Quantum Yield Measurement of the Up-Conversion Phosphors

Download PDF September 12, 2017

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.

Figure 2. FP-8700 Up-conversion system.

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 Bandwidth5 nmData Acquisition Interval0.2 nm
Response Time0.2 secScan Speed1000 nm/min
Laser Wavelength980 nmLaser Output150 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.

MeasurementArea of Excitation LightArea of Scattered LightArea of AbsorptionArea of FluorescenceSample Absorbance (%)Internal Quantum Yield (%)
12.8 x 1062.14 x 1066632701453.8623.690.22
22.73 x 1062.14 x 1065878401378.8421.570.23
32.83 x 1062.14 x 1066876201433.824.280.21
Figure 4. Excitation and scattered light (left) spectra and the fluorescence spectrum (right) of YTa7O19: Ho4, Yb60.

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

MeasurementArea of Excitation LightArea of Scattered LightArea of AbsorptionArea of FluorescenceSample Absorbance (%)Internal Quantum Yield (%)
12.75 x 1062.07 x 106685000501.57224.880.073
22.80 x 1062.09 x 106708860498.8125.320.070
32.87 x 1062.05 x 106821920515.89928.590.063
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.

MeasurementArea of Excitation LightArea of Scattered LightArea of AbsorptionArea of FluorescenceSample Absorbance (%)Internal Quantum Yield (%)
12.75 x 1061.92 x 10683334031500.130.323.78
22.75 x 1061.91 x 10684517032176.730.733.81
32.77 x 1061.95 x 10681933031277.229.553.82
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.

MeasurementArea of Excitation LightArea of Scattered LightArea of AbsorptionArea of FluorescenceSample Absorbance (%)Internal Quantum Yield (%)
12.74 x 1062.14 x 106594410501.34121.710.084
22.86 x 1062.16 x 106698340446.07124.440.064
32.76 x 1062.14 x 106620210566.94122.450.091
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.

MeasurementArea of Excitation LightArea of Scattered LightArea of AbsorptionArea of FluorescenceSample Absorbance (%)Internal Quantum Yield (%)
12.74 x 1062.08 x 106663190908.77724.220.14
22.83 x 1062.16 x 106664660863.49623.510.13
32.85 x 1062.20 x 106654600843.46822.970.13
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, Yb80 complex (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

About the Author

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