Question

Procedure 1. A 25 mL round bottom flask equipped with a stir bar is loaded with 13 mg of CdO powder, 0.6 mL of oleic acid, and 10 mL of 1-octadecene. The reaction flask is placed into a heating mantle and surrounded with aluminum foil so that the temperature can reach 225 °C, which will take approximately 1 hr. Some hot plates may heat up faster and the experiment can be performed sooner. 2. As the CdO solution is heating, the Se solution should be prepared. Five students can share the Se solution, since only 1 mL is required for each reaction. A 25 mL round-bottom flask equipped with a stir bar is loaded with 30 mg of Se and 5 mL of 1-octadecene and allowed to stir at room temperature. To this stirred solution was added 0.4 mL of trioctylphosphine via syringe. The mixture will turn homogeneous. At this point it is ready for the next step. 3. Once the CdO solution has reached a temperature of about 225 °C, add 1 mL of the Se solution from step 2 in a rapid fashion. As soon as you add the Se solution start collecting samples of approximately 1 mL into separate test tubes continuously as the reaction will be changing colors from yellow to orange to blood red. 4. After allowing the quantum dot solutions to cool, add 1 mL of pentane to the test tube containing ~1 mL of sample. Then, pipette the samples into a glass cuvette to record their UV-Vis spectra. Use pentane as the blank. The solutions collected in test tubes can be stored overnight in the hood or drawer without decomposition if there is not enough time to record UV-vis spectra.

What wavelength light does bulk CdSe absorb?

Answer 1

(CdSe) QDs in octadecene (OTD) solution is innovation-driven cost reductions of photovoltaic material. The synthesis by heating OTD to followed by the addition cadmium oxide (CdO), trioctlyphosphine (TOPO), oleic acid (OA) and selenium (Se) solution

This synthesis gives colloidal CdSe QDs, which can be characterised using absorption spectroscopy (UV-Vis).

the quantum dot solution in pentane is used to record their UV-Vis spectra. Use pentane as the blank.

What wavelength light does bulk CdSe absorb?

For characterization of optical properties CdSe Quantum Dot , we need to compare its UV-Vis absorbance with that of bulk CdSe :

Bulk CdSe crystal corresponding to E_g≈ 1.8 eV at room temperature.

Thus wavelength light does bulk CdSe absorb :

   Eg = 1.8*1.6*10^-19 J

E = hc/ λ

λ = hc/E = (6.626*10^-34 J-s * 3*10⁸ m/s )/ 2.88*10^-19 J

λ = 6.9*10⁷ m = 690 nm