APPLIED PHYSICS LETTERS 89, 043112 ͑2006͒
a͒,b͒
Runping Jia, Guoxin Zhang, and Qingsheng Wu
Department of Chemistry, Tongji University, Shanghai 200092, People’s Republic of China
a͒,c͒
Yaping Ding
Department of Chemistry, Shanghai University, Shanghai 200444, People’s Republic of China
͑
Received 7 March 2006; accepted 3 June 2006; published online 27 July 2006͒
AWO ͑A=Ca,Sr,Ba͒ nanofilms are prepared by a self-inventive technique using collodion to
4
disperse nanoparticles and form film, and their photoluminescence ͑PL͒ properties are controlled by
a nano-TiO2 doping method. This cannot only reach the results of uniform film and PL
enhancement, but also realize a PL increase/decrease shift effect. The PL behaviors of AWO4
nanofilms doped by TiO are in good agreement with Gaussion function relation. In addition, there
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is a positive correlation between the critical concentrations of TiO in AWO –TiO nanofilm series
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Scheelite-type tungstates are important luminescent
diffraction peaks at ͑101͒ and ͑200͒ increase while that of
͑004͒ decrease when doping. This may also result from W
replacement by Ti. Moreover, it is noticed that a diffraction
peak appears at 25° ͑2͒ in only CaWO –TiO system ͓Fig.
1
,2
materials, whereas their more extensive applications are
3
4
often limited. Thus several processes including doping,
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6
nanofabrication, and film formation are proposed to im-
prove their optical properties. However, few studies on tung-
state nanofilms have been reported;
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2
1
͑a3͔͒. Initially, we think that it is the diffraction of TiO2.
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–9
in particular, their
However, almost all of the other XRD results do not support
it, whether seen from the other diffraction peaks of
CaWO –TiO or from the XRD patterns of SrWO –TiO
photoluminescence ͑PL͒ control are scarcely investigated.
Herein a technique of nanoparticle dispersal and film forma-
tion through collodion is proposed to prepare AWO4 ͑A
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2
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2
and BaWO –TiO .
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2
=
Ca,Sr,Ba͒ nanofilms; a nano-TiO doping route is devel-
2
Fourier transform infrared ͑FTIR͒ spectra prove the
oped to control their PL performance. The approaches cannot
only reach the results of uniform film and PL enhancement,
but also realize a PL increase/decrease shift effect. This will
lay a foundation for nanophotoelectron devices.
presence of AWO ͑A=Ca,Ba,Sr͒ in nanofilms by the char-
4
−1
acteristic bands in the region of 770–890 cm .
Scanning electron microscopy ͑SEM͒ images ͑Fig. 2͒
show that all of the nanofilms possess homogeneous surface
AWO ͑A=Ca,Sr,Ba͒ and TiO nanoparticles are syn-
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2
morphology and are crack-free. AWO nanofilms exhibit a
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thesized in the light of Ref. 10 and 11, respectively. The two
kinds of nanoparticles at a proper ratio are dispersed into the
mixture solution containing absolute ethanol and collodion
relatively low roughness without obvious granular structure.
However, when TiO nanoparticles about 30 nm are intro-
2
duced, the roughness of AWO nanofilm increased remark-
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͑
10:1͒. Then they are uniformly coated on a clean glass slide
by dip-pulling method. The films are heated at a rate of
°C/min and kept at 200 °C for 30 min, at 500 °C for 1 h
ജ550°C, TiO transform from Anatase to Rutile͒, orderly,
ably. Moreover, AWO4 ͑A=Ca,Sr,Ba͒ nanoparticles are
spherelike ͑ϳ100 nm͒, claylike ͑ϳ100 nm͒, and spindlelike
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͑
͑
length: ϳ180 nm, diameter: ϳ50 nm͒, respectively. Each of
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them together with TiO nanoparticles forms quality-well
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then annealed. AWO bulk crystals are obtained by directly
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composite nanofilm.
Seen from PL spectra ͑Fig. 3͒, the emission peaks of
AWO4 ͑A=Ca,Sr,Ba͒ nanofilms are at 412, 395, and
mixing isovolumetric 0.4M of ACl and Na WO solutions.
2
2
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X-ray diffraction ͑XRD͒ analysis shows that TiO nano-
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particles are anatase phase with a tetragonal structure. Broad-
ened diffraction peaks are also observed, which can be attrib-
uted to the small domain size and poor crystallinity ͓Fig.
3
90 nm, respectively, and those of AWO –TiO composite
4 2
nanofilms are at the same position, although that of TiO2
nanofilms is at 363 nm. However, nanofilm fabrication and
nanofabrication bring about the PL shift, in which the emis-
sion peaks are all blueshifted compared with those the bulk
crystals, but the effect of the former is more than that of the
latter ͑338, 350, 334 nm͒. These are the behaviors of quan-
tum size effect. On the other side, the emission peak inten-
sities of AWO nanofilms are obviously varied by TiO dop-
1
͑d͔͒. AWO nanofilms and their composite films are all te-
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tragonal scheelite-type structure ͓Figs. 1͑a͒–1͑c͔͒. This indi-
cates that the structure and framework of tungstate are not
affected by both sinter and doping. AWO –TiO composite
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2
nanofilms are composed of both well-crystalline AWO and
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ultrafine poor crystallized TiO . The cell parameters of
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AWO ͑A=Ca,Sr,Ba͒–TiO composite films are a=5.2812,
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2
4
2
ing, but AWO nanoparticle systems are not influenced even
c=12.0758; a=5.4758, c=12.9069; and a=5.613,
c
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after heat treatment. However, the emission peak positions of
=
12.8750, respectively. All of them are a little larger than
those in corresponding JCPDS cards, which may be a result
of W replacement by Ti. Additionally, we discover that the
both AWO nanoparticles and nanofilms are hardly changed
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by doping TiO2. In particular, the PL intensities not only can
be enhanced with the increase of TiO in certain ranges, but
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a͒
also can increase/decrease around the critical concentration
Authors to whom correspondence should be addressed.
Electronic mail: qswu@mail.tongji.edu.cn
b͒
of TiO ; that is, the PL increases/decreases shift effect.
2
c͒
Electronic mail: wdingyp@sina.com
Therefore, Gaussian fitting technique is used to investigate
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Jia, Runping
