Far-Red-Emitting BiOCl:Eu3+ Phosphor with Excellent Broadband
NUV-Excitation for White Light-Emitting Diodes
Yongjin Li1,2, Zongyan Zhao1, Zhiguo Song1*, Ronghua Wan1, Jianbei Qiu1*,
Zhengwen Yang1, Zhaoyi Yin1, Xuee Liu1, Qun Liu1, Yuting Zhou1
1
School of Materials Science and Engineering, Kunming University of Science and
Technology, Kunming, 650093, China
2
Department of Science Research, Yunnan Technology and Business University,
Kunming, 651700, China

Corresponding Author: E-mail: songzg@kmust.edu.cn
Electronic Supporting Information
Figure S1. The main diffraction peak near 2θ = 35º with different Eu3+ ion
concentrations.
S1
Table S1 Cell constants a, b, c, and cell volume (V) of Eu3+-doped BiOCl with
different Eu3+ ions concentration
Eu3+ concentration
(mol%)
Lattice constant(Å)
a=b
c
V
(Å3)
0
3.898
7.379
112.12
1
3.893
7.356
111.51
3
3.892
7.362
111.52
5
3.891
7.364
111.46
7
3.890
7.350
111.23
10
3.887
7.343
110.96
From the Figure S1, it is noteworthy that the diffraction peaks are shifted to a
high 2θ angle with increases Eu3+ ions concentrations, implying that the Eu3+ ions
have been doped into the lattices of BiOCl. On the other hand, the diffraction peaks
get broadened as the Eu3+ concentration is increased, suggesting a systematic decrease
in the grain size. The peaks which correspond to the crystal planes (001) and (110) of
the tetragonal phase are selected to calculate the lattice parameters of the Eu3+-doped
BiOCl phosphors. Using the Equation S-1, the lattice parameter and unit cell volume
of the samples were evaluated (Table S1).
1/d2 = (h2+k2)/a2 + l2/c2
(S-1)
Here, h k l are the Miller indices; a, b, and c are the lattice parameters (in a tetragonal
system, a = b ≠ c); d is the interplanar spacing between the crystal planes (hkl). As
can be seen from the estimated data, the estimated lattice parameters and unit cell
volume values for the Eu3+ doped BiOCl deviate considerably from those of the
un-doped BiOCl due to the incorporation of Eu3+ ions into the BiOCl lattice. Because
S2
the radius of Eu3+ is smaller than that of Bi3+, the lattice constants become smaller
while Eu3+ substitutes Bi3+.
Figure S2. Diffuse reflectance spectra of Eu3+-doped BiOCl phosphor with different
Eu3+ ion concentrations.
Band gap energy of samples according to the diffuse reflectance spectra
It was reported that the absorption coefficient (α) of a semiconductor and its
band gap energy (Egap) are related through the following equation:1,2
αhv = (hvEgap)n
(S-2)
where h is Planck’s constant, v is the frequency of the light, and n is a constant
depending on the transition type, which can be 1/2, 3/2, or 2 corresponding to direct
allowed, direct forbidden, or indirect transition, respectively. In our cases, BiOCl has
been confirmed to be indirect materials; thus, n = 2. According to the Kubelka-Munk
equation:1
F(R∞) = (1 R∞)2/2 R∞ = k/s
(S-3)
where R∞ is the diffuse reflectance of the layer relative to the standard, k is the molar
S3
absorption coefficient of the sample, and s is the scattering coefficient. Function F(R∞)
can be obtained from the DR spectra shown in Figure 3(a) and Figure S2. For a given
material, s is independent of the wavelength of the incident light, and k is proportional
to the  in Eq. S-2. As a result, F(R∞) is proportional to the absorption coefficient α;
substituting α with F(R∞) in Eq. S-2, we obtain
hvF(R∞) (hv Egap)
(S-4)
By plotting [hvF(R∞)]1/2 ∼hv in panels (b) and (c) of Figure 3, we determined the band
gap energies of un-doped BiOCl and 0.07Eu3+ -doped BiOCl to be 3.33 and 2.81 eV,
respectively. Additionally, as for samples doped with 0.01, 0.03, 0.05, and 0.1 Eu3+,
by the same method, the band gap energies are 3.21, 3.07, 2.98, and 2.71,
respectively.
Figure S3. (a) Excitation spectrum of Eu3+ (7 mol%)-doped BiOBr phosphor
recorded at λem= 622 nm; (b) Diffuse reflectance spectra of Eu3+ (7 mol%)-doped
BiOBr phosphor.
S4
Figure S4. Emission spectra of Eu3+ (7 mol%)-doped BiOCl phosphor exciting at 466
nm.
Theoretical calculation of charge transfer (CT)
Method 1:
The charge transfer excitation of Eu3+ is an electronic transition from the
ground-state to the excited-state of the 4f shell, and the corresponding band position
in excitation spectrum is mainly determined by the covalency of Eu-O bond and the
coordination environment of Eu3+ as well. As usual, an increase in covalency of Eu-O
bond would reduce the energy for electron transfer. In the Eu-O couple, the excitation
energy for charge transfer can be estimated by the following Jorgensen’s equation,3
ν=3[χ(O)- χ(Eu)] × 104
(S-5)
where ν in cm-1 denotes the position of the charge transfer band, χ(O) and χ(Eu) are
the optical electronegativity of the oxygen and europium ions, respectively. Taking
χ(O)= 3.2 and χ(Eu) =1.75, the band position for Eu-O charge transfer is calculated to
be at 230 nm (or 43500 cm-1) in BiOCl.
S5
Method 2:
According to the equation:4
ECT = 2.542 + 0.171 ×Eμg
(S-6)
where ECT is CT energy, and Eμg is average energy gap for any μ bond in units of
electron volts (eV). Because YOCl, LaOCl and BiOCl all have tetragonal PbFCl-type
structure (space group P4/nmm; No. 129), moreover, the radius is Y3+< Bi3+< La3+.
Therefore, we reason that Eμg of BiOCl (Bi-Cl) is between YOCl (Y-Cl) and LaOCl
(La-Cl). According to Ref. 5 and Eq.S-6, the ECT of YOCl and LaOCl is 4.40 and 4.28
eV, respectively. So the ECT of BiOCl is about 4.3 eV (about 288 nm) in BiOCl. With
the same method, the ECT is calculated to be about 4.1 eV (about 300 nm) in BiOBr.
According to the above result, we reason that broad NUV excitation band is
assigned to the band gap of BiOCl rather than the CT of Eu3+-O2-.
Figure S5. Emission spectra of Eu3+ (7 mol%)-doped BiOCl phosphor exciting at 358
nm with Hitachi F-7000 Fluorescence Spectrophotometer.
S6
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