Single photon emission from ZnO nanoparticles

Abstract

Room temperature single photon emitters are very important resources for photonics and emerging quantum technologies. In this work we study single photon emission from defect centers in 20 nm zinc oxide (ZnO) nanoparticles. The emitters exhibit bright broadband fluorescence in the red spectral range centered at 640 nm with polarized excitation and emission. The studied emitters showed continuous blinking, however, bleaching can be suppressed using a polymethyl methacrylate (PMMA) coating. Furthermore, hydrogen termination increased the density of single photon emitters. Our results will contribute to the identification of quantum systems in ZnO.Sources of non-classical light, are important for a range of applications in quantum communications, sensing and information processing 1, 2 . A particular emphasis is placed on the development of solid-state single photon sources that operate at room temperature, as those are the most promising sources for scalable and integrated devices. Color centers in diamond 3 , and in particular the nitrogen vacancy 4 and the silicon vacancy defects 5,6 , have been the subject of intense study in recent years due to their unprecedented photostability and spin properties. Recently, several additional materials have emerged as candidates for single photon generation, including site controlled GaN quantum dots 7 , defects in silicon carbide 8 and zinc oxide (ZnO) 9 . While the single photon emission in SiC is attributed to the intrinsic defect known as an "antisite -vacancy pair", the origin of the quantum emission in ZnO remains under debate. ZnO offers an interesting and valuable system to study quantum effects at the nanoscale 10 . ZnO nanoparticles are commercially available while nanowires and other nanostructures can be easily synthesized by hydrothermal 11 or chemical vapour deposition growth techniques 12,13 . In addition, ZnO is very suitable for photonic applications, as it has a wide, direct bandgap (3.4 eV) and a large number of intrinsic defects and impurities that emit from the ultraviolet to the near infrared 14,15 . Finally, photonic elements including microdisk cavities 11,16,17 can be easily fabricated from this material. Therefore, there is an urgency to understand and

Zinc Oxide Nanophotonics

“…SPSs in ZnO defects are advantageous in terms of its visibility and stability. It has been shown that the red fluorescence of ZnO defect center is almost fully linearly polarized with high visibility (~85%) [8]. This is highly beneficial for employing SPSs for quantum communications as the information is encoded in the polarization state of the emitter.…”

“…The calculated decay rates correspond to radiative lifetimes ranging from 1 to 5 ns and non-radiative lifetimes ranging from 40 to 429 ns, respectively. Choi et al showed that only 10% of the observed emitters showing strong bunching behavior and emission from those defects was associated with a very narrow emission line [8]. However, Jungwirth et al showed that 7 of the 14 nanoparticle-based defects studied displayed signs of bunching and one of the five sputtered film defects exhibited bunching [10].…”

“…This is highly beneficial for employing SPSs for quantum communications as the information is encoded in the polarization state of the emitter. Furthermore, observed ZnO single emitters were stable for the duration of the measurement (∼10 mins) [8], which is important for future quantum photonic applications [54]. The long-term optical stability of SPSs in ZnO is still under investigation, with some works suggesting blinking, while others found photostable emitters.…”

“…Morfa et al [9] first reported the generation of single-photon emission and antibunching, bunching, and spectral measurements from ZnO defects characterized in confocal microscope at room temperature. Subsequently, single-photon emission from ZnO nanoparticles was demonstrated in 2014 by two other groups [8,10]. (A) Schematic of confocal microscope used to probe single defects.…”

“…Thus, the need to characterize defects in ZnO is further amplified with the recent applications of ZnO as hosts of SPSs for quantum technologies [8][9][10] and their use in random lasing and other advanced sensing technologies [11]. SPSs that generate nonclassical states of light have been extensively explored over the past decade due to a variety of applications, including quantum cryptography, quantum computation, and metrology [12][13][14].…”