Introduction

The up-conversion is the process of multi-step excitation to produce the fluorescence light whose wavelength is shorter than the one of excitation light (Refer to Fig.1). This is expected to be used for following applications; (1) labeling for bio-imaging, (2) anti-counterfeit ink, (3) development of solar cell for infrared light.

The up-conversion fluorescence intensity is proportional to the n-th power of the excitation intensity, where n is the number of photons for excitation. Therefore, the researchers who develop the up-conversion phosphors are interested in the up-conversion fluorescence intensity measurement for analyzing the excitation process of the material, and are also interested in the up-conversion quantum yield measurement. Generally, the quantum yield of up-conversion material is very low, and the measurement system with high-sensitivity is required.

JASCO have developed the up-conversion quantum yield measurement system, which can detect the very small fluorescence by using laser.

As a example of measurement, this report shows the quantum yield measurement of the up-conversion phosphors with heavy rare earth.

Experimental

Sample
1. YTa₇O₁₉: Er₁₀, Yb₄₀
2. YTa₇O₁₉: Ho₄, Yb₆₀
3. YTa₇O₁₉: Tm₃, Yb₈₀
4. RETa₇O₁₉: Er₉₀, Tm₁₀
5. GdTa₇O₁₉: Er₁₀, Yb₄₀
6. Gd₂O₃: Er₅, Yb₁₀

Measurement parameters
Emission bandwidth: 5 nm
Scan speed: 1000 nm/min
Response: 0.2 sec
Data acquisition interval: 0.2 nm
Laser wavelength: 980 nm
Laser output: 150 mW

Keywords

Up-conversion phosphors, quantum yield, heavy rare earth

Results

In order to evaluate the measurement reproducibility, each sample was measured for three times.

Fig.3 – 8 show the following spectra of each sample; (1) spectrum of excitation light, (2) spectrum of scattered light, (3) fluorescence spectrum. Table 1- 6 show the analysis result of quantum yield measurement.

As show in the tables except for table 3 (YTa₇O₁₉: Tm₃, Yb₈₀), this system could evaluate the quantum yield less than 1%.

1. YTa₇O₁₉: Er₁₀, Yb₄₀

Fig.3 The scattered light spectra and the fluorescence spectra
(Blue: first, Green: second, Red: third)

Table.1 Result of internal quantum yield

2. YTa₇O₁₉: Ho₄, Yb₆₀

Fig.4 The scattered light spectra and the fluorescence spectra
(Blue: first, Green: second, Red: third)

Table.2 Result of internal quantum yield

3. YTa₇O₁₉: Tm₃, Yb₈₀

Fig.5 The scattered light spectra and the fluorescence spectra
(Blue: first, Green: second, Red: third)

Table.3 Result of internal quantum yield

4. RETa₇O₁₉: Er₉₀, Tm₁₀

Fig.6 The scattered light spectra and the fluorescence spectra
(Blue: first, Green: second, Red: third)

Table.4 Result of internal quantum yield

5. GdTa₇O₁₉: Er₁₀, Yb₄₀

Fig.7 The scattered light spectra and the fluorescence spectra
(Blue: first, Green: second, Red: third)

Table.5 Result of internal quantum yield

6. Gd₂O₃: Er₅, Yb₁₀

Fig.8 The scattered light spectra and the fluorescence spectra
(Blue: first, Green: second, Red: third)

Table.6 Result of internal quantum yield

References

Data courtesy of Dr. Kouji Tomita, Department of Chemistry, School of Science, Tokai University