Rare earth (RE) doped GaN nanowires (NWs), combining the well-defined and controllable optical emission lines of trivalent RE ions with the high crystalline quality, versatility and small dimension of the NW host, are promising building blocks for future nanoscale devices in optoelectronics and quantum technologies. Europium doping of GaN NWs was performed by ion implantation and structural and optical properties were assessed in comparison to thin film reference samples. Despite some surface degradation for high implantation fluences, the NW core remains of high crystalline quality with lower concentrations of extended defects than observed in ion implanted thin films. Strain introduced by implantation defects is efficiently relaxed in NWs and the measured deformation stays much below that in thin films implanted in the same conditions. Optical activation is achieved for all samples after annealing and, while optical centres are similar in all samples, Eu 3+ emission from NW samples is shown to be less affected by residual implantation damage than for the case of thin films. The incorporation of Eu in GaN NWs was further investigated by nano-cathodoluminescence and X-ray absorption spectroscopy (XAS). Maps of the Eu-emission intensity within a single NW agree well with the Eu-distribution predicted by Monte Carlo simulations suggesting that no pronounced Eu-diffusion takes place. XAS shows that 70-80% of Eu is found in the 3+ charge state while 20-30% is 2+ attributed to residual implantation defects. A similar local environment was found for Eu in NWs and thin films: for low fluences, Eu is mainly incorporated on substitutional Ga-sites while for high fluences XAS points at the formation of a local EuN-like next neighbour structure. Results reveal the high potential of ion implantation as a processing tool at the nano-scale.
Al x Ga 1−x N alloys, covering the entire compositional range (0 ≤ x ≤ 1), were implanted at room temperature with 200 keV argon (Ar) ions to fluences ranging from 1 × 10 13 to 2 × 10 16 Ar/cm 2 . The damage formation mechanisms and radiation resistance of Al x Ga 1−x N alloys were investigated combining in situ Rutherford backscattering spectrometry/channeling (RBS/C) and ex situ X-ray diffraction (XRD) in order to assess the damage profiles and the elastic response of the material to radiation. For all compounds, damage buildup proceeds in four stages revealing a saturation of the defect level for high fluences without any sign of amorphization. Surprisingly, in this high fluence regime, RBS/C reveals higher defect levels in samples with high AlN concentrations in contrast to the common believe that AlN is more radiation resistant than GaN. A model is proposed ascribing this behavior to a lower defect recombination cross section at room temperature combined with the formation of stable extended defects. The processes are probably dependent on the collision cascade density, that is, the mass of the implanted ions. XRD shows that implantation leads to the incorporation of large lattice strain in the implanted layer which increases with increasing fluence. Above a threshold fluence, an abrupt change of the elastic properties of the crystals is observed and strain saturates in the entire implanted region. This threshold fluence is reached earlier for GaN than for Al x Ga 1−x N alloys with x > 0.
A series of fluorescent sensor molecules based on a phosphane sulfide derivative that is soluble in an organoaqueous solvent were designed and synthesized. The structure of the fluorophore has been optimized in order to have the best compromise in terms of solubility and photophysical properties. The obtained properties are in full agreement with quantum chemical calculations. A fluorescent molecular sensor containing one polyoxoethylene group has been synthesized and an efficient quenching upon mercury complexation has been observed. Finally, this sensing molecule has been introduced in a microfluidic chip in which fluorescence detection has been integrated. An efficient fluorescence response was observed upon mercury addition.
A detailed spectroscopic analysis of Eu3+ implanted and annealed AlN nanowires (NWs) grown by plasma-assisted molecular beam epitaxy is presented by using micro-Raman, temperature-dependent steady-state photoluminescence, and time-resolved photoluminescence. Two different annealing temperatures (1000 °C and 1200 °C) were used. Such annealing conditions achieved a recovery of the original AlN crystalline structure as confirmed by Raman analysis. For both samples, the red Eu3+ intra-4f 6 luminescence was demonstrated, where the 5D0 → 7F2 transition at 624 nm is the most intense. Two well-resolved Eu optically active centers were observed in the present AlN NWs and designated as Eu1 and Eu2, due to their similar spectral shape when compared to those observed in GaN layers [Bodiou et al., Opt. Mater. 28, 780 (2006); Roqan et al., Phys. Rev. B 81, 085209 (2010)]. Their behavior was found to depend on the annealing temperature. Photoluminescence studies reveal that at 14 K, Eu2 is dominant for the lower annealing temperature, while Eu1 is dominant for the highest annealing temperature. Moreover, at room temperature, Eu1 center was found to be the dominant for both samples. Indeed, the luminescence intensity of the 5D0 → 7F2 transition exhibits a lower thermal quenching for the samples annealed at the highest temperature (∼80% for the sample annealed at 1200 °C and ∼50% for the sample annealed at 1000 °C) boosting their potential use as efficient red emitters.
In this work, Eu 3+ -implanted and annealed AlxGa1-xN (0 ≤ x ≤ 1) nanowires (NWs) grown on GaN NW template on Si (111) substrates by plasma-assisted molecular beam epitaxy are studied by µ-Raman, cathodoluminescence (CL), nano-CL, and temperature-dependent steady-state photoluminescence. The preferential location of the Eu 3+ -implanted ions is found to be at the AlxGa1-xN top-section. The recovery of the as-grown crystalline properties is achieved after rapid thermal annealing (RTA). After RTA, the red emission of the Eu 3+ ions is attained for all the samples with below and above bandgap excitation. The 5 D0 → 7 F2 transition is the most intense one, experiencing a redshift with increasing AlN nominal content (x) from GaN to AlN NWs. Moreover, AlN nominal content and annealing temperature alters its spectral shape suggesting the presence of at least two distinct optically active Eu 3+ centers (Eu1 and Eu2). Thermal quenching of the Eu 3+ ion luminescence intensity, I, is found for all the samples from 14 K to 300 K, being the emission of Eu 3+ -implanted AlN NWs after RTA at 1200 ℃ the most stable (I300 K/I14 K ~80%). The GaN/AlN interface in this sample is also found to have a key role in the Eu 3+ optical activation.
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