Papers by Keyword: Color Centers

Abstract: Point defects in 4H silicon carbide (4H-SiC), such as the silicon vacancy, also known as color centers, offer considerable potential for quantum applications in the fields of quantum sensing as well as computing and communication. The latter two necessitate indistinguishable photons for entanglement swapping and consequently demand precise control over the electronic transition energies, i.e. emission and absorption wavelengths of color centers. One way to achieve this is through monolithic integration of electronic devices in combination with integrated photonics in 4H-SiC. This is considered a potential pathway for scalable quantum photonic integrated circuits. In this paper, we investigate the suitability of a signal-ground-modulator and a vertical pin diode in combination with a waveguide to (i) achieve local field strengths of 5 to 20 MV/m in the crystal’s c-direction, (ii) stabilize the charge state of the silicon vacancy by controlling the local Fermi level, (iii) meet the requirements for photonic single-mode operation, and (iv) minimize the absorption of the evanescent wave due to metal contacts. The findings of the electronic and optical simulations conducted with Synopsys Sentaurus and Ansys Lumerical suggest that the signal-ground-modulator, commonly used in integrated photonics, rarely attains the requisite field strength. In contrast, the vertical pin diode has the potential to meet these requirements even at reduced bias voltages. Furthermore, the intrinsic layer of the diode offers a wide region in which to host the color center in its optically active, negatively charged state.

Abstract: Experiments were carried out in which the luminescence of color centers in lithium fluoride crystals was excited by two different femtosecond lasers with significantly different energies, durations and pulse repetition rates. It was established that in all experiments the main center, the luminescence of which was excited nonlinearly, was the F₃⁺ color center. Unusual experimental data were obtained; a laser with low pulse energy (4 nJ) excited triplet luminescence of these centers (570 nm) but did not excite singlet luminescence (540 nm). Another laser with a higher pulse energy (0.3 mJ), on the other hand, excited singlet luminescence and did not excite triplet luminescence. A proposed diagram of energy levels and quantum transitions is presented, explaining the possible mechanisms of nonlinear excitation of luminescence in these experiments.

Abstract: Point defects in silicon carbide (SiC) are well positioned for integration with SiC based quantum photonic devices due to the maturity of SiC material and fabrication technology, the plethora of candidate quantum emitters that can be formed in SiC, and the potential for emission over a wide spectral range from the visible to the infrared. However, for each of the available color centers in SiC, only one of the charge states has displayed quantum emission, meaning that the emission strongly depends on the Fermi level and hence the doping concentration in the material. In this contribution, we discuss the methodology and mechanism for electrical charge-state control over point defects in SiC devices.

Abstract: Lithium fluoride (LiF) is a well-known dosimeter material and is sensitive to any kind of ionizing radiation. A linear accelerator for protontherapy under development at ENEA C.R. Frascati was used to irradiate LiF crystals and thin films at room temperature with proton beams of 3 and 7 MeV energy in a dose range from 10³ to 10⁷ Gy. The irradiation of LiF induced the formation of stable F₂ and F₃⁺ color centers (CCs), which emit with broad photoluminescence (PL) bands under optical pumping at wavelengths close to 450 nm. By acquiring the PL image of the irradiated spots with a conventional fluorescence microscope, the transversal proton beam intensity was mapped with a high spatial resolution. The integrated PL intensity was also measured as a function of the irradiation dose: LiF films showed a linear PL response extending over three orders of magnitude of dose range, independently on the beam energy. It was also possible to measure the CCs PL distribution with proton penetration depth and direct imaging the Bragg peak, which gives an estimation of the proton beam energy. The sensitivity of the optical reading techniques and the high emission efficiency of CCs provided encouraging results to use photoluminescent color-center LiF-based radiation detectors for proton beam dosimetry and imaging applications.

Abstract: The present paper is devoted to the study of the kinetics of luminescence flash in LiF-WO₄ crystals and development of the model to describe the kinetics of cathodoluminescence growth under pulsed excitation.