Poly{[4-(hydroxy)(tosyloxy)iodo]styrene}-promoted direct α-hydroxylation of ketones to α-hydroxyketones

Article abstract of DOI:10.1016/j.jlumin.2005.09.015

Poly{[4-(hydroxy)(tosyloxy)iodo]styrene} was efficient in the α-hydroxylation reaction of ketones to afford α-hydroxyketones in dimethyl sulfoxide-water. The polymer reagent could be regenerated and reused.

Full text of DOI:10.1016/j.jlumin.2005.09.015

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Journal of Luminescence 121 (2006) 32–38
www.elsevier.com/locate/jlumin
Controlled synthesis and relationship between luminescent
properties and shape/crystal structure
2
+
of Zn SiO :MN phosphor
2
4
Ã
Junxi Wan, Zhenghua Wang, Xiangying Chen, Li Mu, Weichao Yu, Yitai Qian
Hefei National Laboratory for Physical Sciences at Microscale and Department of Chemistry,
University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China
Received 3 May 2005
Available online 4 November 2005
Abstract
Mn-doped Zn SiO phosphors with different morphology and crystal structure, which show different luminescence
4
2
and photoluminescence intensity, were synthesized via a low-temperature hydrothermal route without further calcining
treatment. As-synthesized zinc silicate nanostructures show green or yellow luminescence depending on their different
crystal structure obtained under different preparation conditions. The yellow peak occurring at 575 nm comes from the
b-phase zinc silicate, while the green peak centering at 525 nm results from the usual a-phase zinc silicate. From
2 4 2 4
photoluminescence spectra, it is found that Zn SiO nanorods have higher photoluminescence intensity than Zn SiO
nanoparticles. It can be ascribed to reduced surface-damaged region and high crystallinity of nanorods.
r 2005 Elsevier B.V. All rights reserved.
PACS: 78.66.J; 78.60
Keywords: Fluorescence spectroscopy; Luminescence; Silicates; Crystal growth; Nanostructures
1
. Introduction
inorganic 1D systems exhibit a wide range of
optical and electrical properties [5]. Quantum
confinement of electrons in 1D system provides a
powerful tool for manipulating their optical,
electrical, and thermoelectrical properties [6,7].
Most of these functions depend strongly on the
chemical composition and crystal structure of
materials. Novel properties would be obtained
while the crystal structure of host materials was
changed. However, size and dimensionality are
Recently, much research has been focused on
the synthesis and characterization of one-dimen-
sional (1D) nanomaterials [1–4]. Nanometer-sized
Ã
Corresponding author. Tel.: +86 551 3606647;
fax: +86 551 3607402.
E-mail addresses: wanjx@mail.ustc.edu.cn (J. Wan),
ytqian@ustc.edu.cn (Y. Qian).
0022-2313/$ - see front matter r 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jlumin.2005.09.015

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J. Wan et al. / Journal of Luminescence 121 (2006) 32–38
33
now regarded as particularly important factors
influencing the chemical and physical properties of
the materials [8]. If materials were prepared in the
form of a 1D nanostructure, they would be
expected to be highly functionalized materials as
a result of both shape-specific and quantum
confinement effects, acting as electrically, magne-
tically, or optically functional host materials as
well. However, the influences of crystal structure/
shape on the luminescent properties are less
reported.
dodecyl sulfonate (SDS), 8 mmol ZnCl2 and
0.24 mmol MnCl ꢀ 4H O were dissolved in a
2
2
mixture of 5 ml distilled water and 20 ml absolute
ethanol in a beaker. Then the solution was
dropped into 20 ml ethylenediamine under stirring
in a Teflon liner of 60 ml capacity. After about
10 min, the aqueous solution of 4 mmol Na2-
SiO ꢀ 9H O dissolved in 5 ml distilled water was
3
2
slowly added. The liner was sealed in a stainless-
steel autoclave, first aged at 90 1C for 12 h, and
then maintained at 220 1C for 6 days. After
quenched with water to room temperature quickly,
the resulting white solid products (sample c) were
filtered off, washed with distilled water and
absolute ethanol for several times, respectively,
and finally dried in vacuum at 60 1C for 4 h. For
comparison, one experiment (sample b) was
carried out through a procedure which was similar
to the above procedure except of the autoclave
cooled to room temperature in air; another
experiment (sample a) without SDS and air
cooling to room temperature was processed under
similar conditions.
Over the last decade, luminescent properties of
inorganic phosphors have been extensively inves-
tigated to make flat panel displays more commer-
cially available [9,10]. It is highly desirable to
develop novel low-voltage phosphors with high
efficiency and chemical stability under electron
beam bombardment in a high-vacuum system for
next generation field emission displays [11,12].
Mn-doped Zn SiO is a well-known phosphor for
2
4
its high luminescent efficiency and chemical
stability, and has been used as a luminescent
material for lamp and cathode ray tubes [13].
Many methods have been used to synthesize
Mn-doped Zn SiO phosphors [14–19]. But, few
The phase purity and phase structure of as-
prepared samples were characterized by the X-ray
powder diffraction (XRD) patterns, using a
Philips X’pert X-ray diffractometer equipped with
graphite monochromatized Cu Ka radiation
2
4
works reported the synthesis of 1D Mn-doped
Zn SiO and investigated the relationship between
2
4
shape/crystal structure and photoluminescence
properties.
Herein, we synthesized Mn-doped Zn SiO4
˚
(l ¼ 1:54178 A). The transmission electron micro-
scopy (TEM) images and corresponding selected
area electron diffraction (SAED) patterns were
performed with a Hitachi H-800 transmission
electron microscope using an accelerating voltage
of 200 kV. Photoluminescence (PL) spectra were
recorded on a Hitachi 850 fluorescence spectro-
meter with an Xe lamp at room temperature.
2
phosphor with different shape/crystal structure
via a low-temperature hydrothermal route without
further calcining treatment. The effects of crystal
structure or shape on the PL properties were also
2
+
investigated. The as-synthesized Zn SiO :Mn
2
4
phosphors are green or yellow luminescence
depending on the process conditions. This phe-
nomenon comes of the different crystal structures
of Zn SiO . The shape change of phosphors has a
3. Results and discussion
2
4
certain extent influence on their luminescent
intensity.
Fig. 1 shows emission spectra for green and
yellow luminescence at room temperature. The
green luminescence is the conventional green of
2
+
2
. Experimental section
Zn SiO :Mn
5
phosphor, occurring at about
25 nm. The yellow luminescence main peak
2
4
All reagents were purchased from Shanghai
Chemical Reagent Co. and used without further
purification. In a typical procedure, 1 g sodium
centers at 575 nm and there is still a weak peak
at 525 nm (Fig. 1c). To compare the intensity of
photoluminescence, it can be seen that the high PL

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34
J. Wan et al. / Journal of Luminescence 121 (2006) 32–38
(
b)
(b)
c)
a)
(
c)
(
(
a)
(
400
450
500
550
600
650
700
Wavelength (nm)
2
00
225
250
275
300
325
350
2 4
Fig. 1. Emission spectra of the Mn-doped Zn SiO phosphors
prepared in different conditions: (a) sample a—no SDS and
cooled in air; (b) sample b—added SDS and cooled in air; (c)
sample c—added SDS and quenched with water.
Wavelength (nm)
2 4
Fig. 2. Excitation spectra of the Mn-doped Zn SiO phosphors
prepared in different conditions: (a) sample a—no SDS and
cooled in air; (b) sample b—added SDS and cooled in air; (c)
sample c—added SDS and quenched with water.
intensity was obtained while surfactant SDS was
added. The green and yellow photoluminescence
come from the Mn impurities in the zinc silicate
higher energy is necessary to excite yellow emis-
sion. This result is in accordance with that of
emission spectra. To compare the intensity of
excitation spectra, it is found that there is an
analogous intensity relation with that of emission
spectra.
4
6
host material, and corresponding to the T - A
1
2
1
+
transition [20]. The luminescence of the Mn ion
is known to change depending on the host crystal
field, covering a wide range from blue–green to
red. Increasing the crystal field reduces the energy
difference of the ground and first excited state,
resulting in red-shift of the luminescence [21]. The
appearance of yellow luminescence is basically an
effect of the higher crystal field.
Fig. 3 shows the XRD patterns of the Mn-
doped Zn SiO phosphors synthesized at different
2
4
conditions. Sample a (no SDS and cooled in air)
and sample b (added SDS and cooled in air) can be
indexed to a same phase. All the diffraction peaks
of the as-synthesized samples can be indexed to a
pure hexagonal structured Zn SiO (a-phase) with
The excitation spectra for green and yellow
luminescence at room temperature are provided in
Fig. 2. From the excitation spectra, it can be seen
that they are almost similar. There is an excitation
band appearing at wavelengths shorter than
2
4
˚
˚
cell constants of a ¼ 13:92 A, and c ¼ 9:34 A,
which are in good agreement with the values in
the literature (JCPDS card no. 37-1485, a ¼
3
00 nm. This indicates that the luminescence for
green and yellow emission results from a same
˚
˚
13:93 A, and c ¼ 9:31 A). No obvious impurity
phase can be detected. Pattern c (added SDS and
quenched with water) represents a totally different
phase and has an approximate correspondence
with the b-phase of Zn SiO (JCPDS card no. 19-
2
+
source, i.e. Mn
ions. However, the peak
maximum of excitation spectrum for yellow
luminescence is blue shift compared to the green
2
+
one. This implies that Mn ions in yellow
emitting sample feel a stronger crystal field, so
2
4
1479). Several weak peaks in pattern c can be

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J. Wan et al. / Journal of Luminescence 121 (2006) 32–38
35
[23]. According to the above-mentioned opinion,
the appearance of yellow luminescence is attrib-
*
2
a-Zn SiO4
#
#
*
#
# β-Zn SiO4
#
#
2
#
uted to the higher crystal field in the b-Zn SiO
2
4
#
(
#
c)
*
#
#
*
#
*
#
#
# ###
#
host.
*
##
*
*
*
*
*
*
To investigate the difference of intensity of
photoluminescence in Fig. 1, the TEM images and
corresponding SAED patterns were performed.
Fig. 4 shows the images of the as-synthesized
samples in different conditions. The micrographs
of the as-synthesized sample a (no SDS and cooled
in air) are shown in Figs. 4a–c. From the TEM
*
*
*
*
*
(b)
*
*
*
*
*
*
*
* *
* * *
*
*
*
*
*
*
*
*
(a)
*
*
(Fig. 4a) image it can be seen that the as-
synthesized product is mainly composed of uni-
form rice-like particles with the average diameter
of 150 nm and length of 300 nm. In fact, the rice-
like nanoparticles consist of fine-sized nanorods.
This is clearly revealed by magnified TEM images
of a nanoparticle shown in Fig. 4b. The SAED
pattern (Fig. 4c) obtained from this nanoparti-
cle has a distortion dotted lattice, which reveals
the crystalline nature of Mn-doped Zn SiO
2
0
30
40
50
60
70
2θ (deg.)
Fig. 3. XRD patterns for samples synthesized at different
conditions: (a) sample a—no SDS and cooled in air; (b) sample
b—added SDS and cooled in air; (c) sample c—added SDS and
quenched with water.
2
4
index to a-phase of Zn SiO . b-Zn SiO is a
nanoparticles.
2
4
2
4
metastable phase, which occurs under certain
processing conditions. For instance, melting and
rapid cooling of near eutectic compositions of SiO2
and ZnO results in the formation of b-phase [22].
At room temperature, b-Zn SiO is quite stable,
Surfactant SDS plays a crucial role to obtain
zinc silicate nanorods. It is clearly revealed by the
TEM images shown in Fig. 4. In reactions b and c
(see Figs. 4d and g), Zn SiO nanorods can always
2
4
be obtained if SDS is added. Fig. 4d shows a
typical TEM image of the as-prepared Zn SiO
2
4
and only at high temperature does it transform to
a-phase. In our procedure, water quenching is
necessary to obtain b-Zn SiO . Because the cool-
2
4
nanorods with the average diameter of 80 nm and
length of several microns. Fig. 4e shows a
representative Zn SiO nanorod with high magni-
2
4
ing rate is still not enough, there are several weak
peaks of a-Zn SiO remained is in XRD pattern.
2
4
fication. The SAED pattern (Fig. 4f) obtained
from this individual nanorod has a highly symme-
trical dotted lattice, which reveals the single-
crystalline nature and further confirms the a-phase
crystal structure of rod-like Zn SiO . Compared
2
4
Compared to the XRD patterns, it is found that
sample b (added SDS and cooled in air) and c
(
added SDS and quenched with water) have higher
XRD diffraction intensity and sharper XRD peaks
than that of sample a (no SDS and cooled in air).
The intensification of XRD peaks would result in
improved luminescent intensity due to the increase
of crystallinity. This conclusion that samples b and
c have higher photoluminescent intensity than
sample a was easily obtained from the emission
and excitation spectra.
2
4
with sample b, nanorods of sample c have wide
size distribution covering from 80 to 300 nm
in diameter and several microns in length
(Figs. 4g–h). This phenomenon may result from
the inadequate Ostwald ripening growth process
due to the quick cooling rate. The SAED pattern
(Fig. 4i) obtained from a nanorod has a highly
symmetrical dotted lattice, which demonstrates
the single-crystalline nature and can be indexed
to b-phase crystal structure of Zn SiO nano-
The results of XRD can well explain the PL
peaks at different positions shown in Fig. 1. Green
luminescence centering at 525 nm corresponds to
the a-phase Zn SiO , while yellow luminescence
2
4
rods. These results of SAED are in accord with
that of XRD and further confirm the different
2
4
occurring at 575 nm comes from the b-Zn SiO4
2

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J. Wan et al. / Journal of Luminescence 121 (2006) 32–38
Fig. 4. Representative TEM image and the SAED pattern of synthesized samples at different conditions: (a–c) sample a—no SDS and
cooled in air; (d–f) sample b—added SDS and cooled in air; (g–i) sample c—added SDS and quenched with water.

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J. Wan et al. / Journal of Luminescence 121 (2006) 32–38
37
luminescence come from different crystal structure
of Zn SiO .
characterized to the formation of a-phase zinc
silicate nanoparticles and nanorods, that show
green luminescence centering at 525 nm, and the
other one is characterized as b-phase nanorods,
showing yellow luminescence occurring at 575 nm.
The as-synthesized Zn SiO nanorods in the
2
4
Combining Fig. 1 with Fig. 4, it can be
concluded that Zn SiO nanorods have higher
PL intensity than Zn SiO nanoparticles. It is well
2
4
2
4
known that nanosized materials have large surface
area. The large surface area has the serious
drawback in PL intensity due to the introduction
of a large number of defects into the phosphor
crystal. Defects have serious implications for
luminescence materials as they provide non-
radiative recombination routes for electrons and
holes. In order for the material to be as efficient as
possible, the number of electron/hole recombina-
tions via optically active centers must be max-
imized. Therefore, the crystalline crystal is as
important as the choice of host materials and the
light-emitting center. If the host materials have
high crystalline and little surface area, the propor-
tion of surface-damaged region to undamaged
bulk decreases. Higher PL intensity can be
obtained as a result of the improved crystal quality
2
4
presence of surfactant SDS have higher PL
intensity than Zn SiO nanoparticles prepared in
2
4
the absence of SDS. It is attributed to the low
surface area and high crystallinity of Zn SiO
2
4
nanorods. Furthermore, this article provides a
simple route to obtain Mn-doped Zn SiO phos-
2
4
phors with different luminescence and PL inten-
sity. The results may provide helpful guidance for
the application of Mn-doped Zn SiO phosphors.
2
4
Acknowledgements
This work is supported by the National Natural
Science Foundation of China and the 973 Project
of China.
[
24]. Annealing treatment is an effective way to
improve the emission intensities of phosphor due
to low surface defects and improved crystallinity
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