Effect of synthesis temperature on morphological and luminescent properties of lithium fluoride crystals

Article abstract of DOI:10.1166/jnn.2017.13801

The precipitation method was used to synthesize pure lithium fluoride crystals using water as solvent at different synthesis temperature, from 10 to 90 °C. The effect of temperature on crystalline structure, sizes of cube like particles, and the luminescent response is reported. The synthesized materials were characterized by scanning electron m icro scopy and their morphology and size distributions were determined. Particle sizes were found to be de pendent on the synthesis temperature, varying from 1.38 to 9.01 μm. A single cubic cr ystalline phase was determined by X-ray diffraction (XRD) for all synthesized samples. The photoluminescence (PL) spectra as well as UV-Vis absorbance were also analyzed and showed a clear dependence with the particle size. The thermoluminescent (TL) response to X-ray irradiation was studied for an exposition of 43 R. A TL intensity dependence of lithium fluoride crystals with the synthesis temperature is observed. The micro crystalline cube size can be controlled by varying the synthesis temperature.

Full text of DOI:10.1166/jnn.2017.13801

Article
Journal of
Nanoscience and Nanotechnology
Vol. 17, 5612–5616, 2017
Copyright © 2017 American Scientific Publishers
All rights reserved
Printed in the United States of America
www.aspbs.com/jnn
Effect of Synthesis Temperature on Morphological and
Luminescent Properties of Lithium Fluoride Crystals
1
1
1
1
1
Miguel A. Vallejo , Esteban Rivera , Juan C. Azorín , Jesús Bernal , Cristhoper Camacho ,
2
3
4
1ꢀ∗
Ricardo Navarro , Emma K. Encarnación , Luis A. Díaz-Torres , and Modesto A. Sosa
1Universidad de Guanajuato, Campus León, División de Ciencias e Ingenierías, Loma del Bosque 103,
Colonia Lomas del Campestre, 37150 León, Gto., México
Universidad de Guanajuato, Campus Guanajuato, División de Ciencias Naturales y Exactas, Cerro de la Venada S/N,
Pueblito de Rocha, C.P. 36040 Guanajuato, Gto., Méxic
2
3
Universidad Autónoma de Santo Domingo, Departamento de Física, Facultad de Ciencias, Ciudad Universitaria,
Santo Domingo, 11114, República Dominicana
Grupo de Espectroscopia de Materiales Avanzados y Nanoestructurados (GEMANA), Centro de Investigaciones
4
en Óptica, A.P. 1-948, León, Gto., México
The precipitation method was used to synthesize pure lithium fluoride crystals using water as sol-
ꢀ
vent at different synthesis temperature, from 10 to 90 C. The effect of temperature on crystalline
structure, sizes of cube like particles, and the luminescent response is reported. The synthesized
materials were characterized by scanning electron microscopy and their morphology and size distri-
IP: 95.85.80.158 On: Mon, 09 Mar 2020 18:08:08
butions were determined. Particle sizes were found to be dependent on the synthesis temperature,
Copyright: American Scientific Publishers
varying from 1.38 to 9.01 ꢀm. A single cubic crystalline phase was determined by X-ray diffrac-
Delivered by Ingenta
tion (XRD) for all synthesized samples. The photoluminescence (PL) spectra as well as UV-Vis
absorbance were also analyzed and showed a clear dependence with the particle size. The ther-
moluminescent (TL) response to X-ray irradiation was studied for an exposition of 43 R. A TL
intensity dependence of lithium fluoride crystals with the synthesis temperature is observed. The
micro crystalline cube size can be controlled by varying the synthesis temperature.
Keywords: LiF Crystals, Synthesis Temperature, Luminescent Properties.
1
. INTRODUCTION
nanocrystalline LiF:Mg, Cu, P rods and studied their TL
properties for gamma radiation at exposure level up to
10 kGy.
Lithium fluoride (LiF) has become one of the most widely
used materials for radiation dosimetry purposes. Many
publications have reported the response of LiF in various
radiation fields and a wide range of doses, as also the effect
Some authors have paid attention to the dependence of
the LiF crystal characteristics as well as the TL response
1
–5
9ꢀ10
of different elements used as dopants.
on the preparation method.
In a recent paper Alharbi
1
1
The response of LiF:Mg, Ti (TLD-100) has been exten-
sively studied and compared with many other materials,
et al. synthesized Ag doped LiF using a new chemi-
cal co-precipitation method. They used as co-solvent an
ethanol:water mixture with different ratios, and found a
dependence of the UV-Vis absorbance and photolumines-
cence response as well as the size of the crystals. The
authors report micro and nano crystalline cubes whose
size can be controlled between 10 ꢁm–50 nm by vary-
ing the solvent:co-solvent ratio. They observed that the
larger crystals were grown using water as a solvent,
while by using ethanol as co-solvent, increasing ethanol
concentration results in a reduced cube particle, down to
the nanometric range.
such as LiF:Mg, Cu, P (TLD-100H).6 Davis et al. irra-
diated both materials using photon beams from cobalt-60
with energies from 25 to 1100 keV and found the TL
responses to be markedly different in energy dependence.
ꢀ7
6
7
In other work Freire et al. found that TLD-100 and TLD-
1
00H present similar reproducibility and well linearity of
results, however the TLD-100H shows a higher residual
signal and less energy variation. Salah et al. produced
8
∗
Author to whom correspondence should be addressed.
5612
J. Nanosci. Nanotechnol. 2017, Vol. 17, No. 8
1533-4880/2017/17/5612/005
doi:10.1166/jnn.2017.13801

Vallejo et al.
Effect of Synthesis Temperature on Morphological and Luminescent Properties of LiF Crystals
Also, Vallejo et al.12 used the co-precipitation method
to synthesize pure and Ag-doped LiF crystals and they
reported the effect of crystalline cube sizes and Ag con-
centration on the TL response. They observed two effects,
the first concerns with a significant dependence of the TL
intensity on the size of the crystals, being larger for the
smallest crystals for pure LiF, and second, for Ag-doped
samples the TL intensity augmented almost linearly with
the Ag concentration. They pointed out that the effect of
grain size on the TL response could be explained by the
increasing of specific area at the surface of lower grains,
giving rise to an enhancement of TL properties as the grain
size decreases, due to the fact that during the TL reading
a larger area of material is exposed.
2.2.2. XRD Analysis
The XRD properties of the samples were obtained using
a Bruker D2 Phaser (Coventry, United Kingdom) diffrac-
tometer with Cu Kꢂ radiation, which can measure a range
ꢀ
ꢀ
of 2ꢃ from 3 to 140 , using a voltage of 30 kV and a
current of 10 mA. The samples were prepared by plac-
ing the crystals on silicon wafer. The analysis time was
20 min for each of the samples, using the value for 2ꢃ
ꢀ
ꢀ
ꢀ
in a range from 30 to 70 , and an increase of 0.020
every 0.5 s. For the analysis of the results, the software
Difracc-Commander was used. For parameter interpreta-
tion of the spectra, the Difracc-EVA complementary soft-
ware was used for database comparison.
In the present work a precipitation method is used to
synthesize pure LiF crystals by using different synthesis
temperature to control the size of the particle products.
The synthesized materials were characterized by XRD and
scanning electron microscopy (SEM), and their structure,
morphology and size distributions were determined. The
effect of temperature on crystalline cube sizes and the
luminescent response was investigated.
2.2.3. UV-Vis Absorbance and
Photoluminescence Analysis
The UV-Vis absorbance spectra of the samples were
obtained using a Cary 5000 UV-Vis-NIR (Agilent Tech-
nology, Santa Clara, CA, USA) spectrophotometer, at
room temperature. Spectra were recorded between 200 and
1
100 nm. The samples were placed in a special container,
which compressed the crystals forming a thin film. To
avoid losses and to get a better response an integrating
sphere was used.
2
2
. EXPERIMENTAL PROCEDURE
.1. LiF Crystal Synthesis
Synthesis of LiF crystals was carried out by precipita-
IP: 95.85.80.158 On: Mon, 09 Mar 2020 18:08:08
Pellets were made with 4.5 g of LiF powders applying
1
.5 tons on a pressing die of 13 mm diameter. Photolumi-
nescence (PL) measurements were carried out by using a
5 W Xe lamp and an Acton Pro 1500i monochromator
tion, using tri-distilled water as synthesis media. Samples
Copyright: American Scientific Publishers
7
were synthesized at five different temperatures, from 10
Delivered bya sI n egx ec ni t taat ion source in the 200 to 500 nm range. The fluo-
ꢀ
to 90 C.
rescence emission was analyzed with a second Acton Pro
For the LiF synthesis, lithium chloride (LiCl) and
2
300i monochromator and a R955 Hamamatsu photomul-
ammonium fluoride (NH F) of analytical reagent grade
4
tiplier tube. The system was controlled with a PC where
excitation and emission spectra were recorded.
purity were used as precursor materials. All syntheses were
carried out using 3.84 N LiCl solution prepared in tri-
distilled water. This solution was placed in a glass burette
and then dropwise with continuous stirring during 1 hour
2
.2.4. Thermoluminescence Analysis
Thermoluminescent response of samples was measured
using a TL Reader Harshaw 3500, Thermo Scientific
on a 3.84 N NH F solution prepared in a plastic beaker.
4
Each precursor material was dissolved in 50 mL water sol-
vent for a total volume of 100 mL. Then, precipitates were
filtered out and washed 25 times in tri-distilled water at
room temperature. The final precipitated (about 5 g of LiF)
was dried in a convection oven, model ED23 (Binder Inc.,
ꢀ
(
UK). First the dosimeters were annealed at 400 C during
1
(
7
h, on a ceramic plate, using a muffle MA12D, Terlab
Mexico). For irradiation an X-ray machine Elity 70E RX-
0KUP (C.I. Dental XRay S.A.S., USA) was used to apply
ꢀ
43 R of exposition. After irradiation dosimeters reading
was held in an inert atmosphere of nitrogen. A preheat
NY, USA) at 70 C for 2 h.
ꢀ
ꢀ
−1
temperature of 50 C, acquire temperature rate of 10 C s
2
.2. Sample Characterization
ꢀ
and maximum temperature of 300 C were used for the
glow curve acquisition.
2
.2.1. Morphology Analysis
SEM analyses were performed using a scanning electron
microscope Zeiss, EVO HD15 LS (Germany) to observe
the crystals morphology. Before analysis, LiF crystal sam-
ples were metalized by gold sputtering in a Fine Coat Ion
Sputter Jeol JFC-1100. The morphology of the samples
was observed using secondary electron flux. The acceler-
ating voltage was in the range 5–11 kV and the magnifi-
cation was 4.00 kX. Particle size distribution was obtained
by SEM image analysis using the ImageJ software.
3
. RESULTS AND DISCUSSION
3.1. SEM Analysis
Figure 1 shows the synthesis temperature effect on the
obtained LiF particle sizes. It is observed that the crystal
cube size increases as the synthesis temperature increases.
The mean sizes vary from 1.38 to 9.01 ꢁm, as the tem-
ꢀ
perature goes from 10 to 90 C, respectively (see Table I).
J. Nanosci. Nanotechnol. 17, 5612–5616, 2017
5613

Effect of Synthesis Temperature on Morphological and Luminescent Properties of LiF Crystals
Vallejo et al.
IP: 95.85.80.158 On: Mon, 09 Mar 2020 18:08:08
Copyright: American Scientific Publishers
Delivered by Ingenta
Figure 1. SEM images of pure LiF crystals synthesized at different temperatures.
These results can be compared to that reported using
a precipitation method with a co-solvent ethanol:water as
3.2. XRD Analysis
Figure 2 shows the XRD pattern for pure LiF samples
synthesized at different temperatures. All curves show well
defined peaks at 2ꢃ = 38 , 45 and 66 . All samples show
a complete cubic phase, however the peaks show slight
changes according to the temperature of synthesis. In the
1
1ꢀ12
synthesis media.
The authors report that cube size can
ꢀ
ꢀ
ꢀ
be controlled by varying the solvent:co-solvent ratio. In
this work we have demonstrated that the cube size can be
controlled varying the synthesis temperature and using just
water as synthesis media. In both cases, the observed effect
can be attributed to changes in solubility (due to temper-
ature or solvent polarity modifications), which determines
the crystal growth dynamics.
ꢀ
curve T1 obtained at 10 C, peaks are significantly wider
than the others, which means either a small sizes of crystal
or lower crystallinity grade (see Table II). The assumption
of a small crystal size at lower temperatures is confirmed
by the SEM analysis, where a mean size of 1.38 ꢁm was
ꢀ
Table I. Mean size of LiF crystals as a function of synthesis
temperature.
obtained for the sample at 10 C.
3
.3. UV-Vis Absorbance and
Photoluminiscence Analysis
Temperature
Mean size
(ꢁm)
Standard deviation
ꢀ
Sample
( C)
(ꢁm)
Figure 3 shows the UV-Vis absorption spectra for LiF crys-
tals synthesized using five different temperatures. A broad
band centered in 436 nm is observed showing some depen-
dence on the temperature. The results show a clear mono-
tonic dependence of the intensity of the absorbance as a
T1
T2
T3
T4
T5
10
23
50
70
90
1ꢄ38
4ꢄ10
4ꢄ60
8ꢄ90
9ꢄ01
0ꢄ90
1ꢄ40
2ꢄ43
3ꢄ73
2ꢄ56
5614
J. Nanosci. Nanotechnol. 17, 5612–5616, 2017

Vallejo et al.
Effect of Synthesis Temperature on Morphological and Luminescent Properties of LiF Crystals
T1
1
1
1
.4
.2
.0
T1 (10ºC)
T2 (23ºC)
T3 (50ºC)
T4 (70ºC)
T5 (90ºC)
T5 (90ºC)
T2
T3
T4 (70ºC)
T3 (50ºC)
T2 (23ºC)
T1 (10ºC)
0.8
0
0
0
0
.6
.4
.2
.0
T4
T5
3
50 400 450 500 550 600 650 700 750 800 850 900
Wavelength (nm)
30
35
40
45
50
55
60
65
70
Figure 4. PL emission spectra of pure LiF samples at different
temperatures.
Angle(2Θ)
Figure 2. XRD pattern of pure LiF crystals synthesized at different
temperatures.
PL emission spectra, under 325 nm excitation, of syn-
thesized LiF samples using different temperatures are pre-
sented in Figure 4. The PL emission spectra shows two
peaks corresponding to two emissions bands centered in
Table II. Half widths of the peaks obtained by XRD and shown in
Figure 2.
4
23 nm and 825 nm, respectively. Both peaks correspond
Sample
Half widths (angle 2ꢃ)
to emissions due to intrinsic defects and aggregates, gen-
erated by F color centers.
ꢀ
ꢀ
ꢀ
ꢀ
T1 (10 C)
T2 (23 C)
T3 (50 C)
T4 (70 C)
0ꢄ606
0ꢄ237
2
IP: 95.85.80 0. ꢄ 14 52 28 On: Mon, 09 Mar 2020 18:08:08
3.4. Thermoluminiscence Analysis
Copyrig h0 ꢄ t4: 2 A2 merican Scientific Publishers
ꢀ
T5 (90 C)
0ꢄ4 4D 8elivered byTI hn eg eT nL t ar esponse intensity of the synthesized crystals was
measured for an exposition of 43 R using an X-ray source
during a total time of 52 s. Figure 5 shows the glow curves
function of the temperature of synthesis, which could be
associated to the size of the crystals. The band observed
in 436 nm is well known to be characteristic of LiF,
for pure LiF crystals synthesized at different temperatures.
ꢀ
A TL peak at 230 C is observed in all cases, except for
1
3
ꢀ
ꢀ
the sample at 90 C, which is shifted to 212 C. No signifi-
cant differences were observed in the glow curve structure,
neither in the characteristic energy, since all glow curves
corresponding to F color centers.
2
exhibit a single peak around the same temperature, about
0
0
0
0
0
0
.07
.06
.05
.04
.03
.02
ꢀ
2
00 C. However, the smallest crystals, (1.38 ꢁm), corre-
T1 (10ºC)
T2 (23ºC)
T3 (50ºC)
T4 (70ºC)
T5 (90ºC)
ꢀ
sponding to samples synthesized at 10 C show the highest
T2
T1
T1 (10ºC)
8
6
4
2
0
000
000
000
000
T2 (23ºC)
T3 (50ºC)
T4 (70ºC)
T5 (90ºC)
T1
T3
T2
T4
T5
T3
T4
1
0ºC
23ºC
0ºC
0ºC
90ºC
T5
5
7
300
400
500
600
700
800
900
1000
150
200
250
300
Wavelength (nm)
Temperature ºC
Figure 3. UV-Vis absorption spectra of pure LiF samples at different
Figure 5. TL intensity curves of pure LiF synthesized at different
temperatures.
temperatures.
J. Nanosci. Nanotechnol. 17, 5612–5616, 2017
5615

Effect of Synthesis Temperature on Morphological and Luminescent Properties of LiF Crystals
Vallejo et al.
intensity, which could be explained by the increasing of
specific area at the surface of lower grains, giving rise to an
enhancement of TL properties as the grain size decreases,
due to the fact that during the TL reading a larger area of
2014 and CIO-UG 2015. Authors thank Guanajuato
University-CONACYT National Laboratory for SEM
analysis.
1
2
TL material is exposed.
References and Notes
1
2
. W. Shoushan, Radiat. Prot. Dosim. 25, 133 (1988).
. P. Bilski, M. Budzanowski, and P. Olko, Radiat. Prot. Dosim. 65, 195
(1996).
4
. CONCLUSIONS
Undoped LiF crystals were synthesized and the effect of
temperature on crystalline cube sizes was studied. We
found a clear dependence of the crystal size on the syn-
thesis temperature. We found that the mean crystal size
increases as the synthetization temperature increases. This
dependence can be attributed to changes in solubility due
to the temperature, which favors different dynamics of
crystal growth. No changes were observed in the morphol-
ogy beyond the difference in crystal size.
3. A. Horowitz and Y. S. Horowitz, Radiat. Prot. Dosim. 33, 267
1990).
(
4
5
6
. J. I. Lee, J. L. Kim, A. S. Pradhan, B. H. Kim, K. S. Chung, and
H. S. Choe, Radiation Measurements 43, 303 (2008).
. J. I. Lee, J. L. Kim, S. Y. Chang, K. S. Chung, and H. S. Choe,
Radiat. Prot. Dosim. 115, 340 (2005).
. S. D. Davis, C. K. Ros, P. N. Mobit, L. Van der Zwan, W. J. Chase,
and K. R. Shortt, Radiat. Prot. Dosim. 106, 33 (2003).
7. L. Freire, A. Calado, J. V. Cardoso, L. M. Santos, and J. G. Alves,
Radiation Measurements 43, 646 (2008).
8. N. Salah, P. D. Sahare, and A. A. Rupasov, J. Lumin. 124, 357
The PL emission and the UV-Vis absorbance spectra
show a clear dependence on crystal size. Both the UV-Vis
absorbance and the emission increases as the crystal size
decreases. The TL response to X-ray irradiation was also
studied for an exposition of 43 R.
A thermoluminescent intensity dependence of lithium
fluoride crystals with the synthesis temperature was
observed. Also, it is important to stress the relevance of
having a synthesis method that is simpler than when using
co-solvents as synthesis media.
(2007).
9. N. Salah, N. D. Alharbi, S. S. Habib, and S. P. Lochab, Nuclear
Measurements and Methods Physics Reearch Section B 358, 201
(
2015).
0. N. Salah, N. D. Alharbi, and S. S. Habib, J. Lumin. 161, 313
2015).
1. N. D. Alharbi, N. Salah, S. S. Habib, and E. Alarfaj, Journal Physics
D: Applied Physics 46, 035305 (2013).
1
1
(
12. M. A. Vallejo, M. A. Sosa, E. Rivera, J. C. Azorín, J. Bernal,
R. Navarro, E. K. Encarnación, and L. A. Díaz-Torres, Nano
Acknowledgments: This workI Pw :a 9s 5 p. 8a r5t i. a8 l0l y. 1 s5u 8p pOo nr t: e Md on, 09 1M1 ,a1r6 52 000 24 10 ( 21 081 :6 0) .8:08
by the University of Guanajuato un Cd eo rp yg rr iagn ht st : CA ImO e- Ur i cG an S c1 3i e. n Gt i. f Bi cal Pd a uc cb hl ii ns i h, Je.rLsumin. 100, 333 (2002).
Delivered by Ingenta
Received: 16 March 2016. Accepted: 25 July 2016.
5616
J. Nanosci. Nanotechnol. 17, 5612–5616, 2017