Lukas Razinkovas

• Turiansky, Mark E.; Mu, Sai; Razinkovas, Lukas; Parto, Kamyar; Patel, Sahil D. & Doan, Sean [Show all 11 contributors for this article] (2025). Characterization of chromium impurities in β‐Ga2O3. Journal of Applied Physics. ISSN 0021-8979. 137(10). doi: 10.1063/5.0255859. Full text in Research Archive Show summary

  Chromium is a common transition-metal impurity that is easily incorporated during crystal growth. It is perhaps best known for giving rise to the 694.3 nm (1.786 eV) emission in Cr-doped Al2O3⁠, exploited in ruby lasers. Chromium has also been found in monoclinic gallium oxide, a wide-bandgap semiconductor being pursued for power electronics. In this work, we thoroughly characterize the behavior of Cr in Ga2O3 through theoretical and experimental techniques. β-Ga2O3 samples are grown with the floating zone method and show evidence of a sharp photoluminescence signal, reminiscent of ruby. We calculate the energetics of formation of Cr from first principles, demonstrating that Cr preferentially incorporates as a neutral impurity on the octahedral site. Cr possesses a quartet ground-state spin and has an internal transition with a zero-phonon line near 1.8 eV. By comparing the calculated and experimentally measured luminescence lineshape function, we elucidate the role of coupling to phonons and uncover features beyond the Franck–Condon approximation. The combination of strong emission with a small Huang–Rhys factor of 0.05 and a technologically relevant host material renders Cr in Ga2O3 attractive as a quantum defect.

• Silkinis, Rokas; Maciaszek, Marek; Žalandauskas, Vytautas; Bathen, Marianne Etzelmüller; Vines, Lasse & Alkauskas, Audrius [Show all 7 contributors for this article] (2025). Optical lineshapes of the C center in silicon from ab initio calculations: Interplay of localized modes and bulk phonons. Physical review B (PRB). ISSN 2469-9950. 111(12). doi: 10.1103/PhysRevB.111.125136. Full text in Research Archive
• Zhang, Xie; Turiansky, Mark E.; Razinkovas, Lukas; Maciaszek, Marek; Broqvist, Peter & Yan, Qimin [Show all 12 contributors for this article] (2024). First-principles calculations of defects and electron-phonon interactions: Seminal contributions of Audrius Alkauskas to the understanding of recombination processes. Journal of Applied Physics. ISSN 0021-8979. 135(15). doi: 10.1063/5.0205525. Full text in Research Archive Show summary

  First-principles calculations of defects and electron–phonon interactions play a critical role in the design and optimization of materials for electronic and optoelectronic devices. The late Audrius Alkauskas made seminal contributions to developing rigorous first-principles methodologies for the computation of defects and electron–phonon interactions, especially in the context of understanding the fundamental mechanisms of carrier recombination in semiconductors. Alkauskas was also a pioneer in the field of quantum defects, helping to build a first-principles understanding of the prototype nitrogen-vacancy center in diamond, as well as identifying novel defects. Here, we describe the important contributions made by Alkauskas and his collaborators and outline fruitful research directions that Alkauskas would have been keen to pursue. Audrius Alkauskas’ scientific achievements and insights highlighted in this article will inspire and guide future developments and advances in the field.

• Maciaszek, Marek & Razinkovas, Lukas (2024). Blue Quantum Emitter in Hexagonal Boron Nitride and a Carbon Chain Tetramer: a First-Principles Study. ACS Applied Nano Materials. 7(16), p. 18979–18985. doi: 10.1021/acsanm.4c02722. Full text in Research Archive Show summary

  Single-photon emitters in hexagonal boron nitride (h-BN) exhibit compelling optical properties, such as high brightness and photostability, making them promising candidates for applications in emerging nanophotonic and quantum technologies. However, their further progress would greatly benefit from the identification of their chemical nature, which in most cases is still under debate. Among the various emitters observed in h-BN, blue quantum emitters (435 nm), also known as B-centers, are unique not only due to their promising optical properties but also because they can be fabricated at specific locations via electron-beam irradiation. Herein, ab initio calculations are used to demonstrate that the properties of a carbon chain tetramer are in excellent agreement with the characteristics of blue quantum emitters. The calculated zero-phonon line (ZPL) energy (3.13 eV) and radiative lifetime (1.62 ns) of the carbon chain tetramer align well with experimental observations. The relatively weak electron–phonon coupling indicates intense emission at the ZPL, and the Debye–Waller factor of 0.25 is consistent with experimental data. We demonstrate that, despite the absence of an inversion center in the carbon chain tetramer, it exhibits a negligible linear Stark effect, consistent with experimental findings. Additionally, our hypothesis explains the experimental observation that the formation of blue emitters is only possible in samples containing numerous ultraviolet emitters, which are probably identical to carbon dimers.

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