CdSiO3:Fe3+ nanophosphors: structural and luminescence

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.


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.


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.


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.


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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CdSiO3:Fe3+ nanophosphors: structural and luminescence