Supporting Information
High multi-photon visible upconversion emissions of Er3+
singly-doped BiOCl microcrystals: a photon avalanche of Er3+
induced by 980 nm excitation
Yongjin Li, Zhiguo Song, Chen Li, Ronghua Wan, Jianbei Qiu, Zhengwen Yang,
Zhaoyi Yin, Yong Yang, Dacheng Zhou, Qi Wang
School of Materials Science and Engineering, Kunming University of Science and
Technology, Kunming, 650093, China

Corresponding Author: E-mail: songzg@kmust.edu.cn
Characterization
The downshifting luminescence lifetimes were measured on an Edinburg
Instruments FLS920 spectrofluorimeter equipped with both continuous (450 W) and
pulsed xenon lamps. The NIR luminescence spectra were obtained using a ZOLIX
SBP300 spectrophotometer under excitation of 980 nm LD. All the measurements
were performed at room temperature.
Fig. S1. UC emission lifetime decay curves of Er3+ doped BiOCl microcrystals under
excitation at 980 nm with power density of 90 W/cm2 (upon threshold) and 55 W/cm2
(below threshold). (a) 4S3/2 level and (b) 4F9/2 level upon threshold; (c) 4S3/2 level and
(d) 4F9/2 level below threshold.
Fig. S1 shows the upconversion (UC) emission lifetimes of the green (4S3/2) and
red (4F9/2) excited states in Er3+ doped BiOCl microcrystals following excitation with
980 nm. The upconverted decay curves for all samples under investigation deviated
slightly from single exponentially. As illustrated in the figure, the excitation power
has no significant effect on the UC lifetimes of 4S3/2 and 4F9/2 level, but all the UC
lifetimes of the samples upon power threshold point are all slightly longer that those
below power threshold point. Furthermore, as the concentration of Er3+ ions increase, both
the lifetimes of 4S3/2 and 4F9/2 level increase at first and then decrease when Er3+ ion dopants is
over 4.0 mol%, which is same to the dependence of UC emission intensity on the Er3+ dopant
concentration. The dependence of UC lifetimes on the excitation power and the Er3+ dopant
concentration could be considered due to increasing percentage contributions from energy
transfer upconversion (ETU) processes to the UC emissions of Er3+, which can prolong the
UC luminescence lifetime. Because of the UC processes, increasing excitation power
can promote the ETU as done by increasing Er3+ dopant concentration. It can be
confirmed partly by the different performances of lifetime through downshift processes,
excited by UV light (Fig. S2). The detailed theoretical analysis for the influence of ETU
on the UC lifetimes of Er3+ ions can refer to Ref.1. Above results indicate that lifetime
probably is not the key factor for initiating PA behavior, but there exist strong and
efficient CR processes determined by Er3+ ion concentration.
Fig. S2 exhibits the luminescence decay curves of (a) 4S3/2 and (b) 4F9/2 level of
Er3+ doped BiOCl microcrystals under 380 nm excitation were fitted using a single
exponential function. It show that the lifetimes of 4S3/2 and 4F9/2 level, through
downshifting processes, also have normal values similar to other reports, but decrease
with increasing Er3+ dopant concentration, which exhibit a typical concentration
quenching effect [2].
Fig. S2. Luminescence decay curves of (a) 4S3/2 and (b) 4F9/2 level of Er3+ doped
BiOCl microcrystals under 380 nm excitation.
Fig. S3. NIR fluorescent spectra of BiOCl: Er3+ (0.25 mol%) microcrystals under the
excitation of 980 nm. The inset is the power dependence of the NIR emission.
Fig. S3 shows the NIR fluorescent spectra of the BiOCl: 0.25 mol% Er3+ under
the excitation of 980 nm. The NIR emission band at 1550 nm, correspond to the 4I13/2
→ 4I15/2 transitions of Er3+ ions, can be observed. The inset displays in a double
logarithmic scale the pump power dependence of the 1550 nm fluorescence. The
result shows that the NIR emission also presented a looping behavior over the
threshold point of excitation power, similar to other reports [3, 4], which partly
supports the PA mechanism we proposed. In order to confirm the accuracy of
experimental
data,
the
NIR
emission
of
Er3+-doped
silicate
glass
(55SiO2-25CaO-5Na2O-15 K2O-0.25Er2O3, mole %) was presented as a comparison,
which exhibited a typical linear relationship between emission intensity and excitation
power.
References
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96, 661 (2004).
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G. Y. Chen, H. J. Liang, H. C. Liu, G. Somesfalean, and Z. G. Zhang, J. Appl. Phys.
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G. Chen, L. Yang, C. Xu, S. Hao, H. Qiu, L. Sun, Y. Xu, and C. Yang, Opt. Lett. 37,
1268 (2012).