One of our recent research efforts focuses on the synthesis of MgxZn1-xO nanoalloys and on studies concerning their optical and material properties. The objective is to achieve new luminescence lines in the UV-range as a function of alloy composition, x.

MgxZn1-xO nanoalloys at composition range x = 0-0.6 were grown via thermal decomposition in a quartz tube furnace. Figure 1 presents a characteristic SEM image of the crystallites. The room-temperature photoluminescence (PL) studies indicate that energy blueshift up to ~1.0 eV was achieved, as is depicted in Figure 2. This is a significant shift; to put it in perspective, the human eye is sensitive to a ~ 1.5 eV range. To understand the origins of the PL and the spectral linewidth, low-temperature photoluminescence studies are currently being undertaken. Figure 3 presents the PL spectra of the ZnO and MgZnO at 80 K. Our preliminary results indicate that the PL of ZnO nanocrystallites is due to multiple excitonic emissions. The very broad linewidth of the alloy, even at this low temperature, may be due to inhomogeneities in the alloy composition and phase segregation.

Areas under investigation: • The assignment of the excitons of the ZnO nanocrystallites. • The compositional inhomogeneities and phase segregation of the nanoalloys. • Encapsulation of the nanocrystallites in UV transparent media. The long-term goals are to achieve novel, cost-effective, and environmentally friendly bandgap-engineered nanomaterials capable of UV luminescence at desired emission energies. These nanoalloys may have potential applications in photonics and electroluminescence display technologies.

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Figure 1. The SEM image of the nanocrystallites.The crystallites weresynthesized on Sisubstrate and have anaverage size ~ 30 nm.

Figure 2.The room-temperature PL spectra of the ZnO,Mg0.2Zn0.8O, and theMg0.6Zn0.4O. A blueshift of ~1.0 eV was achieved.

Figure 3.The PL spectra at 80 K of the ZnO(red) and Mg0.15Zn0.85O (blue). Even at that relatively low compositionthe linewidth of the alloy exhibits a significant broadening, masking the excitonic emission.

Ultraviolet Photoluminescence of MgZnO NanoalloysUltraviolet Photoluminescence of MgZnO Nanoalloys Leah Bergman Leah Bergman DMR CAREER 0238845DMR CAREER 0238845

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Education and Outreach:The graduate students who are currently involved and supported via this grant are John L. Morrison and Heather Hoeck. Additionally four undergraduates are actively taking part in the research: in particular Erin Casey is supported via this grant. The undergraduates are from Mechanical Engineering, Chemistry, and Physics. Dr. Bergman is dedicated to the involvement of undergraduates in research with the goal that they pursue higher education in the sciences. The graduate students attend various leading conferences on a yearly basis such as MRS and APS, and this year also a Gordon conference. Undergraduate students participate in MRS and APS as well on occasion. In these conferences the PI and students present their research and interact with other researchers.

The PI participates each summer in the NSF-REU as well as in the HOIST programs, the latter which is a program dedicated to involving Native American high school students in active research in the sciences. Additionally, the PI’s graduate student, Heather Hoeck, is involved with the Inland Empire Girl Scouts of America in initiatives concerning the involvement of young women in the math and science fields.

Ultraviolet Photoluminescence of MgZnO NanoalloysUltraviolet Photoluminescence of MgZnO Nanoalloys Leah Bergman Leah Bergman DMR CAREER 0238845DMR CAREER 0238845

Figure 2. Part of the PI’s group in the optical materials lab. From left to right: John Morrison (graduate), Russell Geisthardt (REU), Leah Bergman, Heather Hoeck (graduate), James Mitchell (undergrad), and Jesse Huso (graduate).

Figure 1. The PI with undergraduate student Erin Casey in the photoluminescence and Raman lab.