CdSiO3:Fe3+ nanophosphors: structural and luminescence
properties
KAMALA SOPPIN1 and B M MANOHARA2,*1 Department of Physics, DRM Science College, Davangere 577004, India2 Department of Physics, Government First Grade College, Davangere 577004, India
*Author for correspondence ([email protected])
MS received 24 July 2020; accepted 19 September 2020
Abstract. CdSiO3:Fe3? (1–9 mol%) nanophosphor was prepared by the propellant combustion technique. The powder
X-ray diffraction result shows the formation of highly crystalline nanophosphor monoclinic phase. The average particle
size was calculated using Scherrer’s formula and W–H plots were found in the range of 22–42 nm. The field emission
scanning electron microscope and transmission electron microscope pictures of the particle showed agglomerated, highly
porous, lots of voids, irregular shape and uneven in size. Fourier transform infrared and Raman spectroscopy were
recorded to investigate the nature of chemical bonds. Energy bandgaps (Eg) of the prepared samples were estimated using
Wood and Tauc relation from the optical UV–Visible spectroscopy and found to be *5.2 eV. Photoluminescence studies
of (1–9 mol%) CdSiO3:Fe3? nanophosphor shows an intense emission peak at 715 nm when excited at 361 nm. The
energy transfer of the excited Fe3? ions at higher concentrations are due to concentration quenching. As incorporation
concentration of Fe3? increases, 4T1 (4G) ? 6A1 transition dominates and the emission intensity increases. Commission
International De I’Eclairage and coordinated colour temperature of the phosphors were well located in red region.
Therefore, Fe3?-doped CdSiO3 nanophosphor was highly useful for the preparation of red component of WLED’s and
solid-state display applications.
Keywords. Nanophosphor; X-ray diffraction; transition electron microscope; energy gap; photoluminescence.
1. Introduction
Stable phosphors with suitable morphology and higher
yield are in great demand for energy saving applications,
like display, lasers, scintillators, safety indicators, etc. On
this regard, a silicate host is found to be multi-colour
phosphorescence and suggests inactive with alkali, oxy-
gen and acid environment [1,2]. The several silicates
CdSiO3 host reveals a notable optical and luminescent
property. The blended nature of ionic and covalent is due
to the presence of Cd2? ions and strong interaction
among Si–O is present inside the SiO3 organization. The
crystal structure of CdSiO3 shows a one-dimensional
chain of side-sharing SiO4 tetrahedron. As an end result,
dopants can be easily embedded into the host via
replacing the Cd site. In order to keep the charge neu-
trality, the charge compensation of Cd2? and O2- had
been tuned through the dopants. These dopants are
accountable for the creation of deep traps at appropriate
depths, which stores the excitation energy and emit the
light in the visible range. Consequently, to improve the
properties of the luminescent materials, the exothermic
reaction-based on combustion method was developed [3].
Transition metal ions (TMI) show fluorescence inside the
region 700–1100 nm. It is extensively used in luminescence
substances because of its strong visible absorption and
emission bands. Unfilled 3d3 electronics shell of the TMI has
a number of inner side energy levels, through which, optical
transitions arise to produce luminescent emission [4–6]. A
number of durable persistent luminescence materials dealt
with TMI, CdSiO3 has become a notable host. Due to the fact
that Fe3? ions can easily replace the Cd2? ions, the precise
host lattice crystal field strength around Fe3? ions. For red and
near-infrared photoluminescence (PL), trivalent Fe3? ions
become a positive emitting centre because of its wide-range
emissions. Thus we have taken these factors into considera-
tion and Fe3?-doped CdSiO3 (1–9 mol%) nanophosphors
have been synthesized by using propellant solution combus-
tion technique. The structural information of the prepared
phosphors have been examined through powder X-ray
diffraction (PXRD), field emission scanning electron micro-
scope (FESEM), transition electron microscope (TEM),
Fourier transform infrared spectroscopy (FTIR) and Raman
techniques. The optical properties of (1–9 mol%) Fe3?-doped
CdSiO3 nanophosphor was investigated by UV–Visible
absorption and PL studies.
Bull. Mater. Sci. (2021) 44:49 � Indian Academy of Scienceshttps://doi.org/10.1007/s12034-020-02332-ySadhana(0123456789().,-volV)FT3](0123456789().,-volV)
2. Preparation of Fe31-doped CdSiO3 nanophosphors
Fe3?-doped CdSiO3 (1–9 mol%) nanophosphors were
synthesized by propellant solution combustion technique
using a freshly prepared ODH (oxalyl dihydrazide) as a
fuel [7]. The stoichiometric composition of the redox
mixture was considered so that the maximum energy is
released during combustion. The flowchart for the syn-
thesis (1–9 mol%) of Fe3?-doped CdSiO3 nanophosphors
are shown in figure 1. Analar grade cadmium nitrate
(Cd(NO3)2�6H2O; Sigma Aldrich, 99.9%), tetraethyl
orthosilicate (TEOS: (CH3CH2O)4Si, 99.9%), iron nitrate
(Fe(NO3)3�9H2O; Sigma Aldrich, 99.9%) and ODH
(C2H6N4O2) were used as the starting materials. A suit-
able amount of (Cd(NO3)2�6H2O, (CH3CH2O)4Si and
(C2H6N4O2) (1:1:1.25 in mole ratio) were well dissolved
in *300 ml of double-distilled water and stirred well
using magnetic stirrer for 1 h to get homogenized aqueous
solution. The mixture was rapidly heated in a preheated
muffle furnace maintained at 500 ± 10�C.
The reaction takes place within few seconds by heating
the redox mixture to incandescence, leading to the forma-
tion of powder. The obtained final product was further
calcined at 800�C for 2 h for the formation of fine crys-
talline sample [8]. Composed chemical equation for the
formation of Cd1–xFexSiO3-d was given by using:
ð1 � xÞCdðNO3Þ2 þ xFeðNO3Þ3 þ C2H6N4O2
þðCH3CH2OÞ4Si ! Cd1�xFexSiO�d3ðsÞ þ 2CO2ðgÞ
þ3H2OðgÞ þ3 � x
2
� �N2ðgÞ ð1Þ
PXRD analysis was analysed by using Shimadzu X-ray
diffractometer (operating at 50 KV and 20 mA by means of
CuKa (1.541 A) radiation with a nickel filter at a scan rate
of 2� min-1). Data were collected in the range of 10�–60�.Morphology was analysed by using FESEM (ULTRA 55,
FESEM (Carl Zeiss), TEM and SAED pattern. FTIR spec-
trum was recorded along with KBr pellets. Raman studies
were carried out on a micro-Raman system from Jobin-
Yvon Horiba (LABRAM HR-800) spectrometer equipped
with a confocal aperture. UV–Vis spectra of the samples
were recorded with the SL 159 ELICO UV–Visible Spec-
trophotometer in the range of 200–800 nm. PL spectra were
carried out using Horiba (model Fluorolog-3) Spectrofluo-
rometer at room temperature using 450 W Xenon as exci-
tation source.
3. Results and discussion
3.1 Powder X-ray diffraction
Figure 2 shows the PXRD patterns of (1–9 mol%) Fe3?-
doped CdSiO3 nanophosphors calcined at 800�C for 2 h.
The diffraction peaks of (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors were matched with the JCPDS card No.
35-0810 and shows better crystallinity and monoclinic
phase. The average particle size ‘D’ was calculated by the
Scherrer’s formula and Williamson–Hall (W–H) plots. The
particle size ‘D’ of the (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors of all composition calcined at 800�C for 2 h
was in the range 22–42 nm. The particle size ‘D’ for which
the lattice pressure has been taken into consideration is
Figure 1. Flow chart for the synthesis of (1–9 mol%) Fe3?-
doped CdSiO3 nanophosphors calcined at 800�C for 2 h.
10 15 20 25 30 35 40 45 50 55 602θ (degree)
JCPDS NO. 35-0810
Inte
nsity
(a.u
)
(a)
(b)
(c)
(d)
(e)
(f)
(200
)(0
01)
(201
)
(-401
)(-2
02)
(-11
1)(2
02)
(310
)(-
311)
(311
)(0
12)
(402
)(-
312)
(-20
3)(5
11)
(020
)
(413
)
(712
)
Figure 2. PXRD of (a) Pure and (b–f) (1–9 mol%) Fe3?-doped
CdSiO3 nanophosphors.
49 Page 2 of 9 Bull. Mater. Sci. (2021) 44:49
shown in figure 3. Lattice strain and average particle size
‘D’ had been predicted from these techniques, as shown in
table 1. The lattice strain was taken as an standard error of
± 0.4 9 10-3.
Proper percent difference in ionic radii among incorpo-
ration and substituted ions should not exceed 30%. Calcu-
lations of the radius percentage variance (Dr) among the
incorporation Fe3? ions and replaced Cd2? ions in CdSiO3:
Fe3? were performed using the below formula,
Dr ¼Rm CNð Þ � Rd CNð Þ
Rm CNð Þ ; ð2Þ
where CN is co-ordination number, Rm(CN) the radius of
host cations and Rd(CN) the radius of dopant ions. Rd(CN)
is found to be 27.98%. It was obvious that the Fe3? ionic
radius was close to that of Cd2? replaced with Fe3? ions in
the CdSiO3 host. Hence, it is considered that Cd2? sites
were exchanged by Fe3? in this lattice [9].
3.2 Morphological analysis
TEM and FESEM had been vital tools for the characteri-
zation of nanomaterials, as they deliver data about the
morphology of the materials. Figure 4a–e indicates the
FESEM micrographs of (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors. It was determined that the samples have
been mainly porous, agglomerated, plenty of voids and
fluffy with polycrystalline nature.
TEM micrographs of CdSiO3:Fe3? (1–9 mol%) nano-
phosphors were shown in figure 5a–e. It contains uneven
size shaped particles with an average particle size of
*80 nm and polycrystalline nature of the sample shows the
SAED patterns in figure 5f.
3.3 Fourier transform infrared spectroscopy
FTIR spectra of (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors was recorded in the range of
400–4000 cm-1, shown in figure 6. A spectrum shows the
broad band in the range 850–1200 cm-1 due to irregular
stretching vibration of Si–O–Si bond and stretching vibra-
tions of edge Si–O bonds. The peaks at 458, 552 and
638 cm-1 were the characteristic stretching vibrations of
Si–O–Si bridges. A weak absorption peak at 2852, 2917 and
3415 cm-1 indicates the presence of C=O bond in the
structure [10]. Sharp peak corresponding to 883, 934, 1013
and 1071 cm-1 can be ascribed to Si–O bond, which exists
in the form of SiO3.
3.4 Raman spectroscopy
Figure 7 shows Raman spectra of (1–9 mol%) Fe3?-doped
CdSiO3 nanophosphors. Raman spectra have been carried
out at room temperature within the range 100–1200 cm-1.
The positions of the vibrational modes located at
70–213 cm-1 had been attributed to the Cd–O vibrational
modes and also Si–O–Si symmetric bending [11]. The band
witnessed at 308 and 399 cm-1 was given to the symmet-
rical stretching or bending vibrations of Si–O–Si bonds,
which was shaped by corner sharing of SiO3 polyhedral
[12]. Peak at 630 cm-1 was attributed to the axial sym-
metrical stretching vibrational modes of (c4) SiO42- [13].
Peak at 700 cm-1 was associated with the existence of two
linked tetrahedral (sorosilicate) (Si2O7)6- or isolated tetra-
hedral (neosilicates) (SiO4)4- group ‘Q0’ without bending
oxygen. Width of peak at 961 cm-1 is characteristic of ‘Q1’Figure 3. W–H plots of (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors.
Table 1. Estimated structural parameters of pure and
(1–9 mol%) Fe3?-doped CdSiO3 nanophosphors.
Mol%
Scherrer’s equation
(nm)
W–H plot
(nm)
Lattice strain
(910-3)
Pure 23 32 2.16
1 36 42 1.77
3 33 22 0.25
5 29 22 0.65
7 28 20 0.52
9 29 25 1.09
Bull. Mater. Sci. (2021) 44:49 Page 3 of 9 49
and ‘Q2’ of tetrahedral with 1 and 2 binding oxygen,
respectively. Peak at 1000 cm-1 originate from c1 and c2
stretching vibrations of Si–O (SiO4- stretching). Based on
the lattice strain variant inside the compounds predicted
from PXRD, Raman spectra had lesser shifts inside the
vibrational modes.
3.5 UV–Visible absorption spectroscopy
Inset of figure 8 shows UV–Visible absorption spectra
of (1–9 mol%) Fe3?-doped CdSiO3 nanophosphor
samples absorbed at 245 nm. Energy bandgap (Eg) of
synthesized samples was calculated using Wood and
Figure 4. FESEM images of (a–e) (1–9 mol%) Fe3?-doped CdSiO3 nanophosphors.
49 Page 4 of 9 Bull. Mater. Sci. (2021) 44:49
Tauc relation, shown in figure 8. Calculated value of Eg
was found to be *5.2 eV of the standard error
±0.2 eV, shown in the table of inset of figure 8 [14].
Hence it confirms that the prepared (1–9 mol%)
Fe3?-doped CdSiO3 nanophosphor samples are insulat-
ing material.
3.6 PL studies
The excitation spectra of Fe3? (3 mol%)-doped CdSiO3
nanophosphor recorded at room temperature is shown in
figure 9. The excitation of Fe3?-doped CdSiO3 nanophos-
phor is more intense at 361 nm and less intense at 375 nm.
Figure 5. TEM micrographs of (a–e) (1–9 mol%) and (f) SAED of Fe3?-doped CdSiO3
nanophosphors.
Bull. Mater. Sci. (2021) 44:49 Page 5 of 9 49
The Fe3? belongs to d3 configuration with the impact of
octahedral symmetry field, the ground state 4F. In addition
to the terms of exited free electron states, which includes 4P,2G will break up into a number of quartet and doublet terms
as 4A2g, 4T2g, 4T1g, 2Eg, 2T1g, 2T2g, 2A1g, etc. Out of which4A2g lies lowest according to Hund’s rule. In a wide cate-
gory of oxide host systems, the Fe3? had been continually
oxygen coordinated with six nearest neighbours, feasible in
pure octahedral, teraoctahedral or distorted octahedral
symmetry site. The strong wide band is at 361 nm
(c1 = 27700 cm-1), whereas weak band is at 375 nm
(c2 = 26667 cm-1) selected 4A2g (F) ? 4T1g (F)
transition.
The ðc1Þ band gives the crystal field splitting parameter
of 10.15 Dq. The Racah parameter ‘B’ was calculated by
assigning a mean value for the ðc2Þ bands by using the
relation [15]:
B ¼ 2c21 þ c2
2 � 3c1c2
15c2 � 27c1
ð3Þ
Intended Racah parameter (B) of Fe3? had been discov-
ered to be 83.58 cm-1. Value of inter-digital repulsion
parameter Bfree for Fe3? ions was 814 cm-1. A comparison
with these observations suggests that ‘B’ was reduced by
using 11% from the free ion value. According to Tanabe–
Sugano diagram, the crossing of the 2E and 4T2 levels Dq/
B is better than 2.3, which correspond to strong crystal field.
In the present report, the value of Dq/B was observed to be
*33.14, which suggests that Fe3? ions have been located in
strong crystal field [16].
Emission spectra for CdSiO3:Fe3? (1–9 mol%) samples
excited with UV light source (361 nm) at room temperature
4000 3500 3000 2500 2000 1500 1000 500
9 mol%
7 mol%
5 mol%
3 mol%
% T
rans
mitt
ance
(a.u
)
Wavenumber (cm-1)
45855
2638
883
934
1013
10
71
2852
2917
3415
1 mol%
Figure 6. FTIR spectra of (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors.
Figure 7. Raman spectra of (1–9 mol%) Fe3?-doped CdSiO3
nanophosphors.
Figure 8. Eg of (inset: UV–Visible spectra and table shows Eg
values) (1–9 mol%) Fe3?-doped CdSiO3 nanophosphors.
360 370 380 390
8.0x106
1.2x107
1.6x107
2.0x107
375 nmInte
nsity
(cps
)
Wavelength(nm)
361 nm
Figure 9. Excitation spectra of 5 mol% Fe3?-doped CdSiO3
nanophosphors.
49 Page 6 of 9 Bull. Mater. Sci. (2021) 44:49
are shown in figure 10. Maximum intense energy band at
715 nm and the intermediate band located at 615 nm were
accredited to 4T1 (4G) ? 6A1 (6S) and 4T2 (4G) ? 6A1 (6S)
transitions, respectively. Developed energy band located at
573 nm was related to 4E ? 4A1 (4G) ? 6A1 (6S) transi-
tions of Fe3? ions [17]. Fe3? emissions from greater excited
states (in blue green region) were once in a while, but have
been observed for each tetrahedral and octahedral site. The
determined spectra have been related to spin-forbidden
transitions of Fe3? tetrahedral coordinated by using O2-
ligand anions.
The variant of PL intensity with Fe3? attention is shown in
figure 11. Figure explains that the luminescence intensities at
715 nm of the CdSiO3:Fe3? phosphors will increase with the
increase of Fe3? ion concentration. The intensity is maximum
for 3 mol% of Fe3? ion and then decreases with a further
increase of concentration. Because of its energy transfer, the
various excited Fe3? ions are at higher concentrations which
is due to concentration quenching. As dopant concentration
of Fe3? ions increases, 4T1 (4G) ? 6A1 transition leads to the
emission intensity. This may be attributed to the increasing
distortion of the nearby field around the Fe3? ions. Moreover,
there was a charge imbalance inside the host lattice because
of incorporation of Fe3? cations. The reason is that after the
concentration of Fe3? ions increase, the interaction among
the dopant ions also increases, resulting in self-quenching
and PL intensity decreases. The critical energy transfer dis-
tance (Rc) was calculated as discussed. Non-radiative energy
transfer distance (Rc) can be expected by using the relation
proposed by Blasse [18].
Rc ¼ 23V
4pXcN
� �1=3
; ð4Þ
where Xc is the critical concentration, N the number of
cation sites and V the volume of the unit cell. For
CdSiO3:Fe3?, the values of N, V and Xc were 6, 379.65 A´ 3
and 0.03, respectively. Using these parameters, the expected
Rc was found to be 15.91 A´
. Since Rc was not less than 5 A,
exchange interaction was not responsible for non-radiative
energy transfer method from one Fe3? ions in to another.
According to Blasse theory, radiative exchange multi-
pole–multipole interaction can be observed in Fe3? ion
incorporation samples. In which the energy transfer process
may also be due to multipolar interaction. In order to decide
the type of interaction involved in the energy transfer, Van
Uitert’s [19], the emission mechanism of Fe3? in CdSiO3
nanophosphors can be proposed as follows. The emission
intensity (I) per activator ion follows the equation,
I
x¼ k 1 þ b xð Þh=3
h i�1
; ð5Þ
where x was the activator concentration, I/x was the emis-
sion intensity (I) per activator ion, k and b were constants
for a given host under the same excitation condition.
According to equation (5), h = 3 for the energy transfer
among the nearest-neighbour ions (exchange interaction),
while h = 6, 8 and 10 for dipole–dipole (d–d), dipole–
quadrupole (d–q) quadrupole–quadrupole (q–q) interac-
tions, respectively. Assuming that b(x)h/3[[1, equation (5)
can be specified as follows:
logI
x¼ k1 � h
3 log x: ð6Þ
From the slope of equation (6), the electric multipolar
character (h) can be obtained by the slope (-h/3) of the plot
log(I/x) vs. log x. It was observed from figure 12, Fe3?-
doped CdSiO3 nanophosphors of log(I/x) on log x was
550 600 650 700
8.0x106
1.0x107
1.2x107
1.4x107
1.6x107
CdSiO3:Fe3+
687 nm
1 mol %
7 mol%
9 mol %
5 mol%
3 mol%
715
nm
615 nm573 nm
Inte
nsity
(cps
)
Wavelength (nm)
λexci = 361 nm
Figure 10. PL emission spectra of (1–9 mol%) Fe3?-doped
CdSiO3 nanophosphors.
0 2 4 6 8 10Fe3+ Concentration (mol%)
615 nm
522 nm
687 nm
715 nm
PL In
tens
ity (a
.u)
Figure 11. Variation of PL intensity with (1–9 mol%) Fe3?-
doped CdSiO3 nanophosphors.
Bull. Mater. Sci. (2021) 44:49 Page 7 of 9 49
linear. The slope and multipolar character ‘h’ was found to
be -0.95625 and 6.19905, respectively, which was close to
6. Therefore, the concentration quenching in CdSiO3:Fe3?
phosphor occurred due to dipole–dipole interaction.
The Commission International De I’Eclairage (CIE)
coordinates for (1–9 mol%) CdSiO3:Fe3? nanophosphors as
a function of Fe3? concentration for the luminous colour was
illustrated by the PL spectra. Red long-lasting phosphores-
cence was witnessed in CdSiO3:Fe3? nanophosphor and its
corresponding regions are marked in figure 13a with stars in
red region, their X and Y values are given in the table inset of
figure 12. Literature showed that the Fe3? doping outcome
becomes stronger in the case of particles with greater crys-
tallinity, resulting in an better activation degree of Fe3?.
Therefore, the current phosphors were useful as a replace-
ment for those of natural white light [20,21]. Also, average
coordinated colour temperature (CCT; figure 13b) of
(1–9 mol%) CdSiO3:Fe3? nanophosphor was found to be
6177 K, shown in inset of figure 13b.
4. Conclusions
The (1–9 mol%) Fe3?-doped CdSiO3 nanophosphors were
successfully prepared via solution combustion technique.
PXRD of all samples were well matched with JCPDF No.
35-0810 and shows monoclinic phase without any impurity
peaks. Particle size ‘D’ was expected to be in the range
22–42 nm. FESEM and TEM show morphological study of
(1–9 mol%) Fe3?-doped CdSiO3 nanophosphors with
agglomerated, fluffy and uneven in size. The CdSiO3:Fe3?
nanophosphor is insulators with Eg * 5.2 eV. PL emission
spectra display that there may be an increase in emission
intensity with increase in Fe3? concentrations up to 3 mol%
and after that emission quenching was determined. Narrow
red emissions, peak observed at 715 nm in CdSiO3:Fe3? is
due to 4T1 ? 6A1 transition from Fe3? ions. CIE and CCT
co-ordinates are situated in the red regions, hence the pre-
pared (3 mol%) nanophosphor might be useful in red
component of white light-emitting diode’s, also can be used
in solid-state display applications.
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