Single domain Ni 3 N nitride particles are synthesized by simultaneous decomposition and nitridation in ammonia atmosphere of [Ni(NH 3 ) 6 ](NO 3 ) 2 complex crystals at 650 K. The Ni 3 N phase crystallizes in the hexagonal structure with unit cell parameters a ¼ 4.624(4) A and c ¼ 4.316(4) A, and has a crystallite size of 16 nm. In TEM study, these nanosize particles show spherical shape, and form particle aggregates of 18 nm size. Ni 3 N particles exhibit a Curie temperature of T C ¼ 634 K. In the field dependence magnetic measurements, the presence of hysteresis loop indicates ferromagnetic behavior with s s ¼ 1.678 emu/g, s R ¼ 0.50 emu/g and m 0 H c ¼ 0.022 T. In this phase, the density of states (DOS) of Ni is dominated by 3d states and is mixed with 2p DOS of N. The contribution of d-electrons in the intra-band polarization affects the magnetic moment of Ni and thus the magnetic moment of Ni 3 N.
IntroductionThe transition metal nitrides are very important for technological applications as well as fundamental studies because of their unusual combination of physical properties such as very high melting point, extreme hardness and metallic conductivity [1]. Interestingly, transition metal nitrides in the nanostructured form are most attractive for magnetic storage devices, catalytic studies, sensors, fuel cells, superconducting applications [2,3]. However the paucity of literature on metal nitrides illustrates that the much greater challenges are both in synthesizing and characterizing them with respect to their composition, structure and physical properties. The metastable Ni 3 N phase is reported as nanocomposite films of Ni 3 N/AlN along with the presence of elemental nickel [4]. In this paper, we present the synthesis of nanocrystalline nickel nitride (Ni 3 N) particles. These particles are obtained in the temperature range 613 to 673 K in NH 3 atmosphere from the nickel hexaamine nitrate complex where M-N linkage is present. Nanocrystalline Ni 3 N particles are characterized and studied for their interesting magnetic properties.
Nanocrystals having single-band red emission under near-infrared (NIR) excitation through the upconversion process offer great advantages in terms of enhanced cellular imaging in in vitro and in vivo experiments in the biological window (600−900 nm), as a security ink, in photothermal therapy (PTT), in photodynamic therapy (PDT), and so forth but are challenging for materials scientists. In this work, we report for the first time the preparation of a super bright red emitter at 655 nm from monodispersed NaErF 4 :0.5%Tm@ NaYF 4 :20%Yb nanocrystals (core@active shell). This phosphor exhibits 35 times stronger photoluminescence as compared to NaErF 4 :0.5%Tm@NaYF 4 (core@inactive shell). Here, an Er 3+ -enriched host matrix works simultaneously as an activator and a sensitizer under NIR excitation. Upconversion red emission at 655 nm arises due to the electronic transition of Er 3+ via the involvement of a three-photon absorption (expected to be a two-photon absorption), which has been confirmed via a power-dependent luminescence study. Tm 3+ ions incorporated into the core with the active shell act as trapping centers, which promote the red band emission via the back-energy transfer process. Moreover, the active shell containing Yb 3+ ions efficiently transfers the energy to the Er 3+ -enriched core, which suppresses the nonradiative channel rate, and Tm 3+ ions act as trapping centers, which reduce the luminescence quenching via reduction of energy migration to the surface of the host lattice. Also, we have shown the potential applications of these nanocrystals: cellular imaging through downconversion and upconversion processes and security ink.
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