Understand Steps for Measuring Absolute Quantum Yield at A Glance!
Step 1. Set up the excitation light source.
Step 1. Setting up the excitation light source (this article takes a 405 nm laser as an example): The excitation light source is connected to the optical fiber by optical fiber coupling and connected to the integrating sphere.
Figure 1: The picture on the left shows a 405 nm laser light source with a fiber coupling kit, and the excitation light can be output through the fiber.
The picture on the right is the integrating sphere used for the measurement (Photoluminescence Quantum Yield, PLQY). The optical module installed on the side can be connected to the optical fiber, and the excitation light can be introduced into the integrating sphere.
Step 2. Prepare the sample and the blank control device.
Step 2. Prepare the sample: Prepare the test sample and the blank control device for measuring the Photoluminescence Quantum Yield (PLQY). For example, the blank control device of the sample with coating is the glass without coating.
Figure 2: The Sample on the right is a thin film sample to be measured for Photoluminescence Quantum Yield (PLQY), and the Blank on the left is a glass substrate without a coating film compared to the sample on the right.
Step 3. Put the sample and control device into the integrating sphere.
Step 3. Put the blank control and the sample to be measured for Photoluminescence Quantum Yield (PLQY) into the integrating sphere separately. The sample need to be placed vertically to prevent falling out, and the orientation of the sample holder also needs to be noticed. Do keep the direction of the reflection mirror toward the excitation light source.
Figure 3: The PL sample holder is placed from top of the integrating sphere.
The sample is fixed in the groove of the sample holder, and the reflection mirror towards the left to match the incident direction of the excitation light source.
Step 4. Set intensity of the excitation light and measurement time of the spectrometer in Photoluminescence Quantum Yield (PLQY) Test System.
Step 4. Adjust the measurement conditions: First of all, the excitation light intensity can be adjusted according to the test requirements. You can use the mouse to move the output adjustment lever, or directly input the required power. 100% means full output. Second, adjust the measurement time of the spectrometer. It needs to be adjusted according to the conditions of the excitation light intensity in the previous step. Increasing the integration time can make the spectral signal have a high signal-to-noise ratio (more than 100:1 is better), and it cannot be set too long to avoid signal saturation.
Figure 4: The interface on the measurement software used to adjust the excitation light power output, read the signal, and perform preliminary tests.
The “Power” controls the output power of the excitation light, which can be manually input or adjusted with a lever. The integral measurement time of the spectrometer can be adjusted through “Int_Time”, and finally click the Pre Test button to trigger spectrum measurement to check if the settings are suitable or not.
Step 5. Measure the fluorescence spectra of the blank and the sample.
Step 5. Spectral measurement: measure the fluorescence spectra of the blank and the sample respectively. As shown in Figure 7, the blue color is the blank spectrum, and the green color is the sample spectrum. Due to photoluminescence (PL), it can be seen that in the wavelength range of excitation light, the spectrum of the sample is lower than that of the blank, indicating that part of the excitation light has been absorbed by the sample. In the wavelength range of fluorescence, it can be seen the fluorescence spectrum of the sample appears, while the original blank does not.
Figure 5: Screen shot of the Photoluminescence Quantum Yield (PLQY) measurement software.
The corresponding functions on the left are (A) Blank measurement, (B) Sample measurement, (C) Calculated photoluminescence Quantum Yield (PLQY). In the spectral display in the center, the blue color is the blank spectrum, and the green color is the sample spectrum to be measured for Photoluminescence Quantum Yield (PLQY). The black dotted line is the selected excitation light calculation range, and the orange dotted line is the selected fluorescence calculation range.
Step 6.Select the wavelength range and just "one click" for the calculation.
Step 6. Select the calculation wavelength range: After selecting the excitation light wavelength range and the fluorescence wavelength range to be calculated, press the “calculate QE” botton to calculate the Photoluminescence Quantum Yield (PLQY).
If you’re interested in the key for achieving high device efficiency and stability, we recommend you to read more about PLQY (Photoluminescence Quantum Yield or Quantum Efficiency) and it’s applications.