Chapter3
Structural and optical characterization of
CdSe and CdSe/Tb3+/Sm3+doped
titania-zirconia hosts
Cadmium
selenide
semiconductor
nanocrystals
along
with
samarium ions and terbium ions were incorporated in titaniazirconia hosts through sol-gel route. Thermal stability of the matrix
was analysed by thermogravimetric studies.The FT-IR spectrum
reveals the different vibrational modes present in the sample. The
electron diffraction and TEM measurements have yielded the values
of crystal plane spacing and the crystallite size. The average size of
nanocrystals was determined to be 10.8 nm. The absorption spectrum
confirms the formation of cadmium selenide nanoparticles. Raman
analysis also reveals the formation of CdSe nanoparticles. The
fluorescence intensities were compared for Tb3+ and Tb3+/CdSe doped
TiO2–ZrO2 matrices. Further, the fluorescence intensities were also
compared for Sm3+ and Sm3+/CdSe doped titania–zirconia matrices.
The fluorescence intensities of the terbium ions and samarium ions
were found to be greatly enhanced by codoping with CdSe
nanoparticles.
Chapter 3
3.1 Introduction
Sol–gel synthesis is a low-temperature method. It is used for
preparing optically transparent amorphous materials, in which the
inclusion of metallic, inorganic and organic additives is readily
accomplished. Optical qualities and optimal structure may be
achieved by controlling thermal and atmospheric processing when
the gel dries and densifies [1]. Sol-gel chemistry offers a possibility
for the ambient preparation of important optical materials like
xerogels or layers doped with rare earth ions. Optically active
elements like rare earths and nanocrystals can be incorporated as
dopants into a sol–gel matrix. The sol–gel glasses can hold a higher
concentration of dopants than traditional melt glasses without losing
their amorphous character [2].
Mixed zirconium and titanium oxides bring forth new
reactivity properties and enhanced activity due to structural and
electronic modifications induced by the dopant. These oxides show
good intrinsic properties through their specific surface area and
thermal stability. Metal oxides like titania and zirconia, are very
useful because of their stability in aqueous environment in a large
pH window [3–5]. TiO2–ZrO2 composites have tunable composition,
abundant phases and more attractive photocatalytic properties than
pure TiO2. Various methods are used to synthesise TiO2–ZrO2
composites with different morphologies [6–8].
93
Structural and optical characterization of CdSe ….
Rare earth ions doped glasses have wide variety of
applications [9, 10]. Due to the good fluorescence efficiency in the
visible and infrared region, the spectroscopic studies of trivalent
samarium ions have attracted much attention [11]. The luminescence
properties of Sm3+ ions is of great importance due to its potential
applications in solar cells, night vision cameras etc. [12]. Among
different rare earth ions, terbium ions have absorption and emission
in the visible range and its sharp green fluorescence can be used for
display applications. Many studies have been carried out on the
preparation and luminescence properties of Tb3+ and other rare-earth
complexes in sol–gel derived silica matrix [13-15]. Tb3+-doped glasses
and glass fibers have been used in non-destructive testing [16] and
high-resolution medical X-ray imaging field such as mammography
[17].For the Tb3+-doped glass materials used in medical applications,
the light yield is the most important parameter, because it can reduce
the radiative dose exposed to patients [18]. This material could be
used as phosphors for fluorescent lamp and emission agents or
sensitizing agent for plasma displays. The Tb3+doped phosphor films
are more environment friendly and energy efficient than mercurycontaining fluorescent lamps.
In the field of materials for optical applications, an increased
interest has been shown lately to a special class of composite
materials: semiconductor doped glasses [19,20]. Semiconductor
doped glasses can be used for the fabrication of integrated optical
94
Chapter 3
structures, optical circuits with fast switching time, planar channel
wave guides, optical modulators, electro-optical switches etc.[21-23].
The greatest disadvantage of this composite material is the relatively
low efficiency of the optical nonlinear phenomena compared with
those in bulk semiconductors. Semiconductor nanoparticles show
unique size-dependent optical properties and these characteristics
open new applications, including biotechnology and electronics [24,
25]. Nanomaterials in the form of nanoparticles or bulk nanocrystals
show attractive luminescence properties. Due to quantum size effect,
the physical properties of semiconductors and nanoparticles are
different from those of bulk. So these materials are attractive and
different methods have been employed to synthesis them [26, 27].
The interactions between nanoparticles and surrounding
environments play essential roles in the optical responses of
semiconductor nanoparticles. Rare earth ions/semiconductors doped
gels and glasses have attracted much attention due to high quantum
efficiencies, energy transfer processes and luminescence properties
[28].Quantum dots play the roles of both the formation of tunneling
channel and the enhancement of the light conversion efficiency in the
visible spectral range. Most research has been done on silicate [2930], borosilicate [31-32] and alumino-phosphate [33-36] glass matrices
containing semiconductor nanocrystallites like CdS and CdSe. In this
chapter, we present the preparation and characterization ofTiO2-ZrO2
95
Structural and optical characterization of CdSe ….
matrices doped with CdSe nanocrystallites along with samarium and
terbium ions. The fluorescence intensities were compared for Tb3+
and Tb3+/CdSe doped samples. Similarly, the fluorescence intensities
were also compared for Sm3+ and Sm3+/CdSe doped samples. The
fluorescence enhancement of samarium and terbium ions in the
presence of CdSe nanocrystallites is also reported.
3.2 Experimental:
TiO2-ZrO2 gels containing CdSe/Sm3+ and CdSe/Tb3+ were
prepared by sol-gel process with titanium iso propoxide and
zirconium IV propoxide as precursors in the presence of ethanol as
solvent. The dopants were added in the form of cadmium acetate,
selenic acid,samarium nitrate and terbium nitrate. Cadmium acetate
and selenic acid were used as cadmium and selenium sources,
respectively. A measured volume of 1M HNO3was added as catalyst.
Three samples were prepared with the following composition
Sample ATiO2-ZrO2 -75:25 + CdSe(3 Wt %)
Sample BTiO2-ZrO2 -75:25 + Tb3+(3 Wt %) + CdSe(3 Wt %)
Sample C TiO2-ZrO2 -75:25 + Sm3+ (3 Wt %) + CdSe (3 Wt %)
The resulting mixture was stirred continuously using a
magnetic stirrer for about an hour at room temperature till it formed
a uniform clear solution. The mixture (sol) is poured into
polypropylene containers, which is sealed and kept for one month to
96
Chapter 3
form stiff gels.. The samples were clear, transparent and colourless.
Finally the three samples were annealed at 55000C for two hours. The
colour of the matrix turned into brown.
brown A photograph of the CdSe
doped sample is shown in Figure
igure 3.1.
3
Figure 3.1: Photograph
hotograph of CdSe doped TiO2-ZrO2 matrix
The FT-IR
IR spectra of the glasses were
we recorded using Perkin Elmer
Spectrum 400 fluorescence spectrometer Shimadzu in the range 4004000
cm-1with
a
spectral
resolution
of
11cm-1.
Thermo
gravimetric/differential
differential thermal
therma analysis of the samples were done
by using Shimadzu DTG 60 system. The values were acquired at a
heating rate of 10C/min. The excitation
e
and emission spectra were
taken using spectrophotofluorimeter (Shimadzu-RFPC
(Shimadzu
5301) and the
absorption
spectra
were
measured
with
UV-Visible
spectrophotometer (Shimadzu-UVPC
(Shimadzu
2401) for the samples annealed
at 5000C. The particlee size was
wa measured with Tecnai G2 30 S-Twin
transmission electron microscope (TEM) at 300 kV. Micro- Raman
spectra of the samples were
we
recorded using Labram-HR 800
spectrometer equipped with excitation source laser radiation at a
97
Structural and optical characterization of CdSe ….
wavelength of 514 nm from an Argon-Iron laser. Spectra were
received by 1800 greeds/mm grating, a super- notch filter having a
cut off at 50 cm-1 and Peltier cooled CCD camera, allowing a spectral
resolution of about 1cm-1.
3.3 Results and discussion
3.3.1Structural and optical characterizations of CdSe doped titaniazirconia matrix
3.3.1.1 TEM analysis
The HRTEM and SAED pattern of CdSe nanocrystals
annealed at 5000C is shown in Figure 3.2(a) and (b), respectively.
Figure 3.2(a) gives the planes of the CdSe nanocrystallites.
Figure 3.2: (a) HRTEM micrograph and (b) Selected area electron
diffraction pattern of CdSe nanocrystals doped TiO2-ZrO2 matrixannealed
at 5000C
98
Chapter 3
The d values obtained from the HRTEM micrograph are found to be
consistent with the d values of bulk CdSe crystal (ICDD no: 19-0191).
From HRTEM, the plane distances (d) are found to be 3.58 Å,2.12
Å,1.82Å ,1.52Å,1.38Å, 1.23Å, 1.18 Å, 1.06 Å, which match the (111),
(220), (311), (400), (331),(422), (511) and (440) planes of bulk CdSe
having d values 3.511Å, 2.149 Å, 1.833 Å, 1.519 Å, 1.394 Å, 1.240 Å,
1.169 Å and 1.075Å,respectively. The average size of nanocrystals is
determined to be 10.8 nm. The rings on the SAED image (Figure
3.2(b)) indicate the polycrystalline nature of CdSe nanocrystals.
.3.3.1.2 Raman analysis
Raman spectrum of CdSe doped titania-zirconia matrix is
shown in Figure 3.3.
1400
150
Sample A
CdSe 3%
Intensity(arb.unit)
1200
1000
205
800
600
393
400
515
638
200
0
200
400
600
800
1000
-1
Raman Shift (cm )
Figure 3.3: Raman spectrum of CdSe dopedTiO2-ZrO2 matrix
99
Structural and optical characterization of CdSe ….
The bands at 150, 205, 393, 515 and 638 cm-1 are observed in the
spectrum. The bands obtained around at 150 cm-1 and 515 cm-1
indicate the presence of hydrous zirconium titanate, which shows the
bonding Zr-O-Ti. The band at 393 cm-1 corresponds to crystalline
anatase titania. The band at 638 cm-1 corresponds to monoclinic
zirconia[37]. For CdSe nanocrystals the LO phonon frequency is
observed at ωLO= 205 cm–1 and for bulk CdSe crystals, it is at ωLO= 212
cm–1 [38]. Thus, we see a noticeable decrease in the frequency of LO
phonon due to their spatial confinement. Also in CdSe nanocrystals
the 2 LO phonon frequency is obtained at 405 cm–1. Usually this peak
is narrow. Thus Raman band at 205 cm-1clearly reveals the presence
of CdSe nanocrystals.It is also possible that Raman bands may vary
with sintering time, indicating slight differences in structural order.
From the Raman analysis, it can be noticed that this technique is
more sensitive to short range order than X-ray diffraction. It can
show the intermediate crystallization of anatase or rutile as well as
monoclinic zirconia. The position of the active Raman modes depend
on lattice vibration of the sample and the effect is more significant for
reduced size materials.
3.3.1.3TGA/DTA analysis
Thermo gravimetric/differential thermal analysis (TGA/DTA)
curves (temperature range 30-10000C) of the CdSe doped titaniazirconia matrix are shown in Figure 3.4.
100
Chapter 3
Figure 3.4: TGA/DTA curves of the CdSe
doped TiO2-ZrO2 matrix
An endothermic peak is observed in the DTA curve at 1000C. The
TGA curve shows a 12% weight loss around this temperature range.
A broad exothermic band is observed in the DTA curve at 2300C. The
second stage of weight loss also appears in the TGA curve at this
temperature. The curve shows 11% weight loss around this
temperature range. A total weight loss of about 30% is observed
when heating up to 10000C. It could be attributed to the dissociation
of various bonds arises due to free water, loosely held hydroxyl
groups, weak organic compounds, different forms of alcohol, etc.
101
Structural and optical characterization of CdSe ….
3.3.1.4 FTIR studies
The FTIR spectrum of the CdSe doped TiO2-ZrO2 sample is
Transmittance(arb.unit)
210
Transmittance (arb. unit)
shown in Figure 3.5.
CdSe (3%)
180
150
128
127
126
125
124
123
663 cm-1 Zr-O-Ti bond
122
121
120
640
650 660 670 680
Wavenumber (cm-1)
440 cm-1
120
690
700
Sample A
841 cm-1
90
400
500
600
700
800
900
1000
-1
Wavenumber(cm )
Figure 3.5: FT-IR spectrum of CdSe doped TiO2-ZrO2 matrix
The spectrum exhibits strong band at 440 cm-1, indicating the
presence of Ti-O-Ti bond. The band at 663 cm-1 is related to Zr-O-Ti
vibrations [37]. The band at 841 cm-1 indicates Zr-O-Zr bond.
3.3.1.5 Absorption studies
The optical absorption spectrum of TiO2-ZrO2 matrix doped
with CdSe nanocrystallites annealed at 5000C is shown in Figure 3.6.
102
Chapter 3
1.0
Sample A
Absorbance(arb.unit)
0.8
CdSe ( 3%)
0.6
0.4
0.2
0.0
300
400
500
600
700
Wavelength(nm)
Figure 3.6: Absorption spectrum of CdSe doped TiO2-ZrO2 matrix
The direct absorption band gap of the CdSe nanoparticles can be
determined by fitting the absorption data to the tauc equation
α h ν = B (h ν − E g )1 / 2
(3.1)
in which hνis the photon energy, α is the absorption coefficient, Eg is
the absorption band gap and B is a constant relative to the material.
The absorption coefficient can be obtained using the equation.
α=
2.303 A
d
(3.2)
where A is the absorbance and d is the thickness of the sample. The
plot of α2 versus hν is shown in Figure 3.7.
103
Structural and optical characterization of CdSe ….
6
1.4x10
CdSe 3%
6
1.2x10
6
Eg = 3.17 eV
2
-2
α ( cm )
1.0x10
5
8.0x10
5
6.0x10
5
4.0x10
5
2.0x10
0.0
2.0
2.5
3.0
3.5
4.0
hυ(eV)
Figure 3.7:α2 vs hν
ν graph for the determination of optical band gap of the
CdSe doped TiO2-ZrO2 matrix
The plot of α2 versus hνgives the value of the band gap as
3.17 eV. This is large compared to the bulk CdSe, a direct
semiconductor with band gap energy of 1.7eV [38]. Semiconductor
nanocrystals are known to have an absorption edge, which is shifted
with respect to the bulk material, towards shorter wavelength
[39].The blue shift of the absorption edge can be explained by the
effective mass approximation model, developed by Brus [40] and
Kayanuma [41]. In the strong exciton confinement regime of
nanoparticles (particle radius<ab*), the energy E(R) for the lowest 1S
excited state as a function of cluster radius (R) given by
E ( R) = E g +
πeab * 1.786e 2
−
+ 2.48ER
8εR 2
4πεR
104
(3.3)
Chapter 3
where ab* is the Bohr radius of the exciton (for CdSe, ab*=5.6 nm), ߝ is
the dielectric constant of the nanocrystallite (for CdSe, ߝ = 8.98) and
ER is the bulk exciton Rydberg energy (for CdSe, ER= 0.016eV). The
first term in equation (3.3) is the band gap energy for bulk material
and it is 1.7 eV for CdSe. The second term is the quantum
confinement localization for the electrons and holes, which leads to
the blue shift. The third term is the coulomb term leading to red shift,
while the fourth term gives the spatial correlation energy, which is
small and of minor importance. The band edge absorption is used to
calculate the average size distribution of the CdSe nanoparticles in
the titania-zirconia matrix. The particle radius is estimated to be 4.5
nm using the absorption spectrum and the Brus formula. The
calculated size is found to be 9 nm of diameter.
3.3.2
Optical characterizations of CdSe /Tb3+ doped titania-
zirconia matrix
Optical absorption spectra of Tb3+and Tb3+/CdSedoped TiO2ZrO2 matrices annealed up to 5000C are shown in Figure 3.8.
105
Structural and optical characterization of CdSe ….
Tb3% CdSe3%
Tb3%
Absorbance (arb.unit)
1.0
0.8
7F ->5G
6
4
0.6
7F ->5L
6
10
0.4
0.2
0.0
320
340
360
380
400
420
Wavelength (nm)
Figure 3.8:Absorption spectra of Tb3+and Tb3+/CdSe
doped TiO2-ZrO2 matrices
The absorption spectra show two absorption bands corresponding to
the transitions like 7F6→5G4 (352 nm) and 7F6→5L10 (368nm). Figure 3.9
presents the fluorescence spectra of the samples annealed up to
5000C with an excitation wavelength of 368 nm.
300
250
5
7
D4-> F5
Tb3% CdSe3%
Tb3%
Intensity (arb.unit)
200
150
5
7
D4-> F4
100
5
7
D4-> F3
50
0
500
550
600
650
Wavelength (nm)
Figure 3.9: Emission spectra of Tb3+ and Tb3+/CdSe
doped TiO2-ZrO2 matrices
106
Chapter 3
The emission spectrum of Tb3+ consists of three bands located at 542
(green), 583 (yellow) and 618 nm (red), corresponding to
transitions5D4→7F5, 5D4→7F4 and5D4→7F3, respectively. Among them,
the green emission at 542 nm related to the transition 5D4→7F5 is the
strongest. The typical luminescence of Tb3+ appears to be green to the
human eye, because the emission due to the 5D4→7F5 transition
usually dominates overall emissions. The fluorescence intensity of
CdSe/Tb3+ doped sample is found to be 12 times stronger than that of
Tb3+ alone doped sample.
The structural features play a critical role on the fluorescence
enhancement, since the complex dielectric function of the composite
medium depends directly on the structural features of the particles
involved. The heat treated sample provides an increase in the
number of non-bridging oxygen (NBO) atoms, which in turn
increases the phonon density around the Tb3+ ions. Also due to the
shrinkage of the sample by heat treatment, there is a possibility of
clustering of ions which paves the way for the proximity of CdSe
nanocrystallites to the Tb3+ ions. These structural features favour the
phonon assisted nonradiative energy transfer from CdSe to Tb3+ ions.
Thermal treatment allows to improve the crystalline quality of the
clusters and characteristic optical features [42].
107
Structural and optical characterization of CdSe ….
Figure 3.10: Energy transfer mechanism for CdSe-Tb3+ system
As a result of finite size, continuous bands of energy are
replaced by molecule like discrete energy levels. As the particle size
increases the energy spacing between the states decreases. In
nanoparticles, most ions at the surface are non-saturated in
coordination. Electrons and holes may be easily excited and escape
from the ion. Much more carriers trapped at the surface states or
defect sites are released by photoexcitation as excitonic or trapped
luminescence [43, 44]. The quantum confinement enhances the
allowed energies resulting from an increase in binding energy of
shallow impurity [45].
Heat treatment leads to an increase in the inhomogeneities of
the local environment owing to the cross linking between titaniazirconia chains and consequent shrinkage. As the densification
108
Chapter 3
continues, clustering of Tb3+ induces strong energy transfer even at
lower concentrations. From the fluorescence spectra (Figure 3.9) it is
observed that the fluorescence intensity of Tb3+ increased due to the
presence of CdSe nanoparticles. The energy transfer mechanism for
the CdSe-Tb3+ system is shown in Figure 3.10. Enhancement in
emission spectra can be attributed to the nonradiative energy transfer
from the electron-hole recombination of the CdSe nanoparticles to
the rare earth ion. Figure 3.11 shows the excitation spectra taken with
an emission wavelength of 542 nm for Tb3+ doped and Tb3+/CdSe
codoped samples. The excitation spectra are the true finger prints of
the characteristic absorption lines corresponding to 4f-5d transitions
of terbium ions. The figure show strong excitation bands with the
codoping of CdSe nanocrystallites.
0.18
Tb3%
Tb3% CdSe3%
0.16
7F ->5G
6
4
7F ->5L
6
10
Intensity(arb.unit)
0.14
0.12
0.10
0.08
0.06
0.04
340
350
360
370
380
390
400
Wavelength(nm)
Figure 3.11: Excitation spectra of Tb3+and Tb3+/CdSe
doped TiO2-ZrO2 matrices
109
Structural and optical characterization of CdSe ….
3.3.3
Optical characterizations of CdSe/Sm3+ doped titania-
zirconia matrix
Optical absorption spectra of Sm3+ and Sm3+/CdSe doped TiO2ZrO2 matrices annealed at 5000C are shown in Figure 3.12. The
ground state of the Sm3+ ion is 6H5/2 and the absorption bands arise
due to transitions from this level to various excited levels. The
absorption spectra show nine absorption bands corresponding to
transitions 1) 6H5/2→4H9/2 (344 nm), 2) →4D3/2 (362 nm) 3) →6P7/2 (375
nm), 4) →4L15/2 (391nm), 5) →6P3/2 (401 nm), 6) →6P5/2 (415 nm), 7)
→4G9/2 (440 nm) 8) →4I 13/2 (463 nm) and 9) →4I11/2 (478) nm.
0.165
0.160
Absorbance (arb.unit)
0.155
Sm3%
Sm3% CdSe3%
6
P3/2
6H ->
5/2
0.150
0.145
4H
9/2
4
0.135
4D 6P L15/2
3/2 7/2
0.140
4I
13/2
6P
5/2
4I
11/2
4G
9/2
0.130
0.125
0.120
0.115
0.110
340
360
380
400
420
440
460
480
Wavelength (nm)
Figure 3.12: Absorption spectra of Sm3+ and Sm3+/CdSe
doped TiO2-ZrO2 matrices
110
Chapter 3
200
4G ->6H
7/2
11/2
Sm3%
Sm3% CdSe3%
Intensity (arb.unit)
150
4G ->6H
7/2
9/2
100
4G ->6H
7/2
13/2
50
0
560
600
640
Wavelength (nm)
Figure 3.13: Emission spectra of Sm3+ and Sm3+/CdSe
doped TiO2-ZrO2 matrices
Emission spectra of Sm3+ and Sm3+/CdSe doped samples taken
at excitation wavelength 401 nm are shown in Figure 3.13. The
emission peak at 595nm corresponding to the transition 4G7/2 →6H11/2
is the most intense one. From the fluorescence spectra we observe
that the fluorescence intensity of Sm3+ increased due to the presence
of CdSe nanoparticles. The observed emission spectra are similar to
those of the other reported Sm3+ systems[46, 47].Improved efficient
luminescence was obtained in Sm3+/CdSe codoped titania-zirconia
due to the more dispersion of Sm3+ ions compared to Sm3+ single
doped samples. This clearly indicates that the presence of the
nanocrystallites is responsible for an increase of both the covalency
and the polarization of the local vicinities of the Sm3+cations.The
111
Structural and optical characterization of CdSe ….
intensity of fluorescence from Sm3+ in titania-zirconia matrix is highly
dependent on the preparation, drying procedure and also varies as a
function of time and temperature of dehydration of the gel. The
polycondensation of the gel, and its associated densification prevents
the oxidation of the crystallites.
The possible explanation is that CdSe nanoparticles doped in
the
network
of
TiO2-ZrO2:Sm3+
matrix
would
increase
the
concentration of Ti- Zr dangling and oxygen vacancy in the network
of the TiO2-ZrO2matrix [48]. In this way, more electrons or holes can
be easily excited and radiative recombinations can be increased. So
the emission intensity of the codoped sample markedly increased. By
exciting at 401 nm the energy from the nonradiative recombination of
electron-hole pairs of the CdSe nanoparticles can be transferred to
the higher energy levels of the Sm3+ ion. This will increase the
population of the emitting levels and thereby increasing the
fluorescence from the rare earth ions. The energy transfer mechanism
for the CdSe-Sm3+ system is shown in Figure 3.14. Here the
fluorescence intensity of CdSe/Sm3+ doped sample is 20 times
stronger than that of Sm3+ alone doped sample. The excitation spectra
of Sm3+ and Sm3+/CdSe doped samples are shown in Figure 3.15.
112
Chapter 3
Figure 3.14: Energy transfer mechanism for CdSe-Sm3+ system
400
Sm3%
Sm3% CdSe3%
6H ->
5/2
350
4
I13/2
Intensity (arb.unit)
300
4
I11/2
4
G9/2
250
6
P3/2
200
150
6
P5/2
4
L15/2
100
4
D3/2 6P
4
7/2
H9/2
50
0
320
360
400
440
480
Wavelength (nm)
Figure 3.15: Excitation spectra of Sm3+ and Sm3+/CdSe
doped TiO2-ZrO2 matrices
113
Structural and optical characterization of CdSe ….
The excitation spectra taken with an emission wavelength of 595 nm
show the different transitions associated with Sm3+ ions. The
intensity of the spectrum highly enhanced with the codoping of CdSe
nanocrystallites.
3.4 Conclusions:
Titania-zirconia
matrix
doped
with
CdSe/Tb3+
and
CdSe/Sm3+are prepared through sol-gel route. The absorption
spectrum confirms the formation of CdSe nanoparticles along with
terbium ions and samarium ions in the titania-zirconia matrix. The
average size of the nanoparticle estimated from the optical analysis
agreed well with that obtained from the TEM micrograph. The
average size of nanocrystals is determined to be 10.8 nm. The Raman
analysis also shows the formation of CdSe nanoparticles. Thermal
stability of the matrix was obtained by the thermogravimetric
analysis.The FT-IR studies shows the different vibrational modes
present in the CdSe doped titania-zirconia matrix.In Tb3+ doped
glasses, the 4f-5d transition would play an important role for the
emission of Tb3+. The green emission at 542 nm associated with the
transition 5D4→7F5 is the strongest. The fluorescence intensity of Tb3+
increased due to the presence of CdSe nanoparticles. The
fluorescence excitation spectra confirm the energy transfer from
CdSe nanoparticles to Tb3+ ions. The CdSe/Sm3+ doped sample the
emission peak at 595nm corresponding to the transition 4G7/2 →6H11/2
114
Chapter 3
is most intense one. From the fluorescence spectra the fluorescence
intensity of Sm3+ increased due to the presence of CdSe nanoparticles.
The excitation spectrum also shows strong excitation bands with the
codoping of CdSe nanocrystallites. Enhancement in emission spectra
can be attributed to the nonradiative energy transfer from the
electron-hole recombination of the CdSe nanoparticles to the rare
earth ions. This type of fluorescence enhancement is of particular
interest for potential applications such as phosphor materials for
light-emitting devices.
115
Structural and optical characterization of CdSe ….
References
[1]
C.J. Brinker, G.W. Scherer, Sol–Gel Science: The Physics and
Chemistry of Sol–Gel Processing, Academic Press(1990)Boston.
[2]
H.R. Li, H.J. Zhang, J. Lin, S.B. Wang,K.Y. Yang,J. Non-Cryst.
Solids278 (2000) 218.
[3]
T. Van Gestel, C. Vandecasteele, A. Buekenhoudt, C.
Dotremont, J. Luyten, R. Leysen, B. van de Bruggen, G. Maes, J.
Memb. Sci.207(2002) 73.
[4]
T.
Van
Gestel,
H.
Kruidhof,
D.H.A.
Blank,
H.J.M.
Bouwmeester,J. Memb. Sci. 284 (2006) 128.
[5]
R. Vacassy, C. Guizard, V. Thoroval, L. Cot,J. Memb. Sci. 132
(1997) 109.
[6]
M. Zorn, D.T. Tompkins, W.A. Zeltner, M.A. Anderson,
Environ. Sci. Technol. 34(2000) 5206.
[7]
S.W. Liu, Z.L. Xiu, J. Pan, X.P. Cui, W.N. Yu, J.X. Yu, J. Alloys
Compd. 437 (2007)L1.
[8]
R.A. Lucky, P.A. Charpentier, Adv. Mater. 20 (2008) 1755.
[9]
M.C. Kelvin,Phys. Rev. B42 (1990) 1123.
[10] E. Lifshitz, I. Dag, I. Litvin, G. Hodes, G. Gorer, R. Reisfeld, M.
Zelner, M. Minti,Chem. Phys. Lett. 288 (1998) 196.
[11] H. Linet al, Appl. Phys. Lett.80 (2002)2642.
[12] P.
Nemec,
J.
Jedelsky,
Solids326(2003)325.
116
M.
Frumar,
J.
Non-Cryst.
Chapter 3
[13] A.J. Silversmith, D.M. Boye, K.S. Brewer, C.E. Gillespie, Y.
Lu,D.L. Campbell,J. Lumin. 121 (2006) 14.
[14] C. Armellini, M. Ferrari, M. Montagna, G. Pucker, C.
Bernard,A. Monteil,J. Non-Cryst. Solids 245 (1999) 115.
[15] P.V. Jyothy, K.A. Amrutha, J. Gijo,N.V. Unnikrishnan
J.
Fluoresc. 19 (2009) 165.
[16] C. Bueno, R.A. Buchanan, Luminescent glass design for
highenergy real-time radiography, SPIE 1327 (1990) 79.
[17] W.P. Siegmund, P. Nass, J.P. Fabre, W. Flegel, V. Zacek, G.
Martellotti, G. Wilquet, Glasses as active and passive
components for scintillating fiber detectors, SPIE 1737 (1992) 2.
[18] A. Lempicki, J. Appl. Spectrosc.62 (1995) 209.
[19] N.F. Borelli, D.W. Hall, H.J. Holland, D.W. Smith,J. Appl. Phys.
61 (1987) 5399.
[20] H. Yukselici, P. Pearsans, T. Hayes, Phys. Rev.B52(1995) 11763.
[21] L.E. Brus, Appl. Phys. A Solids Surf.53 (1991) 465.
[22] C. Flyzanis, F. Hache, M.C. Klein, D. Ricard, SPIE1319(1990) 75.
[23] Q. Shen, T. Toyoda, Y. Hirose, K. Katayama, H. Yui,M.
Fujinami, T. Sawada, A. Harata, Analyt.Sci.17 (2001) 241.
[24] E.C. Scher, L. Manna, A.P. Alivisatos, Philos. Trans. R. Soc.
Lond. A 361 (2003) 241.
[25] W.C.W. Chan, D.J. Maxwell, X. Gao, R.E. Bailey, M. Han, S.
Nie, Curr. Opin. Biotech. 13 (2002) 40.
117
Structural and optical characterization of CdSe ….
[26] S.T. Selvan, T. Hayakawa,M. Nogami, J. Phys. Chem.
B103(1999) 7064.
[27] J. Mu, L. Xu, X. Li, Z. Xu, Q. Wei, H. Sun,S. Kang, J. Disper. Sci.
Technol. 27(2006) 235.
[28] M. Nogami, T. Hayakawa, Phys. Rev. B 56 (1997) 14235.
[29] M.H. Yukselici, J. Phys. Cond. Matter.14 (2002) 1153.
[30] V.C. Costa, Y.R. Shen, K.L. Bray, J. Non-Cryst. Solids 304 (2002)
217.
[31] P.D. Persans, L.B. Lurio, J. Pant, H. Yukselici, G. Lian, T.M.
Hayes, J. Appl. Phys. 87 (2000) 3850.
[32] V.P. Kunets, V.O. Yukhymchuk, M.Y. Valakh, Semicond. Phys.
Quantum Electron.4 (2001) 196.
[33] M.H. Yukselici, J. Phys.Cond. Matter.14 (2002) 1153.
[34] V.C. Costa, Y.R. Shen, K.L. Bray, J. Non-Cryst.Solids304(2002)
217.
[35] P.D. Persans, L.B. Lurio, J. Pant, H. Yukselici,G. Lian, T.M.
Hayes, J. Appl. Phys. 87 (2000) 3850.
[36] M. Andrianainarivelo, J.P Robert, Corriu, D. Leclercq, P.
Hubert Mutin, Andre Vioux, J.Mater. Chem. 7 (1997) 279.
[37] Venina dos Santos, C.P. Bergmann, Advances in Crystallization
Processes, InTech, Croatia(2012) 301.
[38] A.R.Kortan, R.Hull,R.L. Opila,M.G. Bawendi, L.E.Brus,J. Am.
Chem. Soc. 112 (1990) 1327.
118
Chapter 3
[39] E.J.C. Dawny, M.A. Fardad,M. Green, E.M. Yeatman,J. Mater.
Res.12 (1997) 3115.
[40] L.E Brus, J.Chem.Phys.79 (1983) 5566.
[41] Y. Kayanuma, Phys. Rev. B389(1998) 797.
[42] P.Lefbvre, Superlattices Microstruct.15 (1994) 447.
[43] P. Lefbvre, SPIE, Sol-Gel Opt.12288(1994) 163.
[44] P. Yang, M. Lu, Mater. Res. Bull. 36 (2001) 1301.
[45] S.Tamil Selvan, T. Hayakawa, M. Nogami, J. Lumin. 87 (2000)
532.
[46] A.K.
Adiyodi,
P.V.Jyothy,
Unnikrishnan, J. Optoelectro.
T.F.
Adv.
Toney,
G.Jose,N.V.
Mater.-Rapid Comm.1
(2007) 281.
[47] Vineet Kumar Rai, Cid B. de Araujo, Spectrochimica Acta Part
A 69 (2008) 509.
[48] P. Yang, C.F. Song, M.K. Lu, X. Yin, G.J. Zhou, D. Xu, D.R.
Yuan, Chem. Phys. Lett. 345 (2001) 429.
119