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BaF 2 -based detectors have been used in many fields requiring fast timing, especially in positron annihilation lifetime (PAL) spectroscopy. The performance of a PAL spectrometer is closely correlated with the time response of BaF 2 -based detectors. Therefore, it is important to select scintillation detectors with excellent time resolution. In this work, the coincidence time resolution of BaF 2 -based H6610 detectors was investigated using a digital oscilloscope. The time response of detectors has been optimized by tuning the supply voltages, the sampling rate of the oscilloscope, and digital fraction constants, achieving a conicidence time resolution of about 162 ps for the 0.511 MeV annihilation γ-ray pairs and 108 ps for the 60 Co cascade γ-rays, respectively. Furthermore, a digital PAL spectrometer composed of two BaF 2 -based H6610 detectors and an oscilloscope was developed with a time resolution of around 130 ps, much better than most digital PAL spectrometers.

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Diluted magnetic semiconductors (DMSs) have numerous potential applications, particularly in spintronics. Therefore, the search for advanced DMSs has been a critical task for a long time. In this work, room-temperature ferromagnetism is observed in the C+-implanted AlN films with C+ doses of 5×1016 (AlN:C5×1016) and 2×1017 cm−2 (AlN:C2×1017). AlN:C2×1017 exhibits a saturation magnetization of ∼0.104 emu/g, nearly 1.5 times that of AlN:C5×1016. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) measurements reveal that the implanted C+ ions occupy the interstitial lattice sites and substitute at the sites of Al atoms. XPS and Doppler broadening of positron annihilation radiation measurements demonstrate the existence of the Al-vacancy related defects in the C+-implanted AlN films. First-principles calculations indicate that the ferromagnetism in AlN:C5×1016 and AlN:C2×1017 is mainly originated from defect complexes involving interstitial C atoms and Al vacancies, which have the lowest formation energy among AlN:C defects containing C atoms and Al vacancies. This work provides a feasible route to develop advanced DMSs.