Materials Letters 63 (2009) 2600–2602
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Materials Letters
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / m a t l e t
Synthesis and calcination temperature dependent photoluminescence properties of
novel bromosilicate phosphors
Zhiguo Xia ⁎, Guowu Li, Daimei Chen, Haiyi Xiao
School of Materials Sciences and Technology, China University of Geosciences, Beijing 100083, PR China
a r t i c l e
i n f o
Article history:
Received 18 June 2009
Accepted 4 September 2009
Available online 12 September 2009
Keywords:
A. Optical materials
D. Luminescence
D. Optical properties
a b s t r a c t
Novel Eu2+-doped bromosilicate phosphors, (CaO–CaBr2–SiO2):0.03Eu2+, were prepared by the traditional
solid-state method under a different calcination temperature. The as-prepared (CaO–CaBr2–SiO2):0.03Eu2+
phosphors obtained under various reaction temperatures all indicated a broad excitation in the near
ultraviolet region (350–450 nm). The phosphor system exhibits bluish-green light with a peak wavelength at
498 nm when the calcination temperature is below 800 °C, while it shows a strong blue emission light with a
peak wavelength at 474 nm as the calcination temperature is above 800 °C, and it also gives an interesting
greenish-yellow long-lasting phosphorescence with a peak wavelength at 540 nm in the dark.
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
In the past decade, significant research efforts have been devoted to
achieve novel material systems with excellent photoluminescence
properties for illumination and display applications [1,2]. Silicates are
one of the largest classes of compounds in inorganic chemistry, which
are of special interest to us as host lattices for rare-earth-doped
phosphors [3,4]. Among them, the studies on halosilicate materials, such
as flurosilicate, chlorsilicate and bromosilicate matrix, have attracted
more and more attention [5–9]. In recent years, the studies on Eu2+doped halosilicate-based phosphors, such as Ca3SiO4Cl2:Eu2+ [7], and
Ca10(Si2O7)3Cl2:Eu2+ [8], Ba5SiO4(F,Cl)6:Eu2+ [9] have become a hot
issue in exploring new phosphor materials, which have also been
proven to be efficient in the application of the white LEDs' lightconversion phosphors.
In our previous work, the peculiar long-lasting phosphorescent
luminescent properties in the (CaO–CaBr2–SiO2) phosphor system
have been studied [10]. In this paper, the synthesis and optical
properties of (CaO–CaBr2–SiO2):0.03Eu2+ phosphor were studied as a
function of calcination temperature, which was also investigated to
develop new materials with potential application for white LEDs.
2. Experimental
The chemical composition of the Eu2+-doped (CaO–CaBr2–SiO2)
phosphor system is given by means of the imaginary formula
‘Ca3SiO4Br2:Eu2+’. The phosphor samples were synthesized by the
⁎ Corresponding author. Tel: + 86 1 0 8232 2759.
E-mail address: [email protected] (Z. Xia).
0167-577X/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.matlet.2009.09.017
high-temperature solid-state synthesis method. The starting materials,
Ca(OH)2 (A.R.), CaBr2·2H2O (A.R.) and SiO2 (A.R.) were weighted by a
molar ratio of Ca(OH)2, CaBr2∙2H2O and SiO2 = 2:1∙1:1. According to our
former reported data [10], an optimum mole amount of Eu2O3
(0.03 mol) was added in the mixture as the activator. The mixed
samples were fired for 3 h at the selected temperature, 700 °C, 800 °C,
900 °C and 1000 °C in CO reducing atmosphere, and highly pure carbon
grains were used as a reducing agent, by which the samples were
covered during firing. X-ray diffraction (XRD) patterns were recorded
by using an X-ray powder diffractometer (SHIMADZU, XRD-6000)
operating at 40 kV, 30 mA and a scanning speed of 2.0° (2θ)/min, using
monochromatized Cu Kα radiation. Diffuse reflection spectra of assynthesized phosphor powder samples were measured on a UV–vis–
NIR spectrophotometer (UV-3600, SHIMADZU) attached to an integral
sphere. BaSO4 was used as a reference standard. The photoluminescence
(PL) spectra were recorded by using a Perkin-Elmer LS-55 fluorescence
spectrophotometer with a photomultiplier tube operating at 400 V, and
a 150-W Xe lamp was used as the excitation lamp.
3. Results and discussions
Fig. 1 gives the XRD patterns of (CaO–CaBr2–SiO2):0.03Eu2+
phosphors for various calcination temperatures. As shown in Fig. 1,
the obtained diffraction peaks of Eu2+-doped CaO–CaBr2–SiO2
phosphor systems synthesized at four different temperature conditions do not match any data in the JCPDS base after careful
comparison. However, we also find that there are two kinds of
diffraction peaks, which correspond to the two possible structural
phases. The products obtained at 700 °C and 800 °C belong to the
same series, while the products obtained at 900 °C and 1000 °C are the
other types from the given diffraction data in Fig. 1. Hereafter, we
denote them as L-phase for the (CaO–CaBr 2 –SiO 2 ):0.03Eu 2+
Z. Xia et al. / Materials Letters 63 (2009) 2600–2602
Fig. 1. XRD patterns of (CaO–CaBr2–SiO2):0.03Eu2+ phosphor for various calcination
temperatures: (a) 700 °C, (b) 800 °C, (c) 900 °C, and (d) 1000 °C.
phosphors synthesized at 700 °C and 800 °C, and H-phase for those
synthesized at 900 °C and 1000 °C.
The UV–vis diffuse reflection spectra of (CaO–CaBr2–SiO2):0.03Eu2+
phosphors for various calcination temperatures are given in Fig. 2. There
are two obvious absorption bands, 230–310 nm and 320–480 nm,
attributed to transition from 4f 7 to 4f 65d1 of Eu2+ ions [11]. As the
calcination temperature increases, the absorption intensity of an
absorption band ranging from 320 nm to 480 nm increases. Another
important difference lies in that it can be divided into two series
absorption profiles. It testifies that there are two kinds of crystal phases
in the (CaO–CaBr2–SiO2):0.03Eu2+ phosphor systems, and it also reflects
that a different host system will bring about a different UV–vis diffuse
reflection spectra characteristic. The inset in Fig. 2 gives the comparison
of UV–vis diffuse spectra of (CaO–CaBr2–SiO2) host and 0.03Eu2+-doped
(CaO–CaBr2–SiO2) system synthesized at 900 ºC. It is observed that the
(CaO–CaBr2–SiO2) host shows a platform of high reflection in the
wavelength range of 400–800 nm and then starts to decrease slightly
from 400 to 200 nm, due to the host absorption. It is found that the
absorption band of the Eu2+ doped (CaO–CaBr2–SiO2) system is
different to the host absorption with two obvious absorption bands in
the near-UV region, thereby (CaO–CaBr2–SiO2) host can't be efficiently
excited by the near-UV light owing to the absence of Eu2+ ions.
Fig. 2. UV–vis diffuse reflection spectra of (CaO–CaBr2–SiO2):0.03Eu2+ phosphor for
various calcination temperatures: (a) 700 °C, (b) 800 °C, (c) 900 °C, and (d) 1000 °C;
and the inset shows the comparison of the UV–vis diffuse spectra of (CaO–CaBr2–SiO2)
host and the 0.03Eu2+-doped (CaO–CaBr2–SiO2) system synthesized at 900 °C.
2601
Fig. 3. Emission spectra (1) and excitation spectra (2) of (CaO–CaBr2–SiO2):0.03Eu2+
phosphor for various calcination temperature: (a) 700 °C, (b) 800 °C, (c) 900 °C, and
(d) 1000 °C.
Fig. 3 shows the excitation spectra and emission spectra of (CaO–
CaBr2–SiO2):0.03Eu2+ phosphors for a different calcination temperature. As seen in Fig. 3 (1)a–b, L-phase (CaO–CaBr2–SiO2):0.03Eu2+
phosphor shows an intense bluish-green broad emission around
497 nm upon 420 nm excitation. Monitoring the bluish-green emission
at 497 nm, there are several broad excitation bands around 311, 360,
393, 421 and 445 nm, as seen in Fig. 3 (2). In contrast, as shown in
Fig. 3 (1)c–d, H-phase (CaO–CaBr2–SiO2):0.03Eu2+ phosphor shows a
strong blue broad emission around 474 nm upon 420 nm excitation. It is
also observed in Fig. 3 (2) that the excitation spectra of H-phase consist
of four broad bands around 313, 362, 394 and 420 nm. As is known, the
broad excitation profiles are mainly due to transition of Eu2+ from 4f
ground state to 5d excited state, which also agree with the UV–vis
diffuse reflection spectra [12]. However, the complicated structure of
the excitation spectra of Eu2+ ion indicates that the site occupied by
the Eu2+ ion has a lower symmetry [13]. It is found that both L-phase
and H-phase have a similar excitation character, except for the 445 nm
excitation band belonging to the L-phase. However, two different
structure phases in the (CaO–CaBr2–SiO2) system can also be found, and
Fig. 4. Comparison of the normalized emission spectra of L-phase (a) and H-phase (b) upon
365 nm UV excitation, and afterglow spectrum of H-phase (c) of (CaO–CaBr2–SiO2):0.03Eu2+
phosphor. Inset: digital photographs of the photoluminescence and phosphorescence for the
corresponding phosphors.
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Z. Xia et al. / Materials Letters 63 (2009) 2600–2602
H-phase should be a stable structure and has higher symmetry
compared to L-phase.
It is also found that, if the reaction temperature is above 850 °C,
(CaO–CaBr2–SiO2):0.03Eu2+ phosphor system can show greenishyellow light-emitting, long-lasting phosphorescence, except for the
blue emission under near-UV excitation [10]. Fig. 4 shows the
comparison of the normalized emission spectra of L-phase (a) and Hphase (b) upon 365 nm UV excitation, and afterglow spectrum of Hphase (c) for the (CaO–CaBr2–SiO2):0.03Eu2+ phosphor, and their
respective digital photographs are also given in the inset of Fig. 4. It is
obvious that the three emission spectra are all asymmetric in the spectra
profiles. As marked by a solid arrow at 498 nm, 474 nm and 540 nm in
Fig. 4, it indicates that, the PL spectrum of L-phase exhibits a clear bluishgreen color with peak wavelength at 498 nm, the PL spectrum of Hphase gives a clear blue color with a peak wavelength at 474 nm, while
the LLP spectrum of H-phase shows a greenish-yellow color with the
main peak wavelength at 540 nm, as also shown by their respective
digital photographs.
4. Conclusions
The interesting calcination temperature dependence bluish-green
and blue emission phosphors, which is based on the same Eu2+-doped
bromosilicate phosphor systems, (CaO–CaBr2–SiO2):0.03Eu2+, were
prepared by the traditional solid-state method. Under 420-nm near-UV
light, L-phase phosphor exhibits a bluish-green light with a peak
wavelength at 498 nm, while H-phase phosphor shows strong blue
emission light with a peak wavelength at 474 nm. The peculiar longlasting phosphorescence property belonging to the H-phase was also
found. The present photoluminescent property results indicate that the
(CaO–CaBr2–SiO2):0.03Eu2+ phosphors prepared by a different reaction
temperature are promising to meet the application requirements for
near-UV GaN-based light-emitting diodes (LEDs) as blue or greenemitting phosphors owing to their broad excitation in the near
ultraviolet region (350–450 nm).
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