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Laboratory

Optical Characterization of Nanoparticles

The Electrical Engineering/Physics Module will teach you to perform absorption/ transmission and fluorescence measurements on nanomaterials. You will learn to: (i) operate a spectrometer and a light source, (ii) set up absorption/transmission and fluorescence measurements, and (iii) interpret absorption/transmission and fluorescence spectra of CdSe/ZnS core/shell quantum dot dispersions. (ADD PDF LINK)

Pre-lab Exercises
Be prepared to answer these problems before coming to lab. We will discuss the answers during the first laboratory session.

1.   Review lecture notes from ChE 59808 Nanomaterials Course (available on blackboard): Nanoparticles_Size-dependent_effects.pdf.
2.   What is a diffraction grating? How does it work (the grating equation)?
3.   How does a spectrometer employ the grating to get a signal power spectrum?
4.   Why does the spectrometer posses an input “slit”?
5.   Why does it employ curved mirrors?
6.   What imaging function does the spectrometer optics perform?
7.   What affects the resolution of a spectrometer?
8.   What is the difference between fluorescence and phosphorescence?
9.   What does a typical emission spectrum of a general use halogen lamp look like? What does the emission spectrum of the sun look like?
10. What is divergent light?
11. What is a collimator? What does it do?

Lab Exercises

Experiment 1: Absorption Spectra of three Quantum Dot Dispersions
In this experiment you will measure the absorption spectra of three quantum dot dispersions in toluene.

1.   Create a new folder on the laboratory computer with your team’s number and the date of the experiments before you start your experiments.
2.   Set the optical bench up for an absorption measurement. You will need the LS-1 light source, the FVA-UV attenuator, the cuvette holder, three fiber cables, the SD2000 spectrometer, a blank cuvette filled with toluene, and three cuvettes with quantum dot dispersions.
3.   Take a dark spectrum of your set up with the empty cuvette holder and the source switched off. Save the dark spectrum.
4.   Put the toluene blank into the cuvette holder. Take a reference spectrum of the toluene blank. Safe the reference spectrum of toluene.
5.   Exchange the toluene blank for one of the three quantum dot dispersions. Take the absorption spectrum of the quantum dot dispersion. Save the absorption spectrum.
6.   Repeat task 4 for the other two quantum dot dispersion.
7. Repeat steps 4 to 5 at least three times for statistical analysis of the obtained data.

Experiment 2: Fluorescence Spectra of three Quantum Dot Dispersion

In this experiment you will measure the fluorescence spectra of three quantum dot dispersions in toluene.

1.   Set the optical bench up for a fluorescence measurement. You will need the LS-1 light source, the FVA-UV attenuator, the cuvette holder, three fiber cables, the SD2000 spectrometer, a blank cuvette filled with toluene, and three cuvettes with quantum dot dispersions.
2.   Take a dark spectrum of your set up with the empty cuvette holder and the source switched off. Save the dark spectrum.
3.   Put the toluene blank into the cuvette holder. Take a reference spectrum of the toluene blank. Safe the reference spectrum of toluene.
4.   Exchange the toluene blank for one of the three quantum dot dispersions. Take the fluorescence spectrum of the quantum dot dispersion. Save the fluorescence spectrum.
5.   Repeat task 4 for the other two quantum dot dispersion.
6. Repeat steps 4 to 5 at least three times for statistical analysis of the obtained data.

Experiment 3: Analysis of Quantum Dot Mixtures in Toluene
In this experiment you are given a mixture of an unknown number of quantum dots. Determine: 1) How many different quantum dot sizes are in the solution? 2) What is the emission wavelength for each of the quantum dot sizes? 3) Can you produce isolated fluorescence spectra of each quantum dot size?

1.   Set the optical bench up for an absorption measurement. You will need the LS-1 light source, the FVA-UV attenuator, the cuvette holder, the LVF-HL band pass linear filter, three fiber cables, the SD2000 spectrometer, a blank cuvette filled with toluene, and the cuvette with the quantum dot mixture.
2.   Take a dark spectrum of your set up with the empty cuvette holder and the source switched off. Save the dark spectrum.
3.   Put the toluene blank into the cuvette holder. Take a reference spectrum of the toluene blank. Safe the reference spectrum of toluene.
4.   Exchange the toluene blank for the quantum dot mixture. Take the absorption spectrum of the quantum dot mixture. Save the absorption spectrum.
5.   Rearrange your set up for a fluorescence measurement. Take the fluorescence spectum of the quantum dot mixture. Save the fluorescence spectrum.
6.   Modify your set up such that you can take individual fluorescence spectra of the quantum dots using the LVF-HL band pass linear filter. Record and save the individual fluorescence spectra of the quantum dots contained in the mixture.
7.   Perform the Post-Lab exercises and turn them in with your lab report for the Electrical Engineering/Physics Module 2.

Post-Lab Exercises

Use your absorbance and fluorescence data and any necessary Excel spreadsheet or curve fitting software to perform these exercises.
1.   Plot your absorbance data as a function of wavelength for all three quantum dot dispersions. Indicate which part of the spectra is due to the absorption of the quantum dots.
2.   Determine the absorption wavelength for each quantum dot size. Indicate the accuracy of your measurement by calculating the standard deviation from the averaging of your multiple measurements.
3.   Plot your fluorescence data as a function of wavelength for all three quantum dot dispersions.
4.   Determine the emission wavelength of the three quantum dot dispersions. Indicate the accuracy of your measurement by calculating the standard deviation from the averaging of your multiple measurements.
5.   Compare your absorption and emission data with the absorption and emission values given on the product sheet provided by Evident Technology. If there is a deviation, speculate what causes the deviation.
6.   Answer the questions for Experiment #3: 1) How many different quantum dot sizes are in the mixture? 2) What is the emission wavelength for each of the quantum dot sizes in the mixture? 3) Were you able to produce isolated fluorescence spectra for each quantum dot size using the LVF-HL band pass linear filter?
7. Are the emission wavelengths obtained from the mixture identical to those obtained from the mixture using the LVF-HL band pass linear filter? If they are not, speculate on the origin of this deviation.