Absolute Quantum Yield Measurement of Powder Samples

The overall goal of this procedure is to measure absolute quantum yield of powder samples using a calibrated Hitachi F 7, 000 fluorescent spectrophotometer. The first step of the procedure is to collect the integrating sphere correction factors to account for the reflectivity of the integrating sphere used for the measurements. The next step is to measure the reference and the sample.

Then direct and indirect excitation measurements are used to calculate the corrected quantum yield. Additionally, chroma coordinates are calculated using the fluorescence emission data for the sample. Ultimately, the calculated quantum yield measurements are in accordance to other published data.

Relative quantum yield measurements depend on the selection of a reliable standard. Unfortunately, to date, there are no quantum yield standards available for powder samples. The calor metric method where absolute energy yields are obtained from temperature changes during irradiation is based on the simple concept of comparing the increase in temperature of an irradiated luminescent sample against the increase in temperature of a non luminescent material of similar optical density.

The absorbed energy is calculated from the ratio of the changes in temperature of the two samples. Then a formula is applied to calculate the quantum yield. The calor metric method does not take into consideration energy reabsorption by the sample and depends on the accuracy of the temperature measurement, which is usually low.

These limitations can be overcome by using a well-designed fluorescence quantum yield measurement system and taking measurements of the spectral distribution, including both the excitation and emission regions. With these refinements in place, this method becomes valuable as a way to confirm quantum yield readings obtained using other techniques. This video features a Hitachi F 7, 000 fluorescence spectrophotometer equipped with the quantum yield measuring Accessory and report generator program.

The F 7, 000 is equipped with a high sensitivity extended range R 9 28 F photo multiplier detector to generate spectral correction factors for the instrument. The F 7, 000 is accessorized with rumine, B diffuser, red filter, and substandard light source. To measure quantum yield, the F 7, 000 requires a 60 millimeter integrating sphere, aluminum oxide white tiles, one spectral on white standard two quartz powder cells, aluminum oxide powder, and quantum yield software.

To calculate chroma coordinates, the emission data is processed by the optional report generator software using a custom template prior to using the F 7, 000 fluorescent spectrophotometer, turn it on and allow the xenon lamp to warm up for one hour before using the sampling compartment. When measuring the integrating sphere correction factors, the software automatically selects the measuring test parameters to acquire the diffuser data. Place the diffuser in the standard sample compartment and close it in the software.

Click on the window quantum yield correction factor measurement, and then on diffuser measurement. Next, enter the file name for the diffuser data and click okay to acquire the correction factor for no sample, which is used as a reference. Remove the standard sample compartment from the instrument and install the integrating sphere.

Now, fill the powder cell with aluminum oxide powder up to a height of at least 25 millimeters. Make certain the powder fully covers the port of the integrating sphere. Tap the bottom of the cell carefully to compact the powder.

Place the aluminum oxide white tile in integrating sphere port facing the emission monochromator. This is the reference port. Then place the powder cell with aluminum oxide in the sample port labeled P one facing the excitation monochromator in the software.

Click on the quantum yield correction factor measurement window, and then on integrating sphere measurement without sample, the software will remind you to set the samples, enter the file name iscore factor F 70, underscore no sample, and click okay. To acquire the correction factor in the presence of a sample, replace the cell with aluminum oxide powder. With the spectral on white standard, the standard must face the excitation monochromator in the software.

Click on the quantum yield correction factor measurement window, and then on integrating sphere measurement with sample, A reminder prompt is provided. Before taking the measurement, enter the file name is factor FCO with sample for the integrating sphere with sample data file and click okay. After each of these measurements, a separate data file is saved in the correct folder of the FL solutions directory.

In this video, the quantum yield of sodium salicylate in powder form is measured. This sample spectral characteristics for excitation and emission do not overlap, making it ideal for a demonstration of the photo luminescence method. Measuring quantum yield of samples with overlapping excitation and emission is possible, but the procedure requires additional correction for the cutoff filters used to eliminate scattering peaks.

Quantum yield measurement involves the acquisition of an emission spectrum for both a blank reference and a sample measurement. In the software, select the analytical measurement parameters by clicking on the method button. Select the general tab under measurement mode, select wavelength scan.

Then enter the appropriate information on the operator and accessories. Now click on the instrument tab and enter the instrument parameters appropriate for the sample. Under measurement, no additional settings are required until after the data have been collected.

The scanning speed may be increased to reduce the sample's exposure to light. This might improve the results for some samples before proceeding. Review the settings and click the okay button in order to set the selected measuring parameters in the instrument.

At this point, it is possible to save the selected settings for future use before proceeding. Remember to compact the sample by tapping the bottom of the cell. This will produce a more uniform surface leading to better measurements.

For best results, always use fresh samples that are stored according to the manufacturer's conditions and are protected from light. Also, be aware that similar materials from different manufacturers can yield different results. Now, begin taking measurements with direct excitation by loading the aluminum oxide reference in measuring Port P one.

This is the port facing the excitation side in the software. Click on the sample button, type the sample name, and then click on the box next to AutoFile. Select the folder and file name for the data, and then click save and okay.

Click on the measure button to start measuring the aluminum oxide sample. After the data processing window opens, click on the autoscale access button to adjust the scale. To visualize the scattering peak with direct excitation, now proceed with measuring the sample of sodium salicylate using direct excitation.

Click on the sample icon. Enter the sample and file name, and then click the okay button. Now place the sodium salicylate sample in the powder cell and in the P one port of the integrating sphere, which faces the excitation light beam.

Then click on the measure button. When the data processing window opens, click on the autoscale axis button to adjust the scale and visualize the scattering and fluorescence peaks. To get indirect excitation data, repeat the process of taking measurements of each sample in the P two port of the integrating sphere.

Before taking each measurement, click on the sample button and type the appropriate sample and file name. Place the cell with the aluminum oxide sample in the P two port, the one facing the emission monochromator. Then place the white tile in Port P one, the one facing the excitation monochromator.

Once again, click on the measure button to read the sample. To complete the sample measurement, measure the sodium salicylate sample using indirect irradiation. First, we type the sample in file names as in previous steps.

Remove the aluminum oxide sample from the P two port and replace it with the sodium salicylate sample. Then click the measure button to calculate the quantum yield. Begin by loading the integrating sphere correction factors.

Click on the quantum yield calculation button to open the quantum yield calculation program. Then click on the quantum yield correction factor setting button. From there, click on the integrating sphere correction tab and click the box in front of integrating sphere correction.

Now click the filter correction tab and make sure the filter correction box is unselected. Since we did not use filters for our measurements, click again on the integrating sphere correction tab. Click on the load button of the diffuse measurement data section.

Then select the file iscore factor underscore F 70 underscore diffuser, and click on the load button. Next, click on the load button of the integrating sphere Measurement data without sample section, select and load the file iscore factor underscore F 70, no sample. Now click on the load button of the integrating sphere measurement data with sample section.

Click on the file is factor FCO with sample and click the load button. Normalized wavelength can be left at 600 nanometers or adjusted to the wavelength value where the integrating sphere correction is equal to one. To do this, make sure the box in front of the display quantum yield calculation window is selected, and click the okay button of the quantum yield factor setting window to close the window.

Now click on the integrating sphere correction tab of the quantum yield calculation window and adjust the cursor until the integrating sphere correction reading is one. Make a note of the wavelength, then select the quantum yield correction factor setting and change the normalized wavelength to the reading that was just obtained. Okay, the new setting.

Note that the program limits the value between 600 and 650 nanometers. The next step is to load the baseline and sample data files. Click on the quantum yield calculation tab of the quantum yield calculation window load data without sample for direct excitation by clicking on the load button.

Then load data with sample for direct excitation. Now proceed with selecting the scattering and fluorescence regions using the cursor to calculate the quantum yield for direct excitation of the sample, click on the calculation button and read the results. This data represents the sample taking into consideration direct excitation.

This data is used for the final calculation of the quantum yield. Save it as a text file under the file name QI direct irradiation. Now load data files for aluminum oxide measured using indirect excitation and for sodium salicylate measured using indirect excitation.

Following the same procedure used for direct excitation, expand and select the scattering and fluorescence regions on the left and right windows of the quantum yield calculation window. Then click on the calculation button to calculate the quantum yield data using indirect excitation. Next, save this data for the final quantum yield calculation as a text file with the file name QI indirect irradiation.

Using a spreadsheet, determine the quantum yield for the sample by importing the data in the text files and making the appropriate calculations to calculate chroma of the sample open data file P one sodium salicylate. This is the direct excitation emission data for the sodium salicylate sample. Now click the property button, then the report tab.

Under the output setting select use print generator sheet from the dropdown menu. In print items, select the template file. Then click the open button.

There's no need to select the wavelength range or interval because it is done automatically. The next step is creating the chroma report. To do this, click on the report tab.

This executes the macro and saves the data in the reports folder in the spreadsheet format. Under the sample name. The report opens and executes the macro calculating chromaticity and then closes automatically.

At this time, we can open the C chromaticity report saved under the same name of the sample file used to perform the calculation. The report is basically used to calculate the perceived color of a fluorescent sample. In this case, sodium salicylate rounded numerical results for tristimulus X, Y, Z chroma coordinates XY and dominant wavelength WL are presented on top on rose two and three.

At the bottom of the file are also the numerical results and the CIE chroma diagram showing the position of the perceived color for the sample. Under analysis to begin with diffuser measurement data was collected. Then data work collected from the integrating sphere without sample and data work collected from the integrating sphere in the presence of a sample using a white spectral on standard, picking up data from the quantum yield calculation screens for direct excitation and indirect excitation.

We use the formula in figure eight to calculate quantum yield, taking into consideration indirect excitation of the sample after calculations, these data returned a quantum yield of 0.47 for the sample which is consistent with the reported values between 0.4 and 0.5. This technique paved the way for researchers exploring better luminescent materials for use in new lighting devices and dyes to measure the quantum efficiencies of powder materials. Don't forget that working with fine powder materials can be extremely hazardous, and precautions such as using appropriate protective equipment should always be taken while performing this procedure.