Color centers in wide-bandgap semiconductors for subdiffraction imaging: a review

Stefania Castelletto; Alberto Boretti

doi:10.1117/1.AP.3.5.054001

Abstract

Solid-state atomic-sized color centers in wide-band-gap semiconductors, such as diamond, silicon carbide, and hexagonal boron nitride, are important platforms for quantum technologies, specifically for single-photon sources and quantum sensing. One of the emerging applications of these quantum emitters is subdiffraction imaging. This capability is provided by the specific photophysical properties of color centers, such as high dipole moments, photostability, and a variety of spectral ranges of the emitters with associated optical and microwave control of their quantum states. We review applications of color centers in traditional super-resolution microscopy and quantum imaging methods, and compare relative performance. The current state and perspectives of their applications in biomedical, chemistry, and material science imaging are outlined.

The resolution of common fluorescence microscopes (wide-field or confocal microscopes) is limited by the diffraction of light, known as the Abbe limit. The attainable resolution is given by the full-width at half-maximum (FWHM) of the point spread function (PSF) of the beam at the focus of the objective. A high numerical aperture ( $NA = 1.4$ ) objective with visible light ( $λ = 532 nm$ ) can theoretically reach a resolution of $d \approx λ / (2 \sqrt{2} \times NA) \sim 134 nm$ and $d \approx λ / (2 \times NA) \sim 190 nm$ for the confocal and wide field, respectively, whereas the experimental resolution is generally in the range of $\sim 200$ to 250 nm due to the sample optical properties and beam imperfections. Super-resolution fluorescence microscopy (SRM) permits us to beat the diffraction limit, and it obtains images with a higher resolution, from 100 nm to as low as 20 nm or, in some cases, even lower, with few nanometer localization in some cases. This is a resolution/localization possible only by electron scanning probe microscopes. SRM’s impact in life science, chemical, and physical sciences has been recognized by the Nobel Prize for Chemistry in 2014,1 and it has revolutionized many areas of cellular microscopy2 and even virology.3^,4