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XRD patterns of undoped and doped Si3N4 nanowires. The two right figures show the enlarged XRD patterns around the main peaks
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In this work, Y-, Ce- and Tb-doped Si3N4 nanowires have been successfully synthesized by directly nitriding doped nanocrystalline silicon powders obtained by cryomilling. The obtained single-crystalline α-Si3N4 nanowires are nearly 20-50 nm in diameter and up to several micrometers in length. The photoluminescence properties of doped Si3N4 nanowire...
Citations
... 15 Moreover, Si 3 N 4 nanowires and nanoribbons have also been synthesized, which exhibit super ductility and extraordinary optical properties. 4,13,[16][17][18] In addition, ear-like Si 3 N 4 dendrites can be formed by the reaction of SiO 2 /Fe composites and Si powders in N 2 atmosphere. 19 Nevertheless, most of the above fabrication methods are high energy-or time-consuming, and it is still a challenge to achieve the fabrication of high-quality Si 3 N 4 with different morphologies by the control of fabrication conditions. ...
Silicon nitride (Si3N4) has great potential for applications in photoelectric and semiconductor fields. In this study, a novel strategy of fabricating Si3N4 crystals is reported, and the morphology of α-Si3N4 can be controlled. The aBN/SiO2/Si wafers were designed and irradiated by a high-energy electron beam for 2 min using home-made equipment. Tree-like α-Si3N4 dendrites and [001]-oriented unbranched α-Si3N4 whiskers can be synthesized by controlling the electron beam energy. Related formation mechanisms were analyzed based on componential and structural characterization using a scanning electron microscope and high-resolution transmission electron microscope. In addition, photoluminescence measurements indicate that the synthesized α-Si3N4 exhibit unique photoluminescence properties. This is attributed to α-Si3N4 forming abundant Si–Si bonds, Si dangling bonds, N dangling bonds and oxygen bonds in the synthesis process. These findings provide new insights into fabricating high-quality Si3N4 crystals, as well as developing related high-performance micro- or nano-devices.
... In most cases only Eu-and Tb-doped a-Si 3 N 4 thin lms and nanowires illustrating broad band emission are concerned. [33][34][35][36][37][38][39][40][41] Here we use the expression doping explicitly as this is given in the references. ...
... This indicated that if some luminescence spectra may seem very similar overall at rst sight, it turns out that denitely some changes are observed. [33][34][35][36][37][38][39][40][41] DFT calculations ...
Phosphor-converted white light emitting diodes (pc-LEDs) are efficient light sources for applications in lighting and electronic devices. Nitrides, with their wide-ranging applicability due to their intriguing structural diversity, and their auspicious chemical and physical properties, represent an essential component in industrial and materials applications. Here, we present the successful adsorption of Eu and Tb at the grain boundaries of bulk β-Si3N4 and β-Ge3N4 by a successful combustion synthesis. The adsorption of europium and terbium, and the synergic combination of both, resulted in intriguing luminescence properties of all compounds (red, green, orange and yellow). In particular, the fact that one host can deliver different colours renders Eu,Tb-β-M3N4 (M = Si, Ge) a prospective chief component for future light emitting diodes (LEDs). For the elucidation of the electronic properties and structure of β-Si3N4 and β-Ge3N4, Mott-Schottky (MS) measurements and density functional theory (DFT) computations were conducted for the bare and RE adsorbed samples.
... Early, Li et al. have prepared Eu 2+ , Ce 3+ and Tb 3+ doped ɑ-Si 3 N 4 by a solid-state method using a mixture of Si(NH) 2 and RE compounds in a N 2 /H 2 atmosphere, and studied their photoluminescence (PL) properties [17]. Lately, Huang et al. have synthesized Y, Ce and Tb doped Si 3 N 4 nanowires using directly nitridingdoped nanocrystalline silicon powders obtained by cryomilling [18]. However, the above-mentioned synthetic routes for RE doped Si 3 N 4 usually require complex procedures and long-term high-temperature conditions. ...
... However, Eu 3+ doped Si 3 N 4 nanowires show pure α-Si 3 N 4 phase from the XRD pattern, because they were collected at the cathode, away from the arc area, and the synthesis temperature is relatively low. Besides, as show in the enlarged XRD patterns ( Fig. 1(b)), the peaks in doped Si 3 N 4 nanowires are slightly shifted toward the lower angles compared with undoped Si 3 N 4 , implying that doping with larger RE ions leads to Si 3 N 4 lattice expansion, which is consistent with previous report [18]. However, due to the large size mismatch, the incorporation of RE ions into Si 3 N 4 is difficult. ...
... In the PL emission spectrum, the broad emission band ranges from 400 to 750 nm, centered around 500 nm, which is caused by the 5d-4 f transition on Ce 3+ . In previous reports, both Si 3 N 4 :Ce 3+ powders and nanowires showed emission bands of 450 nm [17,18]. Here, the emission peak centered at 500 nm is significantly red-shifted compared with other Si 3 N 4 :Ce 3+ . ...
Si3N4 nanowires doped with rare earth ions (such as Ce³⁺, Tb³⁺, Eu²⁺ and Eu³⁺) were synthesized by plasma assisted direct nitridation method using Si, rare earth oxides and N2 as raw materials. The prepared doped Si3N4 nanowires were characterized by XRD, EDS, XPS, SEM and TEM. The obtained single-crystal doped Si3N4 nanowires have uniform diameters of about 50-100 nm and lengths of more than 10 μm. The photoluminescence (PL), PL decay curves as well as thermal quenching behaviors of doped Si3N3 nanowires were systematically investigated. This work provides an effective strategy for doping large-size functional atoms in Si3N4 nanowires.
... These emission peaks could be caused by point defects [103]. As the energy was higher than the bandgap, sub-band emission could be observed excited at 400-450 nm as shown in Fig. 15 [106]. Fig. 17 exhibits the PL spectrum of undoped and doped Si 3 N 4 nanowires, which demonstrated that the PL performance of nanowires with different dopants were discrepant. ...
... Each doped Si 3 N 4 nanowires exhibited a dominating emission peak which was clearly stronger compared with undoped Si 3 N 4 nanowire, apart from that of Al. The discrepant effects of different dopants on the PL properties could be attributed to the disparate valence electronic structure of dopants [106]. ...
... The PL spectrum of Si 3 N 4 nanowires without and with various dopants[106]. ...
With advances in nanotechnology, nanowires have gained worldwide attention because of their novel properties and promising applications. Among them, silicon nitride (Si3N4) nanowires have attracted increasing attention due to their excellent performance and huge application potential. In this review, various synthesis methods of Si3N4 nanowires are introduced in detail, and then the growth mechanisms are also stated. Subsequently, the novel properties of Si3N4 nanowires including mechanical, optical, electrical, thermal, and wetting performance are highlighted. Applications corresponding to performance are also summarized later, such as composites, field emitters, field-effect transistors (FETs), photodetectors, photocatalysts, and microwave absorbers. Finally, the contents of this article are concluded and outlooks of future research directions are stated. This article reviews the recent advances and provides the prospects and challenges of Si3N4 nanowires.
... As a matter of fact, this kind of transition was suggested as the excitation mechanism of Tb 3+ and Ce 3+ ions in crystalline α-Si 3 N 4 powders [37]. From this point of view, the large broadening of B3 could be due to electron-phonon coupling which is usually very strong for f-d transitions [38][39][40]. ...
In this work, silicon nitride films containing terbium were deposited by reactive magnetron co-sputtering in a nitrogen enriched plasma and subjected to rapid thermal annealing treatments. The influence of annealing temperature on the emission and absorption properties of these films was investigated by photoluminescence, photoluminescence decay and photoluminescence excitation measurements. An increase in the photoluminescence intensity and photoluminescence decay time was observed upon annealing for the main ⁵ D 4 - ⁷ F 5 transition of Tb ³⁺ ions. This observation was attributed to decrease of the non-radiative recombination and increase of the number of excited Tb ³⁺ ions upon annealing. Moreover, high temperature annealing was found to shift the spectral position of absorption bands observed in the photoluminescence excitation spectra. In general, these excitation spectra were shown to have a rather complicated structure and were decomposed into three Gaussian bands. It was suggested that two of these excitation bands might be due to indirect excitation of Tb ³⁺ ions via defects and the third excitation band could be due to direct 4f-5d transition.
... Our next group of papers deals with mechanochemical effects in the synthesis, structure and properties of a wide variety of inorganic systems including metal alloys [8][9][10][11][12][13][14], oxides [15][16][17][18] and composites [19][20][21]; these studies include for example using cryomilling (milling attrition of powders with a cryogenic medium) to obtain nanocrystalline highentropy alloys [8], a shaker mill to produce nonequilibrium alloys in immiscible systems at room temperature [9], obtaining nanoparticulated LiFeM 2-O 6 (M = Ge, Ti) pyroxenes [18] and assessing the reactivity of highly exothermic metal oxide thermitetype composites subjected to mechanical activation [20], to mention some. Another group of papers studies the synthesis and properties of lanthanidedoped silicon nitride nanowires [22], Ti and Hf carbides [23], Ni boride [24], Zr boride ceramics [25] and Cu-and Sn-based sulfides [26,27]. Some of these systems are highly exothermic, and mechanically induced chemical reactions are real fast, achieving total conversion to products within minutes. ...
Based on first-principles calculations, we have studied the structural, electronic and optical properties of Be, Ca, Ba, and Eu doped β-Si3N4 systems. Firstly, after performing the structure optimization of the doped systems, the stability of the doped systems is verified via the calculation of the formation energy. Then, the electronic properties of the doped systems are studied based on the band structure and density of states. Compared with pure β-Si3N4, the bandgap of the doped systems becomes narrowed. Particularly the bandgap of the Eu-doped system is reduced to 0.209 eV due to the Eu 4f orbital, which broadens the development prospects of the application of Si3N4 materials in the semiconductor field. Meanwhile, the dielectric function, absorption and reflection coefficient are discussed to evaluate the optical properties of the doped systems. Finally, the verified experiment was carried out by a spark plasma sintering, according to the simulational results that the Eu doped system shows the potential for visible light absorption. The research provides both the theoretical and experimental bases for the preparation of color Si3N4 ceramics.
We used density functional theory (DFT) calculations to study the influence of alkali earth metal element (AE) doping on the crystal structure and electronic band structure of α-Si3N4. The diversity of atomic radii of alkaline earth metal elements results in structural expansion when they were doped into the α-Si3N4 lattice. Formation energies of the doped structures indicate that dopants prefer to occupy the interstitial site under the nitrogen-deficient environment, while substitute Si under the nitrogen-rich environment, which provides a guide to synthesizing α-Si3N4 with different doping types by controlling nitrogen conditions. For electronic structures, energy levels of the dopants appear in the bottom of the conduction band or the top of the valence band or the forbidden band, which reduces the bandgap of α-Si3N4.
