Journal of Fluorescence

https://doi.org/10.1007/s10895-018-2265-9

ORIGINAL ARTICLE

Synthesis, Photophysical, Electrochemical and Thermal Investigation

of Anthracene Doped 2-Naphthol Luminophors and their Thin Films
for Optoelectronic Devices
K. G. Mane 1 & P. B. Nagore 1 & S. R. Pujari 2

Received: 4 April 2018 / Accepted: 9 July 2018

# Springer Science+Business Media, LLC, part of Springer Nature 2018

Abstract
A series of novel luminophors of 2-naphthol by doping anthracene were prepared using conventional solid state reaction
technique. The photophysical, electrochemical and thermal properties were studied by Fluorescence spectroscopy, XRD,
SEM, TGA-DSC and by Cyclic Voltammetry techniques. The thin films were characterized by Fluorescence spectroscopy.
XRD study of fine grained powders exhibited sharp peaks which specify crystallinity and homogeneity of the doped
luminophors. The fluorescence spectra of doped 2-naphthol exhibited emission of anthracene at 413 nm i.e. blue emission with
instantaneous fluorescence quenching of 2-NP due to excitation energy transfer (EET). Electrochemical data specify that the
HOMO and LUMO energy levels of the synthesized luminophors are in the range of 5.55–5.71 eV and 3.03–3.24 eV, respec-
tively. TGA-DSC study confirmed thermal stability of prepared luminophors. Hence, overall study proposes that these
luminophors seems applicable to be used as n-type materials for Optoelectronic devices.

Keywords n-type materials . Fluorescence quenching by EET . Organic luminophors

Introduction in solid-state reactions for lightening. Hence, these mesmeriz-

ing properties attracted various researchers and added more to
Nowadays organic semiconductors have attracted more atten- existing literature which throws light on purely organic mate-
tion for their application in optoelectronic devices such as rials based luminophors and their use in optoelectronics [4–9].
organic solar cells, organic light emitting diodes (OLEDs), But many of the methods used by researchers in organic syn-
organic photovoltaic devices, etc. [1–3]. Furthermore, demand thesis are very tedious, time consuming and need expensive
from optoelectronic industries for these materials encouraged catalysts [10]. Vapour phase method, crystal growth method
researchers to go for it. As compared to the metals doped in from solution, melt growth method and solid state growth
inorganic materials, organic doped materials find greater ap- method by heating have also been employed for the same
plications in LEDs with respect to effortless synthesis, reason- purpose [11, 12]. Amongst which, doping technique turns
able, lightweight property, flexibility, etc. and embrace a pro- efficient method named as conventional solid state reaction
ductive field. These crucial facts encouraged their applications technique to get the emission of fluorescent materials due to
its simple processing, informal heating and proficient output
with great purity materials [13]. In conventional solid state
* K. G. Mane reaction technique, selection of host and guest materials play
kanchanmane13@gmail.com a dynamic role. Intermolecular energy transfer in between host
and guest is considered because of intramolecular interactions
P. B. Nagore
pravin.nagore@gmail.com
[14, 15]. In present article, monoclinic host material has been
chosen and purposely doped with blue light emitting guest as
S. R. Pujari an effective donor of excitation energy with the D-type (dif-
pujari_aarush@yahoo.co.in
fusion spectrum) crystal lattice which trap the excitation ener-
1
Doshi Vakil Arts & G.C.U.B. Sci. & Comm. College, Goregaon, gy of host and attain alteration in the fluorescence spectrum of
Raigad 402103, Maharashtra, India the host material [16-19]. Hence, in this study, 2-naphthol is
2
D.B.F.Dayanand Science College, Solapur, Maharashtra, India preferred as a host material which solubilize anthracene as a
 J Fluoresc

guest material and transfer electronic excitation energy to the Preparation of Doped 2-Naphthol Luminophors
guest molecules via EET process, because of two benzene
rings of 2-naphthol which are not co-planar in ground state The conventional solid-state reaction technique was employed
but oriented in the plane in an electronically excited state by to prepare polycrystalline luminophors of 2-NP containing
absorbing UV radiations. Aim of current article is to improve AN [20, 21]. Different concentrations of AN doped 2-NP
emission of 2-naphthol by integrating selected dopant with solid solutions were formed by mixing appropriate amount
different concentrations and to make it applicable for opto- of these two in silica crucible with heating at the temperature
electronic devices. just above the melting point of 2-NP(122 °C). Then the ob-
tained melt was cooled slowly to get polycrystalline
luminophors of AN doped 2-NP with fine crushed powder.
Finally, the fine powder of doped 2-NP was used to study the
Experimental photophysical, thermal and electrochemical properties.

Pure 2-naphthol and anthracene of scintillation grade were Characterization Techniques

procured from Merck-Schuchardt. The same were recrystal-
lized and purified by the sublimation method. The similarity The fluorescence spectra of doped 2-naphthol was recorded
in the fluorescence spectra at different excited wavelength in by JOBIN YVON Fluorolog-3-11 spectrofluorimeter, at IIT
the UV region confirmed the purity of these substances. Madras. The XRD analysis of doped and undoped crystals

Fig. 1 XRD study of pure 2-NP 400000

and AN doped 2-NP. a 1 × 10−3
M, b 1 × 10−2 M, c 1 × 10−1 M of 300000
Intensity

Pure AN
AN per mole 2-NP and e pure AN 200000

100000

0
0 10 20 30 40 50 60 70

120000
100000
80000 1 x 10-1 AN doped 2-NP
Intensity

60000
40000
20000
0
0 10 20 30 40 50 60 70

80000
60000
Intensity

1 x 10-2 AN doped 2-NP

40000
20000
0
0 10 20 30 40 50 60 70

150000
Intensity

100000
1 x 10-3 AN doped 2-NP
50000

0
0 10 20 30 40 50 60 70

120000
100000
Intensity

80000
60000
Pure 2-naphthol
40000
20000
0
0 10 20 30 40 50 60 70
2ϴ
J Fluoresc

Table 1 Structural parameters of

2-naphthol luminophors Conc. of AN,(M) Pure AN 1 × 10−3 1 × 10−2 1 × 10−1 Pure 2-NP
Per mole of 2-NP

Glancing Angle, (2θ) degree 9.550 19.510 19.170 19.460 19.445

FWHM, β2θ 0.471 0.447 0.424 0.482 0.446
Microstain, ɛ × 10−3 l2/m−4 2.047 1.921 1.824 2.072 1.917
GrainSize, (D) A0 428.9 267.1 281.4 247.8 266.9
Dislocation Density, ρ × 1015 cm−2 3.129 4.730 4.264 5.501 4.725
Stacking Fault 0.4122 0.2727 0.2587 0.2945 0.2725

was carried out by Philips Diffractometer (PW-3710 model, concentration. On doping of a pure crystal into host, it deforms
Holland) with CrKα radiation (2.28 Ǻ). (TGDTA-DSC) TA by producing defects and imperfection into host lattice. Hence,
Inc. SDT- 2790 with heating rate 10 °C per minute under the this deformation changes microstrain marginally and disloca-
nitrogen atmosphere was employed to carry out tion density as per the expectation [23]. It has been calculated
Thermogravimetric analysis, while FEI Quanta FEG 200 - and tabulated in (Table 1). Also Stacking fault observed to be
Scanning Electron Microscope was used to study surface mor- improved with guest anthracene in 2-naphthol host material.
phology of samples. This result concluded to consider close packed structure of both
host and guest molecules. SEM micrographs (Fig. 2) of doped
and undoped 2-naphthol exhibits well separated, identical crys-
Results and Discussion tallites of monoclinic form. Also, SEM micrographs noted av-
erage crystallite size of 133 nm which is the range desired in
Structural Studies of Doped 2-Naphthol Luminophors optoelectronic devices.
by XRD
Photophysical Properties
X-ray diffraction spectra of pure and anthracene doped 2-
naphthol is shown in Fig. 1. XRD profile of fine grained pow- 2-naphthol which is monoclinic unit cell when excited at
der exhibited sharp peaks which specify crystallinity and ho- 330 nm radiation exhibits fluorescence in the UV region
mogeneity of the doped luminophors. No additional peak for [24]. Anthracene is well identified for it's emission like naph-
AN was observed in the spectrum of 2-NP luminophors. This thalene matrix by EET process.
reflection specify that, the mixed crystals of two components The fluorescence spectrum of 2-NP and AN doped 2-NP
are homogenous. Along with this, the structural parameters like are shown in Fig. 3. It has been observed that, fluorescence
microstrain, dislocation density, grain size and stacking fault spectra of anthracene doped 2-naphthol is structured and ap-
were also calculated and tabulated in (Table 1). Classical pears to be blue shifted viz. 413 nm which differ completely
Sherrer formula has been used to estimate the average grain from fluorescence spectrum of 2-naphthol. The absence of 2-
size of 2-naphthol luminophors [22]. The addition of AN as a naphthol emission bands clearly specify that the excitation
guest material into 2-NP showed highest grain size for 1 × 10−2 energy of 2-naphthol exciton is trapped by anthracene due to

Fig. 2 SEM images of a pure AN

and b 1 × 10−1 M of AN per mole a b
2-NP
 J Fluoresc

Fig. 3 a Fluorescence spectra of 25000000

pure 2-NP and 1x10-1,1x10-
2,1x10-3AN doped 2-NP b 20000000
Fluorescence spectra of pure 2-

Intensity(a.u.)
NP and 1x10-1,1x10-2,1x10-
15000000 1x10-1 anth/mole 2-naphthol
3,3x10-3,7x10-3,2x10-1AN
doped 2-NP c Fluorescence spec- 1x10-2 anth/mole 2-naphthol
tra of thin film AN doped 2-NP 10000000
1x10-3 anth/mole 2-naphthol

5000000 emission of 2-napthol

0
350 400 450 500 550 600
Wavelength
a
25000000

20000000 1x10-1 anth/mole 2-naphthol

Intensity(a.u.)

1x10-2 anth/mole 2-naphthol

15000000
1x10-3 anth/mole 2-naphthol
10000000
3x10-3 anth/mole 2-naphthol
5000000 7x10-3 anth/mole 2-naphthol
0 2x10-1 anth/mole 2-naphthol
350 400 450 500 550 600 emission of 2-napthol
Wavelength in nm

b
400000
350000
300000
Intensity(a.u)

250000
200000 1x10-1
150000 1x10-2
100000 1x 10-3
50000
0
310 360 410 460 510 560
Wavelength (nm)

excitation energy transfer (EET) with immediate fluorescence 413 nm. As the concentration of anthracene increased, peak
quenching of 2-NP. Hence, for 1 × 10−3 and 1 × 10−2 anthra- shift towards longer wavelength with increase in intensity of
cene doped 2-naphthol, the peak appeared at 412 nm and peak.

Table 2 Emission data of solid

material and their thin films with Compounds λemi(a),nm λemi(b), nm of thin Films EgOpt (c) (eV)
optical band gap of doped 2-NP
luminophors 1 × 10−1AN/mol 2-NP 421 420 2.94,(2.95)
1 × 10−2AN/mol 2-NP 415 413 2.98,(3.00)
1 × 10−3AN/mol 2-NP 415 414 2.98,(2.99)
3 × 10−3AN/mol 2-NP 415 – 2.98,(−)
7 × 10−3AN/mol 2-NP 414 – 2.99,(−)
2 × 10−1AN/mol 2-NP 420 – 2.95,(−)
a
Recorded, b Recorded,, c (EgOpt = 1240.8/λ opt edge)eV,
J Fluoresc

Also the fluorescence study of thin films of anthracene 1

doped 2-naphthol by employing spin coating technique was
carried out as shown in Fig. 3c and result listed in Table 2. The
0
results fulfilled our expectations.

Mass percentage
Thermal Properties of Doped 2-Naphthol -1

Luminophors
-2
To exhibit optical applications, materials need to be thermally
stable. To examine alteration in thermal properties of 2- -3
naphthol doped anthracene, thermogravimetric analysis has
been done. Figures 4 and 5 show TGA and DSC thermo-
-4
graphs of 2-naphthol doped anthracene under the nitrogen
atmosphere within temperature range of 0–300 °C. From 0 50 100 150 200 250 300
Fig. 4, it is observed that, the anthracene doped 2-naphthol 0
Temperature( C)
remains thermally stable up to 125 °C and after that the de-
Fig. 5 DSC curve of 2-naphthol containing anthracene
composition starts. The complete process of decomposition
proceeds in three stages. The stage one from 125 °C to
230 °C, the stage two from 230 °C to 250 °C in which max-
imum weight loss is observed while decomposition of remain- which may be due to two electron process in anthracene im-
ing compound indicate weight loss in third stage. The Fig. 5 purity doped in 2-naphthol (Fig. 6). For the synthesized
show DSC curve which exhibits one endothermic peak at luminophors the HOMO and LUMO energy levels were ob-
120 °C. served in the range of 5.55–5.71 eV and 3.03–3.24 eV respec-
From thermogram it is clear that doped 2-naphthol is suit- tively. The Eg calculated from the CV were in the range of
able for device fabrication and to facilitate an enhanced life- 2.25–2.82 eV which found in close proximity with optical
time of the devices. band gap [25, 26]. Thus, the prepared luminophors are good
applicants as n-type materials used in optoelectronic devices.
Electrochemical Properties The observed parameters are tabulated in Table 3.

Electrochemical properties of AN doped 2-NP luminophors

were studied by Cyclic Voltammetry technique (CV) in di- Conclusion
chloromethane solution using ferrocene as an internal
standard.On anodic sweep, two quasi-reversible waves were The structural, emission, electrochemical and thermal proper-
observed near-0.2 and near 0.4 in the first and third curve ties of the synthesized luminophors are significantly influ-
enced by the concentration of guest material with emission

100
1
0.020 2
3
80
0.015
Mass percentage

60 0.010

0.005
40
i/A

0.000

20 -0.005

-0.010
0
-0.015

0 50 100 150 200 250 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0
0
Temperature( C) E/V

Fig. 4 TGA curve of 2-naphthol containing anthracene Fig. 6 Cyclic voltammogram of 2-NP doped AN
 J Fluoresc

Table 3 Electrochemical data of

doped 2-NP luminophors Compound EOxpeak(a) ERedpeak(b) HOMO(c) LUMO(d) Eg(e)

1) 1 × 10−1AN/mol 2-NP 0.71 −0.53 −5.71 −3.24 2.74

2) 1 × 10−2AN/mol 2-NP 0.52 −0.74 −5.52 −3.03 2.49
3) 1 × 10−3AN/mol 2-NP 0.55 −0.68 −5.55 −3.09 2.46

{a EOxpeak Oxidation peak potential(V), b ERedpeak Reduction peak potential(V), c HOMO,EHOMO = −(EOxpeak -
EOx (Fc/Fc+ ) + 4.8)eV, d LUMO,ELUMO = −(ERedpeak - ERed (Fc/Fc+) + 4.8)eV, Eg(e) = EHOMO – ELOMO}27

at blue region. The electrochemical and thermal study of the physical vapor transport: towards high-quality and color-tunable
crystal preparation. Cryst Eng Comm 16:4539–4545
synthesized luminophors confirmed their use as n-type mate-
12. Ravi G, Srinivasan K, Anbukumar S, Ramasamy P (1994) Growth
rial for Optoelectronic devices. and characterization of sulphate mixed L-arginine phosphate and
ammonium dihydrogen phosphate/potassium dihydrogen phos-
Acknowledgements The authors express sincere thanks to IIT Madras, phate mixed crystals. J Cryst Growth 137:598–604
SAIF and Instrumentation Centre, Solapur University, Solapur, 13. Desai NK, Kolekar GB, Patil SR (2012) Preparation and character-
Maharashtra-India and D.B.F. Dayanand College of Science, Solapur, ization of anthracene doped p-terphenyl polycrystalline powders for
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