Professional Education

  • Master of Arts, University of California Santa Barbara (2015)
  • Doctor of Philosophy, University of California Santa Barbara (2018)

All Publications

  • Bright infrared to ultraviolet and visible upconversion in small alkaline earth-based nanoparticles with biocompatible CaF2 shells. Angewandte Chemie (International ed. in English) Fischer, S., Siefe, C., Swearer, D. F., McLellan, C. A., Alivisatos, A. P., Dionne, J. A. 2020


    Upconverting nanoparticles (UCNPs) are promising candidates for photon-driven reactions, including light-triggered drug delivery, photodynamic therapy, and photocatalysis. Here, we investigate the NIR to UV and visible emission of sub-15 nm alkaline-earth rare-earth fluoride UCNPs (M 1-x Ln x F 2+x, MLnF) with a CaF 2 shell. We synthesize 8 alkaline-earth host materials doped with Yb 3+ and Tm 3+ , with alkaline-earth (M) spanning Ca, Sr, and Ba, MgSr, CaSr, CaBa, SrBa, and CaSrBa. We explore UCNP composition, size, and lanthanide doping dependent emission, focusing on upconversion quantum yield (UCQY) and UV emission. UCQY values of 2.46% at 250 W/cm 2 are achieved with 14.5 nm SrLuF@CaF 2 particles, with 7.3% of total emission in the UV. In 10.9 nm SrYbF:1%Tm 3+ @CaF 2 particles, UV emission increased to 9.9% with UCQY at 1.14%. We demonstrate dye degradation under NIR illumination using SrYbF:1%Tm 3+ @CaF 2 , highlighting the efficiency of these UCNPs and their ability to trigger photoprocesses.

    View details for DOI 10.1002/anie.202007683

    View details for PubMedID 32841471

  • Optimizing the formation of depth-confined nitrogen vacancy center spin ensembles in diamond for quantum sensing PHYSICAL REVIEW MATERIALS Eichhorn, T. R., McLellan, C. A., Jayich, A. 2019; 3 (11)
  • Sub-20 nm Core-Shell-Shell Nanoparticles for Bright Upconversion and Enhanced Forster Resonant Energy Transfer. Journal of the American Chemical Society Siefe, C., Mehlenbacher, R. D., Peng, C. S., Zhang, Y., Fischer, S., Lay, A., McLellan, C. A., Alivisatos, A. P., Chu, S., Dionne, J. A. 2019


    Upconverting nanoparticles provide valuable benefits as optical probes for bioimaging and Forster resonant energy transfer (FRET) due to their high signal-to-noise ratio, photostability, and biocompatibility; yet, making nanoparticles small yields a significant decay in brightness due to increased surface quenching. Approaches to improve the brightness of UCNPs exist but often require increased nanoparticle size. Here we present a unique core-shell-shell nanoparticle architecture for small (sub-20 nm), bright upconversion with several key features: (1) maximal sensitizer concentration in the core for high near-infrared absorption, (2) efficient energy transfer between core and interior shell for strong emission, and (3) emitter localization near the nanoparticle surface for efficient FRET. This architecture consists of beta-NaYbF4 (core) @NaY0.8-xErxGd0.2F4 (interior shell) @NaY0.8Gd0.2F4 (exterior shell), where sensitizer and emitter ions are partitioned into core and interior shell, respectively. Emitter concentration is varied (x = 1, 2, 5, 10, 20, 50, and 80%) to investigate influence on single particle brightness, upconversion quantum yield, decay lifetimes, and FRET coupling. We compare these seven samples with the field-standard core-shell architecture of beta-NaY0.58Gd0.2Yb0.2Er0.02F4 (core) @NaY0.8Gd0.2F4 (shell), with sensitizer and emitter ions codoped in the core. At a single particle level, the core-shell-shell design was up to 2-fold brighter than the standard core-shell design. Further, by coupling a fluorescent dye to the surface of the two different architectures, we demonstrated up to 8-fold improved emission enhancement with the core-shell-shell compared to the core-shell design. We show how, given proper consideration for emitter concentration, we can design a unique nanoparticle architecture to yield comparable or improved brightness and FRET coupling within a small volume.

    View details for DOI 10.1021/jacs.9b09571

    View details for PubMedID 31592655

  • Extending the Quantum Coherence of a Near-Surface Qubit by Coherently Driving the Paramagnetic Surface Environment PHYSICAL REVIEW LETTERS Bluvstein, D., Zhang, Z., McLellan, C. A., Williams, N. R., Jayich, A. 2019; 123 (14): 146804


    Surfaces enable useful functionalities for quantum systems, e.g., as interfaces to sensing targets, but often result in surface-induced decoherence where unpaired electron spins are common culprits. Here we show that the coherence time of a near-surface qubit is increased by coherent radio-frequency driving of surface electron spins, where we use a diamond nitrogen-vacancy (NV) center as a model qubit. This technique is complementary to other methods of suppressing decoherence and, importantly, requires no additional materials processing or control of the qubit. Further, by combining driving with the increased magnetic susceptibility of the double-quantum basis, we realize an overall fivefold sensitivity enhancement in NV magnetometry. Informed by our results, we discuss a path toward relaxation-limited coherence times for near-surface NV centers. The surface-spin driving technique presented here is broadly applicable to a wide variety of qubit platforms afflicted by surface-induced decoherence.

    View details for DOI 10.1103/PhysRevLett.123.146804

    View details for Web of Science ID 000489041300009

    View details for PubMedID 31702182

  • Optically Robust and Biocompatible Mechanosensitive Upconverting Nanoparticles ACS CENTRAL SCIENCE Lay, A., Sheppard, O. H., Siefe, C., McLellan, C. A., Mehlenbacher, R. D., Fischer, S., Goodman, M. B., Dionne, J. A. 2019; 5 (7): 1211–22
  • Hyperfine-enhanced gyromagnetic ratio of a nuclear spin in diamond NEW JOURNAL OF PHYSICS Sangtawesin, S., McLellan, C. A., Myers, B. A., Jayich, A., Awschalom, D. D., Petta, J. R. 2016; 18
  • Patterned Formation of Highly Coherent Nitrogen-Vacancy Centers Using a Focused Electron Irradiation Technique NANO LETTERS McLellan, C. A., Myers, B. A., Kraemer, S., Ohno, K., Awschalom, D. D., Jayich, A. 2016; 16 (4): 2450–54


    We demonstrate fully three-dimensional and patterned localization of nitrogen-vacancy (NV) centers in diamond with coherence times in excess of 1 ms. Nitrogen δ-doping during chemical vapor deposition diamond growth vertically confines nitrogen to 4 nm while electron irradiation with a transmission electron microscope laterally confines vacancies to less than 450 nm. We characterize the effects of electron energy and dose on NV formation. Importantly, our technique enables the formation of reliably high-quality NV centers inside diamond nanostructures with applications in quantum information and sensing.

    View details for DOI 10.1021/acs.nanolett.5b05304

    View details for Web of Science ID 000374274600048

    View details for PubMedID 27010642

  • Fabrication of organic thin-film transistors by spray-deposition for low-cost, large-area electronics ORGANIC ELECTRONICS Azarova, N. A., Owen, J. W., McLellan, C. A., Grimminger, M. A., Chapman, E. K., Anthony, J. E., Jurchescu, O. D. 2010; 11 (12): 1960–65