ZnS precipitation: morphology control

ZnS is the most important base material for cathode-ray tube luminescent materials. In order to meet the requirements of various types of luminescent screen, routes to ZnS powder with adjustable particle morphology were investigated. The most important morphological parameters of ZnS phosphors are the particle size and the particle size distribution. Industrially, ZnS synthesis is performed by precipitation in an aqueous medium. Precipitation methods included in this study are homogeneous precipitation, precipitation in liquid crystal phase and the introduction of seeds. The powders received were processed to luminescent materials in a standard manner. The results are discussed in relation to raw ZnS powder properties as well as to the morphology and performance of the resulting annealed phosphor powders. From the methods investigated, the use of seed sols based on nanosized CuS, ZnS and S particles yielded the best results, namely, well-defined phosphor particles of micron-scale diameter.     

Radiation pattern design of photonic crystal LED optimized by using multi-objective grey wolf optimizer

Photonic Network Communications - This paper proposes an effective method for shaping the radiation pattern intensity of photonic crystal (PhC) light-emitting diode (LED). In this method, the...     

Synthesis and characterization of rod-like Y2O3 and Y2O3:Eu3+

Y₂O₃ rods 100 to 200 nm in diameter and 10 to 20 m in length are accessible via polyol-mediated synthesis of a precursor material with similar shape. By heating of Y(CH₃COO)₃ · xH₂O and a defined amount of water at 190°C in diethylene glycol, the rod-like precursor material is formed. Infrared spectroscopy (IR), differential thermal analysis (DTA) and thermal gravimetry (TG) evidence that this precursor material still contains acetate. However, the precursor material can be transformed to Y₂O₃ by sintering at 600°C without destruction of the rod-like shape. According to X-ray powder diffraction analysis, the rods are well crystallized. They can be assumed to be with [100] orientation. By doping with Eu³⁺ (5 mol%), red emitting phosphor rods can be realized. With optical spectroscopy the typical line emission of Eu³⁺ is observed. Diffuse reflectance of Y₂O₃:Eu³⁺ rods is determined to be higher than 95% in the visible. While exciting at 254 nm (Hg-discharge), a quantum efficiency of 38.5% is proven for the prepared Y₂O₃:Eu³⁺ rods.     

Homogeneous coatings of nanosized Fe2O3 particles on Y2O2S:Eu

The red emitting phosphor Y₂O₂S:Eu commonly applied in colour television tubes was pigmented with a thin homogeneous layer of nanosized Fe₂O₃ particles based on a novel coating strategy. In a first step the phosphor was covered with nanosized Fe₃O₄ particles which themselves were prepared by reduction of an Fe(III)-salt with hydrazine. Thereafter, Fe₃O₄ was converted to Fe₂O₃ by heating to 450°C in air. Surface composition and body colour of the corresponding phosphor samples were investigated applying ESCA and measuring diffuse reflectance. The size of the Fe₂O₃ particles as well as the homogeneity of the resulting coating were studied by SEM. Furthermore, the adhesion of Fe₂O₃ particles on the phosphor surface was examined.