Supporting Information
Evolution in the Oxidation Valences and Sensitization Effect of Copper through
Modifying Glass Structure and Sn2+/Si Co-Doping
Tian-Shuai Lv †, Xu-Hui Xu *,†, Xue Yu †, and Jian-Bei Qiu *,†
†
School of Materials Science and Engineering, Kunming University of Science and
Technology, Xuefu RD, Kunming 650093, PR China
*Corresponding author: qiu@kmust.edu.cn (J.-B. Qiu), xuxuh07@126.com (X.-Xu. Xu)
Experimental Synthesis
High-purity B2O3 (99.99%), Li2CO3 (99.99%), Al2O3 (99.99%), CaCO3 (99.99%), Cu2O (99.9%),
TbF3 (99.99%), SnO (99.9%), and Si powder (5N) were employed as the raw chemicals, which were
first mixed homogeneously with a pestle and agate mortar, and then melted at 1250 oC for 25 min
under an ambient atmosphere. The glass melts were cast onto a stainless-steel mold maintained at 300
oC,
and then annealed at 400 oC for 2 h to relieve the internal stress. The as-prepared samples were
mechanically polished into mirror surfaces with mixed aqueous diamond slurries before subjecting to
subsequent measurements.
Measurements and Characterization.
Absorption (ABS) and transmittance (TRA) spectra were recorded on a HITACHI U-4100
spectrophotometer with a PMT voltage of 400 V. The photoluminescence excitation (PLE) and
photoluminescence
(PL)
spectra
were
performed
on
a
HITACHI
F-7000
fluorescence
spectrophotometer equipped with a Xe (150 W) lamp as the excitation source. The Commission
International de I’Eclairage (CIE) chromaticity coordinates were obtained by using PMS-60 Plus
UV-vis-near IR Spectrophotometer (EVERINE, China). The decay curves were measured with an
Edinburgh Instruments FLS980 time-resolved fluorescence spectrophotometer using a microsecond
flashlamp (F920) as excitation source. To identify the micro appearance of Cu NPs, transmission
electron microscopy (TEM, JEOL2100) with an accelerating voltage of 200 kV was utilized. The
powder X-ray diffraction (XRD) patterns were measured on D8 Focus diffractometer (Bruker). X-ray
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photoemission spectroscopy (XPS) was measured by a PHI VersaProbe II, which are utilized to
identify the valences of Sn. All of the above optical measurements were performed under room
temperature.
Fig S1. Dependence of IS0/IS of Cu+ on doped Tb3+ concentration of C3/3 (a), C6/3 (b), C8/3 (c), and C10/3
(d) for G-4CuTbm (m=0-10).
Fig S2. Decay curve tests of G-4CuTbm (m=0-10) monitored at 438 nm for Sn2+ emission under an
excitation of 298 nm.
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Fig S3. (a) PLE and PL spectra of G-1.6Sn. (b) Transmission spectra, (c) PL and (d) PLE spectra of
Tb3+/Cu+/Sn2+-doped glasses.
Fig. S3(b) gives TRA spectra of multi-activators doped glasses, aiming to testify the effect of
Sn2+ doping on states of copper. Typical bands peaked at 560 nm cannot be observed, which suggests
that there are not Cu NPs in Sn2+-doped glasses. Compared with G-1.6SnTb4.5, the absorption edge of
G-4CuTb4.5Sn1.6 experiences a considerable red shift due to the introduction of Cu+ cations.17
Interestingly, a remarkable drop in the absorption intensity of Cu2+ at 800 nm was observed in
G-4CuTb4.5Sn1.6 because of the potential chemical reduction of Cu2+ by SnO, which could be
described as Sn2++2Cu2+→Sn4++2Cu+. Herein, the Sn4+ and Cu2+ make no contribution to the
photoluminescence, and the Cu+ and Sn2+ are the emission centers.
To prove the above deduction, Fig. S3(c) shows the PL spectra of Tb3+/Cu+/Sn2+ doped glasses.
Upon 298 nm excitation, the emission originated from Tb3+ in G-4.5Tb is very weak. In contrast, a
stronger green light was observed in G-1.6SnTb4.5, demonstrating the ET of Sn2+→Tb3+. In addition,
compared with G-1.6SnTb4.5 and G-4CuTb4.5, a continued rise in the PL intensity of Tb3+ is detected
in G-4CuTb4.5Sn1.6, which could be ascribed to the dual potential ETs of Cu+→Tb3+ and Sn2+→Tb3+.
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The above observation can be further certified by the PLE spectra in the inset of Fig. S3(c). The PLE
spectrum monitored at 546 nm in 200-340 nm is similar to the excitation bands monitored at 384 (for
Sn2+) and 438 (for Cu+) nm in G-4CuTb4.5Sn1.6.
The PLE spectra of Tb3+/Cu+/Sn2+ single and co-doped samples were depicted in Fig. S3(d). By
comparing the PLE spectrum of G-4.5Tb, an additional excitation band peaked at 286 nm is found in
the PLE spectrum (λem=546 nm) of G-1.6SnTb4.5, further reflecting the result of ET of Sn2+→Tb3+.
Significantly, compared with the additional excitation band peaked at 298 nm from Cu+ in
G-4CuTb4.5, the PLE intensity of the additional band rises dramatically in G-4CuTb4.5Sn1.6, which
could be associated with the enhanced ET of Cu+→Tb3+, i.e., the efficient reduction of Cu2+ to Cu+ by
SnO could lead to increased content of Cu+ and the subsequent enhancement of ET from Cu+ to Tb3+.
Fig S4. PLE (λem=377 nm) and PL (λem=288 nm) spectra of G-tSn (t=0.8-2.4) glasses.
Fig. S4 shows the dependence of PLE and PL spectra of G-tSn (t=0.8-2.4) on Sn2+ concentration.
Monitored at 377 nm, G-tSn presents asymmetric excitation bands in 200-350 nm. The excitation
band of G-2.4Sn can be deconvoluted into two symmetric sub-bands peaked at 246.8 and 291.5 nm.
Moreover, the excitation band shifts from 282 to 288, and then to 292 nm with the increment of SnO.
Excited by 288 nm, G-2.4Sn exhibits an emission band peaked at 388 nm, relating to the T1-S0
relaxation in the Sn2+-activated glasses. The emission band can be deconvoluted into two Gaussian
files peaked at 372.6 and 420.3 with an energy difference of 3045.9 cm-1. With rising SnO content, the
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excitation and emission intensities of G-tSn monotonously rise due to the concentration effect of Sn2+.
Significantly, the emission band of Sn2+ experiences a red shift from to 372 to 377, and then to 388
nm, which may be ascribed to the decline in the T1 excited levels of the Sn2+ emission centers. The
red-shift phenomena can be further affirmed by the red shift of the absorption edge of G-tSn in Fig.
S5(a).
Fig S5. (a) UV-VIS absorption spectra of G-Host, and G-tSn (t=0.8-2.4). (b) ABS spectra of G-Host,
G-4Cu, G-CuSi0.8, G-4CuSn2.4, G-4CuTb4.5, G-4CuTb4.5Si1.8, and G-4CuTb4.5Snz (z=0.8-2.4).
The inset depicts the enlarged absorption range between 200 and 400 nm.
Fig. S5(b) gives the ABS spectra of Sn2+/Cu+/Tb3+/Si single and co-doped glasses. Compared
with G-4Cu, a remarkable drop of the Cu2+ absorption band peaked at 800 nm is found in G-4CuSi0.8
and G-4CuSn2.4, due to the reduction of Cu2+ to Cu+ by SnO and Si powder. And the absorption
intensity of Cu2+ in G-4CuSi0.8 is stronger than that of in G-4CuSn2.4, which indicates that
G-4CuSn2.4 may contain more Cu+ cations. Besides, the intensity of Cu2+ band declines greatly in
G-4CuTb4.5Sn0.8 comparing with G-4CuTb4.5. With increasing SnO content, further decrease in the
absorption band of Cu2+ is not detected in G-4CuTb4.5Snz (z=1.6-2.4), which suggests that the
content of Cu+ could be fixed in SnO-rich glasses.
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Fig S6. PLE spectra of G-4Cu, G-4CuSi0.8, G-4CuSn2.4, and G-2.4Sn glass samples. The olive
dash-dotted line shows the difference spectrum (λem=438 nm) of G-4Cu and G-4CuSi0.8, and the red
dash dot-dotted line is the difference spectrum (λem=438 nm) of G-4CuSn2.4 and G-4Cu.
As shown in Fig. S6, it is noticed that the difference spectrum with a peak only can be found in
DiffCuSi, indicating that the main role of Si powder is to produce Cu+ from Cu2+.
Fig S7. (a) PL spectra, (b) dependence of emission intensity as a function of doped Tb3+ concentration
with fixed SnO content, (c) calculated ET efficiencies for Sn2+→Tb3+, (d)PLE spectra, and (e) decay
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curves of G-2.4SnTbn (n=0-9.0).
Fig S8. Dependence of calculated IS0/IS of Sn2+ on C3/3 (a), C6/3 (b), C8/3 (c), and C10/3 (d).
Energy Transfer from Sn2+ to Tb3+ in Amorphous Borate Glasses.
To further confirm the ET of Sn2+→Tb3+, Fig. S7(a) reveals the PL spectra of G-2.4SnTbn
(n=0-9.0) without Cu+ doping. The variation includes the emission bands of both Sn2+ and Tb3+ cations.
With ascending Tb3+ content, one finds the PL intensity of Sn2+ (at 388 nm) gradually descends, while
PL intensity (at 546 nm) of Tb3+ first greatly rises to a maximum at n=4.5 and then decreases as a
result of concentration quenching effect, evidencing the ET from Sn2+ to Tb3+. The above results can
be directly observed in Fig. 7S(b). Based on Eq (1), the calculated ET efficiencies are plotted as a
function of Tb3+ content and represented in Fig. S7(c). With rising Tb3+, ET ascends and reaches
92.1% at n=9. The dependence of the enhancement times of Tb3+ emission on Tb3+ concentration is
shown in inset of Fig. S7(a). Surprisingly, an enhanced emission of Tb3+ by 66 times was observed in
G-2.4SnTb4.5 excited by the optimal UV-light of 292 nm.
Fig. S7(d) shows the PLE spectra of G-2.4SnTbn by monitoring at 546 nm. The additional bands
in 200-340 nm are almost similar to PLE spectrum of G-2.4Sn monitored at 388 nm. Fig. S7(e) gives
the decay curves of G-2.4SnTbn. The fluorescence of Sn2+ decays faster with rising Tb3+ content. The
decay processes of G-2.4SnTbn are characterized by average decay lifetime, which can be derived by
Eq (4). The average lifetime were determined to be 6.828, 5.832, 5.110, 3.670, and 1.218 s for
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G-2.4SnTbn with y=0, 1.5, 3, 6, 9, respectively. These results prove the highly efficient ET of
Sn2+→Tb3+ occurs.6
Based on Dexter’s ET formula of multipolar interaction and Reisfeld’s approximation6, 9, 30, ET
between Tb3+ and Sn2+ could be processed through electric-multipole interactions and exchange
interaction, which both belong to the resonant energy-transfer. Thus, according to the above Eq (2)
and Eq (3), plots of IS0/IS of Sn2+ and Cα/3 (α=3, 6, 8, 10) for G-2.4SnTbn (n=0-9.0) are shown in Fig.
S8. The best linear behavior with the high goodness of fit (R=99.80%) was observed only when α=8.
This result indicates that the nature of multipolar interaction for ET of Sn2+→Tb3+ is principally
governed by a dipole-quadruple interaction. A similar observation was also discussed in Fig. S1.
Fig S9. XRD patterns of G-4CuTb4.5Sip (p=0-5.2) glasses.
Fig S10. (a) Typical TEM micrograph of G-4CuTb4.5Si5.2 glass sample. (b) The HRTEM image for a
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single copper nanoparticle in the synthesized glass.
Fig S11. (a) Decay curves (λex=368 nm, λem=546 nm) and (b) variation of calculated average decay
lifetimes of Tb3+ in G-4CuTb4.5Sip (p=0-5.2) samples.
To further understand the EET between Cu NPs and Tb3+, decay curves of G-4CuTb4.5Sip
(p=0-5.2) excited at 368 nm and monitored at 546 nm were given in Fig. S11(a). The decay processes
can be well fitted by a single exponential decay mold using the equation:25
I (t)  I 0 exp( t/  )
(8)
in which the I0 and I(t) represent the PL intensities at time 0 and t, and  is decay time. The average
decay times are derived to be 1.990, 2.208, 2.594, 2.752, and 2.844 ms for G-4CuTb4.5Sip (p=0-5.2),
which can be directly observed in Fig. S11(b). In general, the rise of Tb3+ content can lead to a
decrease in the decay lifetime of Tb3+, and both the ion-ion interaction and the cross-relaxation in the
excited states of Tb3+ are increased. In our case, the lifetime rise in G-4CuTb4.5Sip suggests that the
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formation of Cu NPs could result in the decline of the Tb3+-Tb3+ interaction. And the effect of SPR
absorption of Cu NPs on emission behavior of Tb3+ is similar to the influence of the decrease in Tb3+
doped concentration by deactivating luminous Tb3+ cations through transferring energy transfer to
nanoscale metal. Herein, the interband transitions from the excited states of Tb3+ to nanoscale Cu0
particles could be devoted to the PL quenching of Tb3+, instead of the plausible cross-relaxation
induced excitation energy transfer between Tb3+-Tb3+.
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