Fast photoemissive probes for shock compression spectroscopy

Christensen, James Matthew

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https://hdl.handle.net/2142/104819 Copy

Description

Title

Fast photoemissive probes for shock compression spectroscopy

Author(s)

Christensen, James Matthew

Issue Date

2019-04-15

Director of Research (if dissertation) or Advisor (if thesis)

Dlott, Dana D.

Doctoral Committee Chair(s)

Dlott, Dana D.

Committee Member(s)

• Suslick, Kenneth
• Murphy, Catherine
• Vura-Weis, Joshua

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

Fluorescent probes, Shock Compression, Spectroscopy

Abstract

Fast photoemissive probes of two different varieties were designed and their behavior under shock compression was explored. The first probe was dye-doped silica microspheres, which were found to have 3.5× improved emission intensity under steady-state irradiation than the same dye in solution. When the dye-doped microspheres are embedded in polymer and subjected to planar shock compression, the photoemission redshifts and loses intensity. The dye emission redshift tracks the local density during shock. In free dye samples the shock-induced intensity loss is significantly slower than the redshift. It was found that when the dye is encapsulated in the silica microspheres, the time dependence of the shock-induced intensity loss matched the redshift almost exactly. Since it is easier to make intensity-change measurements rather than spectral-shift measurements, the dye-doped silica microspheres are a significant improvement in sensors to monitor shock compression of microstructured materials. The second probe developed is based upon CdTe or CdSe quantum dots (QDs). The small size of QDs, their size-tunable narrow photoemission, broad absorption, and fast radiative rate make them attractive candidates for probing heterogeneous materials. We have investigated the time-resolved photoemission response of QDs to shock compression in both homogeneous and heterogeneous films. It was found that CdSe QDs exhibited a redshift when axially compressed during shock, as opposed to a blueshift when hydrostatically compressed. When composite films of QD-doped silica microspheres and QD-doped polymer were subjected to shock compression, it was found that the photoemission exhibited two distinct peaks, with independent redshift and intensity-loss behavior, each having their own time dependence. This represents a significant advance for probing the interiors of microstructured materials using shock compression spectroscopy.

Graduation Semester

2019-05

Type of Resource

text

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http://hdl.handle.net/2142/104819

Copyright and License Information

Copyright 2019 James Christensen

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