The zinc alkoxy(siloxy) complex {Zn[OSi(OtBu)3]2}2 has been prepared and studied as a molecular precursor to zinc orthosilicate, Zn2SiO4. This complex, prepared by reaction of ZnMe2 with HOSi(OtBu)3, has been characterized by X-ray crystallography as a dimer with two four-coordinate zinc centers. It cleanly looses isobutene, tert-butyl alcohol, and HOSi(OtBu)3 at ca. 100 °C to produce Zn2SiO4·SiO2. Reaction of ZnMe2 with (HO)2Si(OtBu)2 affords the hydrocarbon-soluble polymer [ZnOSi(OtBu)2O]n, which is proposed to have a structure consisting of four-coordinate Zn atoms linked by bridging −O(tBuO)Si(OtBu)O− groups. This polymer undergoes a very clean ceramic conversion over 150−250 °C to give the theoretical yield of carbon-free (by infrared spectroscopy and combustion analyses) Zn2SiO4·SiO2. The pyrolytic elimination products consist of water, tert-butyl alcohol, and isobutene. X-ray diffraction studies on the ceramic products show that Zn2SiO4 is the only zinc-containing, crystalline product formed. Thus ...

Molecular and polymer precursor routes to manganese-doped zinc orthosilicate phosphors

Manganese doped nanocrystalline willemite powder phosphors $Zn_{2-x}Mn_xSiO_4$ $(0.1 \leq x \leq 0.5)$ have been synthesized by a low-temperature initiated, self-propagating, gas producing solution combustion process. The phosphors have been characterized by using x-ray diffraction (XRD), energy dispersive spectroscopy, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR), and photo luminescence (PL) spectroscopic techniques. The lattice parameters calculated from XRD confirm that Zn2–xMnxSiO4 has a rhombohedral space group R3H. The XRD patterns confirm that $Zn_{2-x}Mn_xSiO_4$ phosphor samples undergo a phase transformation from \beta -willemite to \alpha -willemite phase at 950 °C. The EPR spectra of Mn2+ ions exhibit resonance signals at g \cong 3.24 and g \cong 2.02, with a sextet hyperfine structure centered around g \cong 2.02. The EPR signals of Mn2+ give a clear indication of the presence of two different Mn2+ sites. The magnitude of the hyperfine splitting (A) indicates that the Mn2+ is in an ionic environment. The number of spins participating in resonance (N), the paramagnetic susceptibility (\chi ), and the zero-field splitting parameter (D) have been evaluated as function of x. It is interesting to observe that the variation of N with temperature obeys Boltzmann. The paramagnetic susceptibility is calculated from the EPR data at various temperatures and the Curie constant and Curie paramagnetic temperature was evaluated from the 1/ \chi versus T graph. The luminescence of Mn2+ ion in Zn2SiO4 shows a strong green emission peak around 520 nm from the synthesized phosphor particles under UV excitation (251 nm). The luminescence is assigned to a transition from the upper 4T1 6A1 ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.

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Solution combustion derived nanocrystalline Zn(2)SiO(4):Mn phosphors: a spectroscopic view.

The phosphors of high luminous efficiency for plasma display panel (PDP) applications must have high purity, single phase, uniform particle size, and clean surfaces. Photoluminescence characteristics of europium-doped yttrium oxide phosphors of spherical shape as well as optimum synthetic conditions for maximal luminescence were investigated through emission spectroscopy, X-ray spectroscopy, and scanning electron microscopy. It was found that the spherical Y 2 O 3 :Eu phosphors had good mechanical properties and high emission spectra for device application Optical characteristics of spherical phosphors were mainly dependent on synthetic temperature, doped activator concentrations, particle size, and annealing process. Especially, it was observed that the europium distribution in the host lattice of our samples prepared by aerosol pyrolysis was quite different from that of commercial phosphors by the solid-state reaction method. The resultant spherical phosphors show comparable luminescent properties to the commercial product (product by Nichia Co.) This paper describes the synthetic technique and discusses physical and luminescent properties of spherical phosphors in comparison to the characteristics of phosphors prepared by the solid-state reaction method.

Photoluminescence Characteristics of Spherical Y 2 O 3 : Eu Phosphors by Aerosol Pyrolysis

The purpose of the present study is to develop an understanding of the photoluminescence properties of Mn2+-doped zinc silicate (Zn2SiO4:Mn) phosphors, which have served as a gree-emitting phosphor in many industrial applications. Thus, several experimental techniques, such as time-resolved emission spectra, decay curves, and time-resolved photoluminescence excitation spectra, have been conducted on Zn2SiO4:Mn phosphors. The characterization has been performed in terms of dopant concentration. The decay curves, together with the characteristic decay time, in particular, are measured as a function of excitation-light wavelength, in the range of 200–520 nm. The decay behavior is strongly dependent on the excitation-light wavelength. The excitation range is categorized into three regimes: the manganese direct excitation range, below the absorption-edge (ET) energy level; the manganese ionization range, from ET to the optical band-gap energy (Eg) of Zn2SiO4; and the intergap transition range, above the Eg energy level.

Photoluminescence Behavior of Manganese‐Doped Zinc Silicate Phosphors

Low-temperature synthesis of pure and Mn-doped willemite phosphor (Zn2SiO4:Mn) in aqueous medium

Zinc silicates are important in CRTs and lamp phosphors. Previous work has shown that a sol‐gel‐like method (termed CGUPS) can produce uniform zinc silicate phosphor particles whose surface layer possesses an appropriate activator concentration gradient and exhibits efficient cathodoluminescence (CL). This work further investigates this synthesis method in detail and verifies quantitatively the processing parameters for yielding optimal phosphors. Phosphors are evaluated as a function of starting silicic acid particle size ranges and activator (Mn) and coactivator (As) concentrations. Our results indicate that the CGUPS synthesis is not very sensitive to the processing parameters within their initially defined ranges. This study also demonstrates that the CL efficiency of phosphors does depend on particle size and is maximum for 4–7 and 7–12 μm size range with 10 keV electron excitation. For optimal CL efficiency and persistance, the Mn concentration is found to be 0.3% in terms of Mn/Zn ratio and the As/Mn ratio is 36%.

J. S. Wilson

Papers

Refinement of Zinc Silicate Phosphor Synthesis

Refinement of Zinc Silicate Phosphor Synthesis.