Supporting Information
The CaF2 with 1 mol% Yb3+ concentration showed the most intense CL, as shown
in Figure S1. At low Yb3+ concentrations (<0.05 mol%), the dopant ions mainly form
isolated centers, so the CL intensity was extremely low. The CL intensity increased
gradually as the increasing of dopant concentration and reached the maximum with 1
mol% Yb3+. The CL intensity was decreased as further increasing the concentration,
which is likely due to energy migrations from Yb3+ ions to quenching centers.
Figure S1. NIR emission intensities, CL intensities of Yb3+ dimers and Yb3+ trimers
change with dopant concentrations of Yb3+ ions.
Figure S2 shows that no emission peaks were observed in other regions (outside
the range of CL for Yb trimers and dimers). The emission band ranging from 480 nm
to 560 nm attributes to the CL of Yb3+ dimers. For the emission band peaking at 345 nm,
we characterized the emission by intensity dependence (Figure 1c), fluorescence decay
times (Figure 1d), and fine spectra having corresponding relationships (Figure 2b and
Figure 2d). These unique properties of CL are completely different from that of
upconversion processes of other Ln3+ (especially Er3+ and Tm3+) ions.
3+
CaF2:Yb ex = 980 nm
Intensity (A.U.)
PMT voltage / slit width
700 V / 2.5
400 V / 2.5
400 V / 1.0
At room temperature
300
400
500
600
Wavelength (nm)
700
800
Figure S2. CL spectra of CaF2:Yb3+ under different test parameters (PMT:
Photomultiplier Tube). The spectra were measured by using a Hitachi F4500
fluorophotometer.
In order to further investigate the possible contributions of impurities, we
intentionally added Ln3+ ions (Er3+, Ho3+, Eu3+, Tb3+ and Tm3+) to CaF2:Yb3+ and the
emission spectra of them were showed in Figure S3. Obviously, all the impurities
showed emission bands in other regions or out of the CL regions.
Only Yb3+/Tm3+ co-doped CaF2 showed emission bands within the CL region, 320
nm to 360 nm. However, Figure S3a indicates that the emission reported in our
manuscript couldn’t be derived from Tm3+ impurity. Other impurities didn’t show
emission peaks within the region of Yb3+ trimers, so we can easily ruled out them.
Figure S3b also indicates that these impurities mainly quench the CL of Yb3+ trimers,
as we hardly observed the emission band of Yb3+ trimers if we had observed the
emission bands of impurities. Therefore, we can fully confirm that our new
observations come from CL of Yb clusters and no emissions from impurities of Ln3+
were observed in our samples.
Figure S3. (a) Full scan emission spectra of Yb3+ doped and Yb3+/Ln3+ (Er3+, Ho3+,
Eu3+, Tb3+ and Tm3+) co-doped CaF2. (b) UV region emission spectra of these doped
and co-doped materials, as well as the convolution spectrum and low temperature
spectra of Yb3+ trimers.
We used a PMT detector equipped with a 1800 lines/mm grating to measure the
UV and green regions. The detector was calibrated by using a SL1-CAL Tungsten
Halogen (StellarNet, Inc). Figure S4 showed standard spectrum of the Tungsten
Responsivity
Halogen lamp, measured spectrum, and the response curve of the detector.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
300
PMT detector (A)
SL1CAL tungsten halogen (B)
Response curve (A/B)
(500, 2.30)
(340, 2.38)
350
400 450 500
Wavelength (nm)
550
600
Figure S4. Calibration curve of the spectra measurement system.
Figure S5a shows the emission spectrum of Yb3+ trimers measured at room
temperature. Figure S5b shows the emission spectrum of Yb3+-dimers obtained under
the same excitation and collection conditions as those in Figure S5a, and a combination
of three neutral density filters (The transmittances are 15%, 20%, and 25%,
respectively.) with the total transmittance of 0.75% were placed in front of the
collection entry of monochromator so that the emission intensities were in the linear
range of the instrument. Based on the transmittance of the filters, the emission intensity
was back-calculated after integrating emission spectrum over the wavelength range.
The results were showed in Table S1. The two spectra were calibrated by using
response curve showed in Figure S4 (blue line).
Figure S5. Emission spectra of Yb3+ trimers (a), Yb3+ dimers (b) and schematic
instrument setup for measuring the UC luminescence (c).
Table S1. Calculation results of emission intensities.
The emission intensity of Yb3+ trimers
The measured emission intensity of Yb3+ dimers
Transmittance of the filters
The actual emission intensity of Yb3+ dimers
The emission intensity ratio
522
78510
0.75% (15%*20%*25%)
10468000
20054 ≈ 2×104
For the peaks marked as A, AA, and AAA in Figure 2c and 2d, we calculated the
CL energy to designate them. For peak AA, we calculated the CL between 980 nm
and 980 nm, whose result was 490 nm (AA = 1/(1/980+1/980)). For peak AAA, the
result was 326.6 nm (AAA = 1/(1/980+1/980+1/980)). Other peaks were calculated
by using the same method as the examples. Then we designated them according to the
peak positions.