Bandgap Engineering of UV-Luminescent NanomaterialsBandgap Engineering of UV-Luminescent NanomaterialsLeah Bergman, University of Idaho, Leah Bergman, University of Idaho, DMR CAREER 0238843DMR CAREER 0238843

3 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8

PL In

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PL Energy (eV)

3.25

3.3

3.35

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3.45

3.5

0 4 8 12 16 20 24 28P

L E

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Mg Concentration (at.%)

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• One of the main advantages of a nanomaterial is size dependent properties, e.g., the tuneability of its light emission energy as a function of size: by the choice of nanoparticle size a semiconductor can be tuned to emit light at a desirable energy. An additional way to engineer the luminescence is via alloying. Our recent research effort focuses on the synthesis of MgxZn1-xO nanoalloys and on studies concerning their optical and structural properties. The objective is to achieve new luminescence lines as a function of both the alloy composition (x) and the crystallite size.

• Due to its deep exciton level and environmentally friendly chemical nature ZnO is emerging as a material of choice for stable UV-optical applications. ZnO has bandgap ~ 3.4 eV while MgO has bandgap ~ 7.5 eV; thus the MgxZn1-xO alloy system may provide a new optically tunable family of wide-bandgap materials.

• We grew MgxZn1-xO nanoalloys at Mg composition range 0-26% via thermal decomposition in a quartz tube furnace. The TEM analyses of the alloys (Fig. 1) indicate that the average crystallite size is ~ 30 nm and that it has wurtzite hexagonal crystal structure. The photoluminescence (PL) studies (Figs. 2 and 3) indicate that energy blueshift up to ~ 0.25 eV was achieved at the Mg composition range 0-26%. A first-principle calculation of confinement effect in ZnO crystallites indicates that a size less than 10 nm is needed in order so see any effect on the luminescence energy.

• Future work and significance: 1) Reduction of the alloy crystallite size and synthesis of nanoalloys

at the entire Mg composition range. 2) Doping issues at the nanoscale (see results in Notes Page).

The objectives are to achieve novel nanomaterials of deeper UV luminescence lines that potentially can be used in organic electroluminescence displays, and as cost-effective UV luminescent materials for various optoelectronics applications.

Fig. 1 The TEM image of the5% nanoalloy.TEM work in collaborationwith Dr. Tsvetanka Zheleva US Army Research Lab .

Fig. 3 The PL energy as a function of Mg composition. The error bars represent the spatial fluctuation of the PL energy and composition.

Bandgap Engineering of UV-Luminescent Nanomaterials Bandgap Engineering of UV-Luminescent Nanomaterials Leah Bergman, University of Idaho, Leah Bergman, University of Idaho, DMR CAREER 0238843DMR CAREER 0238843

Education:• The graduate students who are currently involved and supported via

this grant are John L. Morrison and Heather Hoeck. Additionally four undergraduates are supported via this grant and are actively taking part in the research. The students attend each year the Materials Research Society and American Physical Society conferences where they present their research.

• 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.

• The PI expends extensive effort in mentoring undergraduates and preparing them as future researchers in the University of Idaho as well as other universities or industry; three of the PI’s current graduate students were previously undergraduate research assistants in the group.

• The NSF funds have greatly contributed to the entire scope of research efforts of Dr. Leah Bergman. It has enabled an upgrade of the UV Photoluminescence and Raman Lab to include experimental setups to conduct optical studies at extreme environmental conditions of temperature and pressure* as well as the establishment of a new lab dedicated to the synthesis of novel luminescent nanomaterials.

* Chen, Purdy, Bergman et al., “Temperature response and anharmonicity of the optical phonons in GaN nanowires”, J. of Appl. Phys. 98, 026106 2005. Also selected for the Augs.05 Issue of Virtual Journal of Nanoscale Science and Technology (AIP, APS).

Outreach:The PI and her graduate student, Heather Hoeck, initiated contact with the Inland Empire Girl Scouts of America. This organization held an “Expanding Your Horizons Conference” in Spring 2005 in Spokane WA. This yearly conference was developed by the Math/Science Network in 1974. The Math/Science Network consists of women scientists, and its purpose is to educate young women about opportunities in the math and science fields and hopefully to improve enrollment of women in these fields.Heather was on the conference organizing committee, and participated in the conference as a speaker and a demonstrator as can be seen in the photograph.