Structure refinement of yttrium ?-sialon from X-ray powder profile data

Electronic structure, thermodynamic stability and high-temperature sensing properties of Er-α-SiAlON ceramics

α-SiAlON ceramics have been in use as engineering ceramics in the most arduous industrial environments such as molten metal handling, cutting tools, gas turbine engines, extrusion molds, thermocouple sheaths, protective cover for high-temperature sensors, etc., owing to their outstanding mechanical, thermal and chemical stability. Taking advantage of the intrinsic properties of α-SiAlONs, we investigate, in this paper, the possibility of using the Er-doped α-SiAlON (Er-α-SiAlON) ceramic as a high-temperature sensing material via its unique near-infrared to visible upconversion property. We first use neutron diffraction and density functional theory calculations to study the electronic structure and thermodynamic stability of Er-α-SiAlON. It is found that the interstitial doping of Er stabilizes the α-SiAlON structure via chemical bonds with O-atoms with N:O ratio of 5:2 in the seven-fold coordination sites of the Er3+ ion. Temperature-dependent upconversion emissions are then studied under 980 and 793 nm excitations over a temperature range of 298-1373 K and the fluorescence intensity ratio (FIR) technique has been employed to investigate the temperature sensing behavior. Temperature-dependent Raman behavior is also investigated. We demonstrate that using Er-α-SiAlON as a sensing material, the limit of temperature measurement via the FIR technique can be pushed well beyond 1200 K.

Co-doping effect of Mn2+ on fluorescence thermostability of Ca-α-sialon:Eu2+ phosphors

To reveal Mn²⁺ influence on emission of Ca-α-sialon:Eu²⁺, the Mn²⁺ and Eu²⁺ co-doped phosphors were synthesized by a solid state reaction method. The produced powders show an enhanced fluorescence thermostability and the roles of Mn²⁺ addition have been investigated.

Parameters Affecting Pressureless Sintering of α'-Sialons with Lanthanide Modifying Cations

μ-silicon nitride forms a range of solid solution Mx(Si,Al)12(0,N)16 where x = 2 and M is Li+, Ca2+, y3+ or certain lanthanide cations. This paper reports the formation of Ln-α'-sialons by the reaction of Si3N4 with AIN and Ln2O3 where Ln=Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. Transformation reactions of Nd, Sm, Gd, Ho, Er and Y cations occurring during liquid phase pressureless sintering are reported. The effects of the volume and viscosity of the liquid phase and the amountof secondary N-melilite on sintering are discussed.

Crystal structure of NdSi(6-z)Al(1+z)O(z)N(10-z) (z = 0.4) determined by single-crystal X-ray diffraction

Single crystals of JEM-phase NdSi(6-z)Al(1+z)O(z)N(10-z) were successfully prepared from starting powders of Si₃N₄, AlN and Nd₂O₃ at 1700 °C for 3 h under nitrogen atmosphere. The z value of Nd-doped JEM-phase was determined to be 0.4 via determination of oxygen and nitrogen by elemental analysis. This result may be beneficial for overcoming the difficulty on preparation of single-phase JEM-phase Sialon materials and further characterization on their properties. The detailed crystal structure of Nd-Sialon was solved on the basis of single-crystal X-ray diffraction data for the first time. The space group is Pbcn (no. 60); a = 9.3060(6) Å, b = 9.7224(6) Å, c = 8.8777(5) Å; Z = 4; V = 803.22(8) ų; D(c) = 3.971 g cm⁻³; R₁ = 0.0297 and wR₂ = 0.0739 for all reflections refined against F², with GooF value of 1.031.

Strong Green Emission from α-SiAlON Activated by Divalent Ytterbium under Blue Light Irradiation

This contribution reports on luminescence properties of divalent ytterbium in alpha-SiAlON at room temperature. Ytterbium-doped alpha-SiAlON powders, with the compositions of (M(1-2x/v)Yb(x))(m/v)Si(12-m-n)Al(m+n)O(n)N(16-n) (M = Ca, Li, Mg, and Y, v is the valency of M, 0.002 < or = x < or = 0.10, 0.5 < or = m = 2n < or = 3.5), were synthesized by sintering at 1700 degrees C for 2 h under 0.5 MPa N2. A single, intense, broad emission band, centered at 549 nm, is observed due to the electronic transitions from the excited state 4f(13)5d to the ground state 4f14 of Yb2+. The luminescence of Yb2+ in alpha-SiAlON occurs at relatively low energy, which is attributable to the large crystal field splitting and nephelauxetic effect due to the nitrogen-rich coordination of Yb2+. The dependence of luminescence properties on the Yb2+ concentration, chemical composition, and annealing is discussed. It is suggested that this novel green phosphor could be applied in white light-emitting diodes (LEDs) when combined with a red phosphor and a blue LED.