Supporting Information
Concurrent tuning of trap distribution and crystal field in
Cr3+-doped non-gallate phosphors with the near-infrared long
persistent phosphorescence
Yang Lia,b,c, Yiyang Lid, Ruchun Chena, Kaniyarakkal Sharafudeene, Shifeng Zhoua,b,
Mindaugas Geceviciusf, Haihui Wang c, Guoping Donga,b, Yiling Wua,b, Xixi Qina,b, and
Jianrong Qiu* a,b
a
State Key Laboratory of Luminescent Materials and Devices , School of Materials
Science and Technology, South China University of Technology, Guangzhou 510640,
China
b
Guangdong Provincial Key Laboratory of Fiber Laser Materials and Applied
Techniques, Guangzhou 510640, China
c
School of Chemistry and Chemical Engineering, South China University of Technology,
Guangzhou 510640, China
d Henry
Samueli School of Engineering, University of California, Irvine, CA
92697-2575,USA
e Escola
de Engenharia de Sao Carlos, Universidade de Sao Paulo, 13566-590, Sao
Carlos, SP, Brazil
f
Optoelectronics Research Centre, University of Southampton, SO17 1BJ, United
Kingdom
*Corresponding authors:
Tel: +86-20-87113646
Fax: +86-20-87114204
Structure properties
XRD patterns of Zn2-xAl2xSn1-xO4 system were measured as shown in Figure s2.
These results reveal the existence of Zn2-xAl2xSn1-xO4 system i.e., a solid solution
between the ZnAl2O4 and Zn2SnO4 crystal structures. When x≤0.2 (samples ZS3-ZS9),
we have synthesized the pure Zn2SnO4 inverse spinel compounds (JCPDS 24-1470).
But in fact, we believe this Zn1.8Al0.4Sn0.8O4 compound is a solid solution including Al.
To further identify the composition of the as-prepared Zn1.8Al0.4Sn0.8O4 solid solution,
the analysis of X-ray photoelectron spectra (XPS) was carried out as shown in Figure
s111. Except the obvious XPS signal of O 1s at 529eV, Zn 2p3/2 at 1019.7eV and Sn 3d5/2
at 484.5eV, the strong Al 2p3/2 signal in XPS spectra of the as-prepared phosphor was
also detected at 72eV, meaning that the novel bond formed. The Al 2p3/2 peaks can be
used as a sensitive tool to identify the efficient substitution of Al3+ and the formation
of znic aluminostannate solid solution. Interestingly, with the increment of Al content,
all XRD peaks of Zn2SnO4 crystal structure in samples ZS3-ZS9 shift toward higher 2θ
values, because the ion radius of Al3+ (0.053nm) is smaller than that of Zn2+ (0.074nm)
and Sn4+ (0.0069nm). Based on the Bragg's law, d (the spacing between the planes in
the atomic lattice) is inversely proportional to θ (the angle between the incident ray
and the scattering planes). Owing to the shortening of the distances among the
ligands (AlO6, ZnO6, SnO6), the crystal field strength of Cr3+ will increase in consistent
with the analysis for the absorption/excitation spectra. As a result, the energy level
splitting increases, resulting in the blue-shift of emission waveband and the upward
shift of conduction band. ZnAl2O4 secondary phase (JCPDS 82-1043) is found to be
present in the phosphor for x≥0.2 (ZS10). When the doping dose of Al content is
beyond 0.4 and even reaches to 0.8 (ZS11), the Zn2SnO4 inverse spinel disappears and
only the ZnAl2O4 phase remains; at the same time, the persistent phosphorescence
also begins to weaken until to disappear. Thus, the interaction of the variation of
crystalline structure with both the persistent duration and emission band is
substantiated.
Band gap evaluation
In order to evaluate the optical band gap, the (hυα)2–hυ curves of non-doped
Zn2SnO4 (ZS12) and Zn1.8Sn0.8Al0.4O4 (ZS13) were plotted according to an expression
proposed by Tauc2:
(hν*α)2  A *(hν  E)
(1)
The values of the band-gap energy can be read from the intercepts of fitted straight
lines. The results were shown in Figure s6 (ZS12, 3.78 eV; ZS13, 4.21 eV).
Figures
Figure s1. (a) Cubic inverse spinel structure of Zn2SnO4; (b) Rhombohedral phenakite
structure of Zn2GeO4; (c) Willemite structure of Zn2SiO4.
Figure s2. (a-c) XRD patterns of all the samples (ZS1, ZG2, ZS3-ZS11); (d) XRD peak (I)
position as a function of Al doping content
Figure s3. Home-made device used to record the absolute afterglow intensity. An
optical power meter (Thorlabs PM320E), and a PMT power sensor (Thorlabs S120C,
50 nW-50 mw, aperture size is Ø 9.5 mm, wavelength range is 400-1100 nm) were
used as the signal collector.
Figure s4. (a) Normalized long persistent phosphorescence spectra as a function of Al
concentration. The measurements were taken at 1 min after the stoppage of
irradiation; (b)-(d) Dependence of emission peak positions ([I] [II] and [III] labeled in
Figure s4a) and (e) intensity ratio of the emission peaks [III]/[I] as a function of Al
concentration.
Figure s5. Absolute (a) and relative (b) afterglow intensities of sample ZS9 (1g)
monitored at 722 nm as a function of time. The sample was pre-irradiated by a xenon
lamp for 30 min before the measurements.
Figure s6. Normalized thermo-luminescence curve of the sample ZS11 measured at
30 s after the stoppage of irradiation.
Figure s7. Diffuse reflection spectra of samples ZS12 and ZS13.
Figure s8. Normalized thermoluminescence excitation spectrum of sample ZS3. It is
obtained by integration of the TL glow between 300 and 400 K.
Figure s9. Thermo-luminescence curves of the samples ZS3-ZS10 measured at 24
hours after the stoppage of irradiation.
Figure s10. Afterglow intensities of sample ZS9 monitored at 722 nm (a) and sample
ZS3 monitored at 800 nm (b), ESR signal intensities with g=3.93 of sample ZS9 (c) and
g=1.99 of sample ZS3 as a function of time (at 1 min, 1 h, 6 h, 12 h, 24 h after the
stoppage of irradiation).
Figure s11. XPS spectra of the as-prepared Zn1.8Al0.4Sn0.8nO4: 0.2% Cr3+ solid solution:
(a) Zn 2p, (b) Al 2p, (c) O 1s, and (d) Sn 3d.
References
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2. Zhuang, Y. X., Ueda, J., Tanabe, S. & Dorenbos, P. Band-gap variation and a
self-redox effect inducedby compositional deviation in Zn xGa2O3+x: Cr3+ persistent
phosphors. J. Mater. Chem. C 2. 5502-5509 (2014).