z tristimulus values of PL of Si QDs solution at the excitation wavelength of
365 nm. Obtained values are in the following.
𝑋 = 272.6, 𝑌 = 362.8, 𝑍 = 506.7
Then, the (x, y) coordinate shown in Fig. 1(b) is changed into the chromaticity coordinate of
(r, g, b) by following procedure. According to the reported papers,4,5
𝑋
0.49
[𝑌 ] = 0.17697 [0.17697
𝑍
0.00
0.31
0.81240
0.01
0.20
𝑅
0.01063] ∙ [𝐺 ],
0.99
𝐵
where R, G, B can be derived using the inverse matrix. Thus, R, G, B tristimulus values are
estimated as,
𝑅 = 14.558, 𝐺 = 74.688, 𝐵 = 89.825.
Utilizing these values, the chromaticity coordinate (r, g, b) is obtained as,
𝑟=
𝑅
= 0.081
𝑅+𝐺+𝐵
𝑔=
𝐺
= 0.417
𝑅+𝐺+𝐵
𝑏=
𝐵
= 0.502
𝑅+𝐺+𝐵
.
3
The electronic absorption spectrum was recorded by depositing Si QDs from its 2propanol solution on quartz glass, followed by drying process in Ar-filled glove box. The
direct transition bandgap is obtained by analyzing the absorption spectrum with Tauc’s low,6
as shown in Fig S4.
Figure S4. Tauc plot as direct transition of Si QD (inset: electronic absorption
spectrum of Si QDs).
Figure S5. Current-voltage curves of the reference organic-only LED.
(b)
4
REFERENCES
1
T. Kitasako and K. Saitow, Appl. Phys. Lett. 103, 151912 (2013).
2
M. J. L. Portolés, R. P. Diez, M. L. Dell’Arciprete, P. Caregnato, J. J. Romero, D. O.
Mártire, O. Azzaroni, M. Ceolín and M. C. Gonzalez, J. Phys. Chem. C 116, 11315 (2012).
3
D. Tan, Z. Ma, B. Xu, Y. Dai, G. Ma, M. He, Z. Jin and J. Qiu, Phys. Chem. Chem. Phys.
13, 20255 (2011).
4
H. S. Fairman, M. H. Brill and H. Hemmendinger, Color Research and Application 22, 12
(1997).
5
M. H. Brill, Color Research and Application 23, 259 (1998).
6
J. Tauc, Mat. Res. Bull. Vol. 3, 37 (1968).
5