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Quantum Yield Measurement of the Up-Conversion Phosphors

By Leah Pandiscia, PhD

Introduction

Quantum yield is very useful in determining the efficiency of multi-step up-conversion excitation process that results in fluorescence at shorter wavelengths than the excitation light (Figure 1). Molecules can be excited at longer wavelengths where light scattering and absorption do not occur. This is particularly useful for evaluating labels used for biological imaging, materials in infrared solar cells and development of inks for anti-counterfeiting.

Figure 1. Energy diagram of conventional fluorescence (left) and up-conversion fluorescence (right).

Up-conversion fluorescence intensity is proportional to the n -th power of the excitation intensity, where n is the number of excitation photons. When using up-conversion to analyze the excitation processes of materials it is therefore of interest to determine the up-conversion quantum yield.

Since the quantum yield of up-conversion materials is very low, a measurement system with high sensitivity is required. JASCO has developed an up-conversion quantum yield measurement system that can detect very small fluorescence intensities with the use of laser excitation.

This application note reports the up-conversion quantum yield measurement of phosphors with heavy rare earth elements.

Experimental

Measurement Conditions

Emission Bandwidth	5 nm	Data Acquisition Interval	0.2 nm
Response Time	0.2 sec	Scan Speed	1000 nm/min
Laser Wavelength	980 nm	Laser Output	150 mW

Solutions of tryptophan (0.0175 mg/L), humic acid (0.5 mg/L) and folic acid (1mg/L) were prepared in the following mixture ratios (tryptophan: humic acid: folic acid): 6:2:2, 5:5:0, 5:0:5, 4:4:2, 4:2:4, 2:6:2, 2:4:4, 2:2:6, 0:5:5.

Keywords

FP-8700, Fluorescence, up-conversion, quantum yield, near-infrared, NIR phosphors, quantum efficiency, biological dyes, FP0014

Results

The excitation and fluorescence spectra of 6 samples were measured (YTa₇O₁₉: Er₁₀, Yb₄₀, YTa₇O₁₉: Ho₄, Yb₆₀, YTa₇O₁₉: Tm₃, Yb₈₀, RETa₇O₁₉: Er₉₀, Tm₁₀, GdTa₇O₁₉: Er₁₀, Yb₄₀, and Gd₂O₃: Er₅, Yb₁₀). Each sample was measured three times to evaluate the measurement reproducibility. The three measurements are overlaid and shown in different colors in Figures 3-8.

Figure 3. Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of YTa₇O₁₉: Er₁₀, Yb₄₀.

Tables 1- 6 show the quantum yield measurement results.

Table 1. Internal quantum yield measurement results of YTa₇O₁₉: Er₁₀, Yb₄₀.

Measurement	Area of Excitation Light	Area of Scattered Light	Area of Absorption	Area of Fluorescence	Sample Absorbance (%)	Internal Quantum Yield (%)
1	2.8 x 10⁶	2.14 x 10⁶	663270	1453.86	23.69	0.22
2	2.73 x 10⁶	2.14 x 10⁶	587840	1378.84	21.57	0.23
3	2.83 x 10⁶	2.14 x 10⁶	687620	1433.8	24.28	0.21

Table 2. Internal quantum yield measurement results of YTa₇O₁₉: Ho₄, Yb₆₀.

Measurement	Area of Excitation Light	Area of Scattered Light	Area of Absorption	Area of Fluorescence	Sample Absorbance (%)	Internal Quantum Yield (%)
1	2.75 x 10⁶	2.07 x 10⁶	685000	501.572	24.88	0.073
2	2.80 x 10⁶	2.09 x 10⁶	708860	498.81	25.32	0.070
3	2.87 x 10⁶	2.05 x 10⁶	821920	515.899	28.59	0.063

Figure 5. Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of YTa7O19: Tm3, Yb80.

Table 3. Internal quantum yield measurement results of YTa₇O₁₉: Tm₃, Yb₈₀.

Measurement	Area of Excitation Light	Area of Scattered Light	Area of Absorption	Area of Fluorescence	Sample Absorbance (%)	Internal Quantum Yield (%)
1	2.75 x 10⁶	1.92 x 10⁶	833340	31500.1	30.32	3.78
2	2.75 x 10⁶	1.91 x 10⁶	845170	32176.7	30.73	3.81
3	2.77 x 10⁶	1.95 x 10⁶	819330	31277.2	29.55	3.82

Figure 6. Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of RETa₇O₁₉: Er₉₀, Tm₁₀.

Table 4. Internal quantum yield measurement results of RETa₇O₁₉: Er₉₀, Tm₁₀.

Measurement	Area of Excitation Light	Area of Scattered Light	Area of Absorption	Area of Fluorescence	Sample Absorbance (%)	Internal Quantum Yield (%)
1	2.74 x 10⁶	2.14 x 10⁶	594410	501.341	21.71	0.084
2	2.86 x 10⁶	2.16 x 10⁶	698340	446.071	24.44	0.064
3	2.76 x 10⁶	2.14 x 10⁶	620210	566.941	22.45	0.091

Figure 7. Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of GdTa₇O₁₉: Er₁₀, Yb₄₀.

Table 5. Internal quantum yield measurement results of GdTa₇O₁₉: Er₁₀, Yb₄₀.

Measurement	Area of Excitation Light	Area of Scattered Light	Area of Absorption	Area of Fluorescence	Sample Absorbance (%)	Internal Quantum Yield (%)
1	2.74 x 10⁶	2.08 x 10⁶	663190	908.777	24.22	0.14
2	2.83 x 10⁶	2.16 x 10⁶	664660	863.496	23.51	0.13
3	2.85 x 10⁶	2.20 x 10⁶	654600	843.468	22.97	0.13

Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of Gd2O3: Er5, Yb10. — Figure 8. Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of Gd₂O₃: Er₅, Yb₁₀.

Table 6. Internal quantum yield measurement results of Gd₂O₃: Er₅, Yb₁₀.

Conclusion

With the exception of the YTa₇O₁₉: Tm₃, Yb₈₀complex (Figure 6, Table 3), these results demonstrate that the up-conversion system can evaluate quantum yields at levels of less than 1%.

Required Products and Software

FP-8700 Spectrofluorometer
ESC-842 Calibrated WI Light Source

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About the Author

Leah Pandiscia received her PhD from Drexel University where she studied Biophysical Chemistry. She is a Spectroscopy Applications Scientist.

JASCO

Industry

Technique

Quantum Yield Measurement of the Up-Conversion Phosphors

Introduction

Experimental

Keywords

Results

Conclusion

Required Products and Software

About the Author

Industry

Technique

Introduction

Experimental

Keywords

Results

Conclusion

Required Products and Software

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About the Author