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   https://doi.org/10.1063/1.5097780  

   Hilfiker, Matthew ; Kilic, Ufuk ; Mock, Alyssa ; Darakchieva, Vanya ; Knight, Sean ; Korlacki, Rafał ; Mauze, Akhil ; Zhang, Yuewei ; Speck, James ; Schubert, Mathias ( June 2019 , Applied Physics Letters)
2. Anisotropy, phonon modes, and lattice anharmonicity from dielectric function tensor analysis of monoclinic cadmium tungstate

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   Mock, A. ; Korlacki, R. ; Knight, S. ; Schubert, M. ( April 2017 , Physical Review B)
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5. Elevated temperature spectroscopic ellipsometry analysis of the dielectric function, exciton, band-to-band transition, and high-frequency dielectric constant properties for single-crystal ZnGa 2 O 4

   https://doi.org/10.1063/5.0087623  

   Hilfiker, Matthew ; Williams, Emma ; Kilic, Ufuk ; Traouli, Yousra ; Koeppe, Nate ; Rivera, Jose ; Abakar, Assya ; Stokey, Megan ; Korlacki, Rafał ; Galazka, Zbigniew ; et al ( March 2022 , Applied Physics Letters)

   We report the elevated temperature (22 °C [Formula: see text]  T [Formula: see text] 600 °C) dielectric function properties of melt grown single crystal ZnGa₂O₄using a spectroscopic ellipsometry approach. A temperature dependent Cauchy dispersion analysis was applied across the transparent spectrum to determine the high-frequency index of refraction yielding a temperature dependent slope of 3.885(2) × 10⁻⁵ K⁻¹. A model dielectric function critical point analysis was applied to examine the dielectric function and critical point transitions for each temperature. The lowest energy M₀-type critical point associated with the direct bandgap transition in ZnGa₂O₄is shown to red-shift linearly as the temperature is increased with a subsequent slope of −0.72(4) meV K⁻¹. Furthermore, increasing the temperature results in a reduction of the excitonic amplitude and increase in the exciton broadening akin to exciton evaporation and lifetime shortening. This matches current theoretical understanding of excitonic behavior and critically provides justification for an anharmonic broadened Lorentz oscillator to be applied for model analysis of excitonic contributions.

    

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