Controlling the photoluminescence of quantum emitters in hexagonal boron nitride by external magnetic fields

Abstract

The recent observation of room temperature spin-dependent photoluminescence (PL) emission from hexagonal boron nitride’s (h-BN’s) defect centers motivates for performing a complementary low-temperature photophysical study of quantum emitters under relatively high magnetic fields. Here, we investigate the PL emission dynamics of h-BN’s visible single-photon emitters under an applied out-of-plane magnetic field at cryogenic temperatures. The PL intensity of the emitters in our work strikingly exhibits strong magnetic field dependence and decreases with the increased magnetic field. A substantial decrease in the integrated PL intensity of the emitters by up to one order of magnitude was observed when the applied field is increased from 0T to 7T. The observed reversible photodarkening of PL emission due to the applied magnetic field is in very well agreement with the predictions of a recent joint experimental and theoretical study and can happen only if the spin-selective, non-radiative, and asymmetric intersystem crossing transitions proceed from the triplet excited state to the lowest-lying spin-singlet metastable state and from the metastable state to the triplet ground state. Our results not only shed more light on the light emission paths of defect centers in h-BN but also show the use of the magnetic field as an efficient control knob in the development of magneto-optical devices.

Boron and Nitrogen Isotope Effects on Hexagonal Boron Nitride Properties

“…[13] We have previously demonstrated that the properties of hBN can be varied by controlling its concentrations of boron isotopes. There are two stable boron isotopes, which are naturally distributed at ≈20% 10 B and 80% 11 B. These isotopes have distinctly different properties.…”

“…These isotopes have distinctly different properties. Their nuclear spins are 3/2 and 3 for 10 B and 11 B respectively. 10 B has one of the largest neutron capture cross sections of any isotope of any element, ≈3855 barns for neutrons with velocities of 2200 m −1 s. [14] For the majority of element isotopes, the neutron capture cross section is on the order of one or less.…”

“…Vuong et al [17] demonstrated that the energy band gap of hBN was slightly reduced or increased when enriched in 10 B or 11 B, respectively. The E 2g high peak position in the Raman spectra shifted up from 1366 cm −1 for hBN with the natural distribution of boron isotopes to 1393 cm −1 for h 10 BN and down to 1357 cm −1 for h 11 BN, [17][18][19] The FWHM of the E 2g high peak at room temperature of the boron monoisotopic hBN was also reduced to 3.0 from 7.5 cm −1 for natural hBN, due to less isotopic disorder. [19] The maximum peak width was predicted to occur with isotope concentrations of 65% 11 B and 35% 10 B.…”

“…[9] hBN is appealing for quantum devices due to its ability to host bright, stable, single photon emitters, some of which are magnetically addressable. [10,11] Boron nitride is also an excellent platform for near-zero index photonics in the infrared. [12] Near-zero-index materials exhibit unique features in the area of light-matter interaction: when the values of the relative permittivity reach zero, at the operating frequency, the wavelength in these media is "stretched," and the phase of the signal is approximately uniform across this structure, which shapes the time oscillating waves to a static-like spatial distribution.…”

“…The first step, termed ingot formation, was done to purify the source materials and thoroughly mix them into an isotropic solution without any nitrogen. Isotopically pure (>99%) 10 B or 11 B powder was mixed with Ni and Cr powder in an alumina crucible in the mass ratio 12/12/1 Ni/Cr/B, respectively. This was then placed in a horizontal tube furnace, evacuated of air, and purged with a mixture of 93/7 argon/hydrogen flowing continuously at 270 sccm and 850 torr.…”