Supporting Information
Broadband plasmonic silver nanoflowers for
high performance random lasing covering
visible region
Qing Chang# , Xiaoyu Shi # , Xuan Liu, Junhua Tong, Dahe Liu and Zhaona Wang*
Applied Optics Beijing Area Major Laboratory, Department of Physics, Beijing Normal University,
Beijing, 100875, China
†Electronic supplementary information (ESI) available: Materials and methods, Figure S1–6.
*
Email: [email protected]
#
These authors contributed equally to this work
Contents:
A: XRD patterns of Ag NFs fabricated under different concentration of PVP
B: Enhancement effect of electromagnetic field of Ag NFs
C: Extinction property of Ag NF
D: Experiment set-up for random laser systems
E: Stability of the silver nanoflowers and the threshold of Ag NF-based random lasers
F: Spectra and threshold characteristics of random systems with different size Ag NFs
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A: XRD patterns of Ag NFs fabricated under different concentration of PVP
To resolve the crystallinity and structure of the bulk nanoporous Ag NFs as fabricated, powder
X-ray diffraction (XRD) is employed as shown in Figure S1. The relative intensities of
diffraction peaks for all samples differ with standard powder diffraction data. The peak
intensity ratio of (111):(200) diffraction is among 3.18 and 3.73 for the as-prepared Ag NFs,
which is bigger than 2.5, the intensity ratio of the standard Ag diffraction database. The result
indicates that Ag NFs exhibit a preferred orientation along the (111) plane, whereas solid
silver nanoparticles demonstrate random growth due to the differences in multiple relative
intensities compared with standard Ag data.
Figure S1. XRD patterns of the Ag NFs fabricated from different PVP concentrations of 23
mM, 46 mM, 115 mM and 137 mM, respectively.
B: Enhancement effect of electromagnetic field of Ag NFs
The normalized electric-field distribution near the Ag NFs is simulated by using simple
models with the commercial software COMSOL. In simulations, the permittivity of Ag is
chosen from Johnson and Christy’s experiments.[1] The incidental plane wave source is
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polarized along y axis and transmitted along z axis. The Ag NF models of 500 nm and 800 nm
for the diameter size are shown in Figure 3a. For the 500 nm Ag NF, it composes of 62
hemispheres with the diameter of 100 nm and a core sphere with the diameter of 400 nm. For
the 800 nm Ag NF, it composes of silver nanocuboids distributed radially. The nanocuboid is
400 nm in length, and 80 nm in both width and height, intersection angle is both 30º in the
plane of X0Z0 and X0Y0. The electric distributions of Ag nanoparticles at YZ panel are
calculated at different incidental wavelength of 435 nm, 540 nm, 575 nm and 640 nm, which
are in the luminescence band of Coumarin 440, Coumarin 153, rhodamine 6G and Oxazine.
The electric distributions of the 500 nm Ag nanosphere at YZ panel in Figure S2 shows that
the field enhancement factor (FEF) of 500 nm Ag NFs are 31.5 (at 435 nm), 19.8 (540 nm),
11.5 (at 575 nm) and 9.5 (at 640 nm), which are all bigger than that of the simple Ag
nanosphere under the corresponding wavelengths. The maximum FEF is enhanced by 7 times
at 435 nm by nanogaps. As the diameter of Ag NFs increased to 800 nm (in Figure S3), the
FEF are 44 (at 435 nm), 19.7 (540 nm), 36 (at 575 nm) and 20.2 (at 640 nm), respectively.
The maximum field EF is enhanced by 9.94 times regarding to that of the simple Ag
nanosphere at 575 nm. It can be clearly seen that the local field can be greatly enhanced by
hot spot effect induced by the nanogaps. In addition, the FEFs of 800 nm Ag NFs are almost
larger than that of 500 nm Ag NF, while the FEFs of Ag nanospheres with different sizes are
nearly constant. We can obtain that the lager the Ag NFs are, the more nanogaps and spiky
tips the Ag NFs possess, and thus the bigger enhancement factor will be provided by the Ag
NFs.
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Figure S2. Electric field distribution of 500 nm nanoparticles. Silver nanosphere (a-d) and
Ag NF (e-h) illuminated under the wavelengths of 435 nm (a,e), 540 nm (b,f), 575 nm (c,g)
and 640 nm (d,h), respectively.
Figure S3. Electric field distribution of 800 nm nanoparticles. Silver nanosphere (a-d) and
Ag NF (e-h) illuminated under the wavelengths of 435 nm (a,e), 540 nm (b,f), 575 nm (c,g)
and 640 nm (d,h), respectively.
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C: Extinction property of Ag NF
The extinction cross section (σect) has also been calculated by σect =σabs +σsca, where σabs and
σsca is absorption cross section and scattering cross section. Figure S4 show the broadband
extinction spectra of the Ag NF, verifying the Ag NF with abundant nanogaps can enhance
the local electromagnetic field over the whole visible range.
Figure S4. Extinction property of Ag NF. The computed extinction cross section of 500 nm
Ag NF and 800 nm Ag NF.
D: Experimental set-up for random laser systems
The experimental set-up of the random laser system is shown in Figure S5. The mixed
suspension is collected in a cuvette of length 20 mm, width 10 mm and height 45 mm. The
dye system is then pumped vertically using a Q-switched frequency-doubled Nd:YAG pulsed
laser (Continuum PowerLite Precision 8000) , a pulse duration of 8 ns, a repetition rate of 10
Hz and an out-beam diameter of 8 mm, the wavelength is chosen as 532 nm for the dye R6G
and 355 nm for the dyes C440 and C153. The 570 nm nanosecond pulses is generated by
Optical Parametric Oscillators pumped by a Q-switched Nd:YAG pulsed laser to excite the
dye Oxazine. The emission spectra of the random lasing systems are collected horizontally by
a Princeton Instruments Acton SP 2750 spectrometer with a high resolution of 0.01 nm.
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Figure S5. Experimental set-up for random laser systems.
E：Stability of the Ag NF-based random lasers
Figure S6a shows the SEM images of the Ag NFs (CPVP = 46 mM) stored in DI water after
one year, demonstrating the same morphology to the new synthesized Ag NFs (seen in Figure
1b and 1f) in shape and size. Furtherly, the threshold stability of the Ag NFs based random
lasers are carefully shown in Figure S6b by measuring the corresponding threshold of the
stored Ag NFs at different time, displaying a stable threshold behavior with little fluctuations
around 0.24 MW cm-2 which is the same as that of the random laser shown in Figure 5b. The
good stability shows that the Ag NFs are the excellent scatterers in random lasers.
Figure S6. Stability of the Ag NF-based random lasers. (a) SEM images of Ag NFs stored
in DI water after one year. (b) The corresponding threshold of stored Ag NFs based random
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system.
F: Spectra and threshold characteristics of random systems with different size Ag NFs
Figure S7 depicts typical spectra observed from samples with different sizes (1200 nm (a,b),
800 nm (c,d) and 500 nm (e,f) 360 nm (g,h), 300 nm (i,j)) by varying pump power densities.
When the diameter of Ag NFs is 1200 nm, there appear several sharp spikes with line widths
of sub-nanometer (Figure S7a) when the pump power surpasses the threshold of Eth = 0.4 MW
cm-2 (Figure S7b). As the pump power density further increases, there are more peaks
emerged in the spectrum. Similar phenomena are observed in other random systems with the
Ag NFs in the diameter of 800 nm (Figure S7c), 500 nm (Figure S7e), 360 nm (Figure S7g)
and 300 nm (Figure S7i). The corresponding thresholds are 0.28 MW cm-2 (Figure S7d), 0.30
MW cm-2 (Figure S7f), 0.35 MW cm-2 (Figure S7h) and 0.30 MW cm-2 (Figure S7j), which is
considerably low for random lasers. The property of coherent lasing and low threshold is a
consequence of the strong gain provided by the nanogaps within the Ag NFs.
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Figure S7. Effect of scatterers’ diameter on the performance of random lasers. Spectra
and threshold characteristic of random system composed of R6G (0.15 mg ml-1) and Ag NFs
with the diameter of 1000 nm (a,b), 800 nm (c,d) and 500 nm (e,f) 360 nm (g,h), 300 nm (i,j),
respectively.
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REFERENCES
[1] Johnson PB, Christy RW. Optical Constants of the Noble Metals. Phys Rev B 1972; 6:
4370-4379.
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