We describe the structural and electronic properties of graphene doped with substitutional impurities of 4d and 5d transition metals. The adsorption energies and distances for 4d and 5d metals in graphene show similar trends for the later groups in the periodic table, which are also well-known characteristics of 3d elements. However, along earlier groups the 4d impurities in graphene show very similar adsorption energies, distances and magnetic moments to the 5d ones, which can be related to the influence of the 4d and 5d lanthanide contraction. Surprisingly, within the manganese group, the total magnetic moment of 3 μ_B for manganese is reduced to 1 μ_B for technetium and rhenium. We find that compared with 3d elements, the larger size of the 4d and 5d elements causes a high degree of hybridization with the neighbouring carbon atoms, reducing spin splitting in the d levels. It seems that the magnetic adjustment of graphene could be significantly different if 4d or 5d impurities are used instead of 3d impurities.

In this work, we employed a novel microwave-assisted synthesis method to produce nitrogen and boron co-doped carbon dots (B–N co-doped CDs). To achieve optimal synthesis, we conducted a comprehensive parameter modulation approach, combining various synthesis temperatures, times, and precursor concentrations, while keeping the power constant at 150 W and pH 5. Using maximum fluorescence emission as our response variable, the best conditions were identified as 120 °C, 3 min, and a precursor concentration of 1 mg/mL. Characterization using field emission scanning electron microscopy revealed these CDs to have a spherical morphology with an average size of 10.9 ± 3.38 nm. Further high-resolution transmission electron microscopy showed an interplanar distance of 0.23 nm, which is in line with prior findings of CDs that present a 0.21 nm distance corresponding to the (100) plane of graphite. Optical properties were ascertained through UV–vis absorption, identifying distinct π–π* and n–π* transitions. Fluorescence spectroscopy highlighted an emission peak at 375 nm when excited at 295 nm, achieving a quantum yield of 56.7%. Fourier-transform infrared spectroscopy and Raman spectroscopy analyses confirmed the boronic acid and amine groups’ presence, underscoring the graphitic nature of the core and the co-doping of boron and nitrogen. These empirical observations were compared with theoretical investigations through simulated Raman spectra, proposing a potential structure for the CDs. X-ray photoelectron spectroscopy further endorsed the co-doping of nitrogen and boron, along with the detection of the specified functional groups. All these characteristics could lend this nanomaterial to different types of applications such as fluorescent probes for a broad range of analytes and for fluorescent cell imaging.

Within the framework of a self-consistent $spd$ tight-binding Hamiltonian and ab initio pseudopotential techniques we study the magnetic properties of small ${\mathrm{Co}}_N$, ${\mathrm{Ni}}_N$, ${\mathrm{Rh}}_N$, and ${\mathrm{Pd}}_N$ $(N=4-21)$ clusters having noncompact structures. Following the recently reported existence of a nonicosahedral growth for small Rh clusters, as well as the predicted high stability of open (biplanar) structures for the late $3d$ and $4d$ 13-atom transition metal clusters, we consider different growth sequences based in the atomic capping of small half-octahedral and tetrahedral cluster units, which can be considered in general as precursors of the lowest energy configurations reported by Bae et al. [Phys. Rev. B 70, 195413 (2004)] and Chang and Chou [Phys. Rev. Lett. 93, 133401 (2004)]. On the one hand, for noncompact unrelaxed ${\mathrm{Co}}_N$ and ${\mathrm{Ni}}_N$ clusters, which are elements characterized by a large exchange regime, we obtain a slowly decreasing average magnetization $⟨\mu ⟩$ with increasing the size of the clusters. In addition, for a given cluster size, the value of $⟨\mu ⟩$ for different isomers has been found to be determined in general by the average coordination number of the structures, i.e., less (more) coordinated structures have high (low) magnetization states due to $d$ band narrowing effects. On the other hand, for unrelaxed ${\mathrm{Rh}}_N$ and ${\mathrm{Pd}}_N$ structures, which are defined as weakly ferromagnetic systems, a complex decreasing oscillatory behavior is obtained with average magnetic moments per atom which are in general in reasonable agreement with the measured data. Interestingly, in the case of ${\mathrm{Rh}}_N$ clusters for $N⩾15$, the suggested biplanarlike structures are characterized by values of $⟨\mu ⟩$ of the order of $0.05{\mu }_{\mathrm{B}}∕\text{atom}$, in clear disagreement with experiment, a result that could be interpreted as the beginning of a different structural growth sequence where clusters need to rearrange themselves towards different structures with higher magnetization states. As expected, fully relaxed clusters leads to the existence of atomic configurations with a complex nonuniform distribution of interatomic distances that reduces in general the value of $⟨\mu ⟩$. We conclude that the normally observed oscillatory magnetization data in cluster systems could be induced by a growth behavior in which cluster geometries flip-flop between low and high symmetry atomic arrays.