Full text of DOI:10.1557/JMR.2003.0294

Laser-controlled precipitation of gold nanoparticles in
silicate glasses
Xiongwei Jiang, Jianrong Qiu, Huidan Zeng, and Congshan Zhu
Photon Craft Project, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences
and Japan Science and Technology Corporation, Shanghai 201800, People’s Republic of China
(Received 13 February 2003; accepted 9 June 2003)
We report on the observation of space-selective precipitation of gold nanoparticles in
Au2O-doped silicate glass by a method of irradiation with an 800-nm femtosecond
laser and further heat treatment. The irradiated region of the glass first became gray in
color after irradiation with the femtosecond laser and then turned red after further heat
treatment at around 520 °C, indicating that gold nanoparticles have precipitated in the
irradiated region of the glass. A possible mechanism has been suggested that the Au+
ions in the region irradiated are reduced to Au0 atoms by the femtosecond laser, and
then the Au0 atoms accumulate to form gold nanoparticles with the glass sample heat
treated. The observed phenomenon should have potential applications in the fabrication
of ultrafast all-optical switches.
precipitation of silver nanoparticles inside glass.11 Nice
I. INTRODUCTION
butterflies, yellow in color, composed of silver nanopar-
ticles, were drawn inside the glass sample. In the end of
the paper of Ref. 11, it is mentioned that gold nanopar-
ticles can also be induced to space-selectively precipitate
inside glass, but no details were provided.
In this paper, we report in detail on the space-selective
precipitation of gold nanoparticles in Au+ doped silicate
glasses using a method identical to that in Ref. 11. We
observed that gold nanoparticles, red in color, could be
precipitated anywhere inside the glass with the help of a
femtosecond laser. Other interesting phenomena have
been observed in the Au+ doped glass, such as the varia-
tion of the color of gold nanoparticles with the intensity
of the laser and laser-induced dissolution of gold nano-
particles preformed in the glass, which are now being
studied and will be reported latter.
Gold nanoparticles, used for more than 300 years in
the coloration of glass to obtain so-called gold ruby
glass,1 have again aroused the interests of scientists be-
cause of their unique optical properties,2–4 such as non-
linear optical properties and ultrafast nonlinear response,
which are different from those of bulk gold as well as
those of individual gold atoms or ions. Materials doped
with gold nanoparticles have a large optical absorption
coefficient due to the surface plasmon resonance of gold
nanoparticles in wavelengths from 500 to 560 nm, and
consequently strong enhancement of the third-order non-
linear optical susceptibility (␹(3)) has been observed
around the peak of the absorption band.
Glasses, with the advantages of being transparent and
able to be made in bulk materials, have been used as base
materials to dope gold nanoparticles. Extensive studies
have been made on the fabrication of the glass doped
with gold nanoparticles.5,6 Conventional methods used to
obtain glasses containing gold nanoparticles fabricate
Au+-doped glasses through traditional melting or ion-
exchange techniques, combined with heat treatment or
ionizing radiation of the glasses to precipitate gold nano-
particles. Other techniques, such as sol-gel, chemical va-
por deposition, sputtering, and ion implantation,7–10 are
also widely used in the fabrication of the glass doped
with gold nanoparticles. However, it is not easy to space-
selectively control the precipitation of gold nanoparticles
in glasses by using these methods. Recently, we first
used a new method combining the irradiation of a fem-
tosecond laser and successive heat treatment to produce
silver nanoparticles and succeeded in the space-selective
II. EXPERIMENTAL
The composition of the glass sample studied was
70SiO2 · 20Na2O · 10CaO doped with 0.01Au2O
(mol%). Regent-grade SiO2, Na2CO3, CaCO3, and
AuCl3 · HCl · 4H2O were used as starting materials. The
batch was melted in a platinum crucible at 1500 °C for
2 h under the ambient atmosphere. Then the melt was
poured onto a stainless module kept at room temperature,
and quenched into transparent and colorless glass. The
glass was annealed at 500 °C for 1 h. Glass samples were
obtained by cutting and polishing the glass to a thickness
of 3 mm.
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X. Jiang et al.: Laser-controlled precipitation of gold nanoparticles in silicate glasses
A Ti:sapphire laser (800 nm, 120 fs, 1 KHz) was used
Fig. 1. The absorption bands at 620 nm, and at 430 and
320 nm can be ascribed to electron-trapped color centers
and hole-trapped color centers, respectively.14
in our experiments. The maximum average output power
was 700 mW. The laser beam with an average power of
130 mW was focused by a 5× objective lens with a
numerical aperture of 0.13 into the interior of the glass
sample, which was put on an XYZ stage. The XYZ stage
was controlled by a computer and could move in three di-
mensions with a precision of 100 nm at different speeds.
A spectrophotometer (JASCO V-570, Japan) was used to
measure the absorption spectra of the glass samples.
Electron spin resonance (ESR) was recorded with a spec-
trometer (Bruker ESP 300E, Germany), which was op-
erated at X-band microwave frequency (∼9.68 GHz).
For the convenience of the following measures, an
irradiated area of 4 × 10 mm was obtained by focusing
the laser into the glasses and translating the glasses to-
and-fro at a speed of 2.5 mm/s and with a line interval of
20 ␮m along the direction perpendicular to the incident
laser beam.
After the irradiation of the laser, the glass sample was
heat treated at different temperatures between room tem-
perature and 600 °C, resulting in further changes in the
color of the glass with the temperature. The changes fall
into two major steps, which are the disappearance of the
color centers with temperatures lower than 300 °C and
the appearance of red color with annealing temperatures
higher than 500 °C.
Figure 2 shows the variation of the absorption of the
irradiated glass with the temperature between room tem-
perature and 300 °C. The absorption bands at 430 and
620 nm gradually decrease as the temperature increases
from room temperature, and totally disappear at the tem-
perature of 300 °C. The disappearance of the absorption
bands at 430 and 620 nm results from the decomposition
of the color centers, which are thermally unstable at sev-
eral hundred degrees centigrade.
Further heat treatment at a higher temperature can
result in another change in the color of the glass. A color of
red starts to appear in the irradiated area of the glass with
the temperature reaching 500 °C, and the intensity of the
color increases with the increase of annealing temperature
until 600 °C. Figure 3 shows the change of the absorption
of the glass in the irradiated area corresponding to the
change in the color of the glass. Since the gold nanopar-
ticles have a characteristic absorption band in the wave-
length range of 500–560 nm due to the surface plasmon
absorption of gold nanoparticles,15 the appearance of the
III. RESULTS AND DISCUSSION
With the glass irradiated by the laser, an obvious
change in color from colorless to gray was observed in
the irradiated area of the glass. Figure 1 shows the dif-
ference in absorption between the original and irradiated
glass. The absorption of the glass in the irradiated area
increases greatly in the wavelength range of 260–
800 nm, arising from the color-center generation induced
by the laser.12,13 Three absorption bands, with peaks at
320, 430, and 620 nm, respectively, can be observed in
FIG. 1. Absorption spectra and induced absorption spectra of Au+-
doped silicate glass: curve (a) original glass; curve (b) irradiated by
femtosecond laser; and curve (c) difference between curves (a) and (b).
FIG. 2. Absorption spectra of Au+ doped silicate glass (a) before and
(b) after femtosecond laser irradiation, and after further heat treatment
at (c) 200 °C and (d) 300 °C for 30 min.
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X. Jiang et al.: Laser-controlled precipitation of gold nanoparticles in silicate glasses
absorption band peaking at 500 nm, which is observed in
Fig. 3 [curve (c)], is indicative of the precipitation of gold
nanoparticles in the glass irradiated by the laser.
trapped by Au+ ions to form Au0 atoms. Therefore, we
believe that the Au+ ions near the focus point of the laser
have been reduced to Au0 atoms with the irradiation of
Figure 4 shows the ESR spectra of the Au+-doped
silicate glass irradiated by the femtosecond laser as well
as the variation of ESR spectra with the temperature of
the heat treatment. A strong signal, which is due to the
hole trap centers induced by femtosecond laser,11,16 was
observed after the glass irradiated by the femtosecond
laser [curve (a)]. The hole-trap centers are the same as
those induced in the soda-lime-silicate glasses by ultra-
violet light or x-ray.14 The signal of ESR centers be-
comes weaker as temperature increases, and no signal is
observed in the glass sample with the annealing tempera-
ture higher than 300 °C. Therefore, the variation of ESR
spectra with annealing temperature demonstrates that the
radiation defects of hole-trap centers are decomposed in
the heat treatment of the glass at a temperature of several
hundred degrees centigrade. This result is in good agree-
ment with the decomposition of the color centers upon
heat treatment, concluded from the measurement of ab-
sorption spectra of the glass.
Here are some considerations on the mechanism of the
precipitation of gold nanoparticles. On the irradiation of
the Au+-doped silicate glass by the focused femtosecond
laser, nonlinear absorption occurs near the focus point of
the laser with an ultrahigh power density,12 resulting
in the generation of free electrons from 2p orbital of
nonbridging oxygen. The free electrons, while they travel
in the glass matrix, will be trapped by structural defects
to form color centers, and more importantly, will be
the laser.
laser
glass matrix → h+ + e−
,
(1)
(2)
(3)
h+ or e− + structural defects → color-centers
e− + Au+ → Au0
,
.
In heat treating the glass sample irradiated by the laser,
the electron-trapped color centers were stimulated ther-
mally and released to free electrons again. These elec-
trons may also be trapped by Au+ ions, but most of them
recombined with holes and then disappeared. This results
in the bleaching of the glass at 300 °C because of the
decomposition of color centers. As the temperature in-
creases, the mobility of pre-formed Au0 atoms increases,
which will lead to the increase of the diffusion of the
atoms as well as the final aggregation of them. As to
this case, when the temperature of the heat treatment
reaches 500 °C, gold nanoparticles red in color begin to
appear in the irradiated area of the glass. Since the dif-
fusion of Au0 atoms relates with the time and the tem-
perature of the heat treatment, more gold nanoparticles
form when the irradiated glass is heat treated at a higher
temperature or for a longer time at the temperature range
from 500 to 600 °C. However, there are still some ques-
tions left unclear. For example, according to our expla-
nations of the mechanism of the gold nanoparticles
formation process, there should be a lot of hole-trapped
color-center left in the glass matrix for the trapping of
electrons by Au+. However, no signal corresponding to
FIG. 4. ESR spectra of Au+ doped silicate glass (a) after irradiation of
femtosecond laser and after further heat treatment at (b) 100 °C and
(c) 200 °C for 30 min.
FIG. 3. Absorption spectra of Au+-doped silicate glass after femto-
second laser irradiation and further heat treatment at (a) 500 °C,
(b) 520 °C, and (c) 540 °C for 30 min.
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X. Jiang et al.: Laser-controlled precipitation of gold nanoparticles in silicate glasses
induce any graphics as well as arrays of red dots inside
the glass, which can be used in the fabrication of three-
dimensional colored industrial art objects and optical
memory.
IV. CONCLUSIONS
Gold nanoparticles have successfully been space-
selectively precipitated in Au+ doped silicate glass. The
precipitation of gold nanoparticles is considered to be
due to the femtosecond laser-induced reduction of Au+
ions and consequent thermally driven aggregation of
Au0 atoms upon heat treating. This method provides us
a new chance to obtain functional microstructures with
a high third-order nonlinear optical susceptibility
inside glass.
ACKNOWLEDGMENT
This work was partially supported by National Natural
Science Foundation of China under Grant Nos. 50125258
and 50072037.
FIG. 5. Photograph of Au+ doped glass after irradiation of femtosec-
ond laser and heat treatment at 540 °C for 30 min.: (a) irradiated area,
(b) unirradiated area.
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