Doctor of Philosophy (Ph.D.), Bowling Green State University, 2021, Photochemical Sciences

The growth mechanism of PbSe nanorods is confirmed as one-dimensional oriented attachment and the nano-dipole is the confirmed as the driven force to align the oriented direction along (100). By tuning the length of ligand, the strength of nano-dipolar interaction can be tuned, and this will turn on/off the one-dimensional attachment. Meanwhile, acetic acid is confirmed as the trouble for the branching formation where acetic acid will affect the growth of (111) facet which will change the dipole direction which may changed from (100) to (111) or (110) direction. Beside one-dimensional material, two-dimensional materials (PbS nanosheets) also studied. Oriented attachment growth of PbS nanosheets has been confirmed and chloroalkane is used as co-solvent to initial the oriented attachment. In our further study, chlorine ions can also play a role like chloroalkane and it can form single exponential and long decay lifetime PbS nanosheets. Our post-synthesis treatment of PbS nanosheets by trioctylphosphine can enhance the photoluminescence quantum yield of PbS nanosheets from 6% to over 50%. This high quantum yield nanosheets is applied for a down-conversion LED device and a 13% quantum yield is achieved. The up-conversion properties of carbon quantum dots and the low temperature spectrum of gallium oxide with doped by titanium also been studied.

Committee: Liangfeng Sun Ph.D (Advisor); Irina Stakhanova Ph.D (Other); Mikhail Zamkov Ph.D (Committee Member); Peter Lu Ph.D (Committee Member) Subjects: Materials Science; Nanoscience; Optics

Master of Science (MS), Bowling Green State University, 2018, Physics

Highly luminescent few-atoms thick colloidal PbS nanosheets are a promising material for the applications in infrared optoelectronics and photonics since a large in-plane charge carrier mobility and a tunable energy gap are unified in a single material. The time-resolved photoluminescence of the excitons in the nanosheets shows two distinguished fast and slow decays, which is very different from the quantum dots. The slow decay might be due to the exciton recombination after exciton migration or dissociation. The time-resolved photoluminescence spectroscopy studies show that there is a significant redshift of the emission spectrum later after excitation. This time-dependent photoluminescence spectrum indicates the possible migrations of excitons from thin parts (large energy gaps) of the nanosheets to thick parts (small energy gaps) due to the motion of the charge carriers, or possible Forster resonance energy transfer (FRET) from a thin nanosheet to a thicker one. The shift of the emission spectrum occurs within 500 to 700 nanoseconds, indicating the average time of the exciton-migration or FRET is at the same scale. As a side project of this thesis, the electric dipole moment of a typical PbSe quantum dot in the reaction solution is derived. This helped in the calculation of the dipole-dipole interaction energy of the quantum dots to explain the growth mechanism of PbSe nanorods. Another side project of this thesis was focused on the calculation of the energy gap of the carbon dots consisting amide groups. The calculated energy gap is close to one of the energy gaps measured by optical absorption. It helped to understand the light-emitting mechanism of the carbon dots.

Committee: Liangfeng Sun (Advisor); Alexey Zayak (Committee Member); Haowen Xi (Committee Member) Subjects: Physics

Master of Science (MS), Bowling Green State University, 2016, Physics

Colloidal nanomaterials have been of great interest due to their unique optoelectronic properties. The shape and size tuning of the nanomaterials at nanometer scale results in novel optical and electronic properties. Due to a high conductivity and large multiple exciton generations, PbSe nanorods are considered great for optoelectronic applications. We have developed a procedure for nanorods synthesis. TEM images, photoluminescence, absorption and PL lifetime peaks show that the rods produced are of high quality. We have studied the role of temperature and growth time on size tuning of PbSe nanorods. We have also studied the effect of the amount of chloroalkane, the ratio of oleic acid to lead, the amount of acetic acid and water on PbSe nanorods.

Committee: Liangfeng Sun (Advisor); Mikhail Zamkov (Committee Member); Lewis Fulcher (Committee Member) Subjects: Nanoscience; Physics

Master of Science (MS), Bowling Green State University, 2015, Physics

Colloidal nanostructured materials are promising for applications in optoelectronic devices. Beyond size-tuning as in quantum dots, shape-tuning of the material at the nanometer scale also results in novel optical and electronic properties. The applications demand high quality and structure-well-controlled materials, which is still underdeveloped. We have synthesized PbSe nanorods in wide temperature range 110-170 °C and different growth times from 25 sec to 5.5 minutes. Here we report the effect of chloroalkane co-solvent which is added during the synthesis drives the one dimensional growth of nanocrystals to form nanorods. It is seen that growth time and growth temperature also plays an important role on the control over size of nanorod formed. The photoluminescence, absorption and TEM measurements done on different samples taken at different reaction conditions shows that we have good control over size. The single exponential decay of PL life time for these rods indicates the high quality rods can be synthesized by this procedure.

Committee: Liangfeng Sun Dr. (Advisor); Mikhail Zamkov Dr. (Committee Member) Subjects: Physics