In this study, changes in the amount of potassium chloride liquid phase used for the molten‐salt synthesis of strontium ferrite were examined to understand the transition of the growth mechanism with temperature. The results of this investigation indicate that an increase in reaction temperature from 900° to 1200°C caused the particle shapes to become nearly spherical. In addition, the particle size decreased as the relative amount of liquid increased. The growth process of the strontium ferrite particles in the molten salt appears to have undergone a transition from an interfacial, reaction‐controlled mechanism to a diffusion‐controlled mechanism as temperature is increased.
Ammonia gas was blown into the solution of zirconium ion to induce homogeneous precipitation of supersaturated zirconium ion at gas-liquid interface with increase in pH. The precipitates formed using interface of gas-liquid phase were decomposed into fine spherical zirconia powder of high purity. As Concentration increase, mean diameter of particles increases to 140, 180, 240, 290 and 630nm. At pH of 4.5, maximum yield of 98.7% was obtained. From the above pH of 4.5, yield has been kept constant. Above pH of 5.0, large aggregates of precipitate consisting of primary particles were formed, and this may have been caused due to the existence of isoelectric point. Below pH of 4.5, almost aggregate-free fine spherical powders with particle size of below 100nm were produced.
Eu 3þ -doped Y 2 O 3 red phosphor 'was prepared in order to study the relationship between variation of Eu 3þ content and an excitation source such as low and high voltage energy and a vacuum ultraviolet (147 nm). The luminescence properties of pigment-coated Y 2 O 3 :Eu by various coating methods and different energy sources were also investigated. Excitation under a vacuum ultraviolet (VUV) for the red phosphor with different amounts of Eu 3þ activator exhibited similar luminescence property with the case of being excited by electrons accelerated under low voltage conditions. The surface of Y 2 O 3 :Eu red phosphor was treated with -Fe 2 O 3 pigment by two different methods to improve color purity. One was the adsorption utilizing -Fe 2 O 3 submicron-particles on the phosphor and the other was a precipitation method utilizing Fe(NO 3 ) 3 -urea orhexamethylenetetramine (HMTA). The red phosphor treated with an increasing amount of -Fe 2 O 3 showed decreasing luminescent intensity, but the color purity improved. The luminescent properties of phosphor treated with -Fe 2 O 3 pigment by the adsorption method exhibited much less dependency on the applied energy source. Surface treatment by the precipitation method, however, resulted in much a faster decrease of luminescent intensity with a lowering of the applied voltage and VUV region because of a more homogeneous coating of -Fe 2 O 3 pigment on the phosphor.
To improve the luminescent efficiency of conventional (Y,Gd)BO 3 :Eu 3+ red-phosphor for the plasma display panel (PDP), we have developed a new synthetic method such that the stoichiometric amount of boric acid is reacted with small-sized and spherical (Y,Gd) 2 O 3 :Eu 3+ phosphor oxides prepared by thermal decomposition of urea. The sol-gel method using citric acid as a complex-networking and fuel agents was also applied to compare the difference in luminescent efficiency under the vacuum ultraviolet (VUV) excitation depending on the synthetic methods. In this study, the most efficient composition of orthoborate was determined to be (Y 0.64 Gd 0.31 )BO 3 :0.05Eu 3+ . Orthoborate phosphor materials prepared by this new synthetic method have exhibited more effective VUV absorption in the range from 140 nm to 180 nm, and thus higher emissive brightness under the PDP operating condition than those of commercial phosphor and materials prepared in sol-gel method. It is proposed that the present new synthetic method can improve crystalline purity and spherical morphology of phosphor particles and thereby the luminescent efficiency. IntroductionThe luminescence performance of phosphors in plasma display panel (PDP) is governed by the absorption of the vacuum ultraviolet (VUV) light as well as luminescent efficiency of material [1]. It has been recently reported that the penetration depth of VUV radiation for phosphor material is in the range of about ten nanometers [1,2]. This suggests small-sized phosphor materials to be more effective for PDP applications. In addition, high purity phosphor materials are required for the improvement of luminescent efficiency because the impurities or defects often act as the quenching sites. (Y,Gd)BO 3 :Eu 3+ used as a standard red phosphor material for full color PDP has the fundamental problem of poor color purity. Considerable effort has been devoted to search for alternative superior red phosphors. Unfortunately, there is no report on red phosphors which are more effectively available in PDP than (Y,Gd)BO 3 :Eu 3+ up to now. The typical solid state reaction makes it difficult to synthesize orthoborate phosphors of pure phase with proper particle size and morphology because of necessity of high reaction temperature, long heating time, and subsequent milling process as well as high volatility of boric acid [3,4]. It is well known that the hydroxide precipitation method using the thermal decomposition of urea in aqueous solution can be utilized in the synthesis of Y 2 O 3 :Eu 3+ with high crystallinity, controlled size, and spherical morphology at lower temperature compared to solid state method [5]. However, this method can not be used for the synthesis of (Y,Gd)BO 3 :Eu 3+ because boric acid is hardly precipitated in this alkaline aqueous solution. Therefore, we developed two-step synthetic method such that the hydroxide precursors prepared by coprecipitation method in various conditions are reacted with boric acid. The crystallinity, morphology, and VUV photoluminescent (PL) prope...
CaTiO3:Pr3+ as an oxide phosphor is expected to be applied for a field emission display(FED) due to its relatively high conductivity. For the practical use, however, the CL intensity of CaTiO3:Pr3+ has to be enhanced. We introduced Ga3+ as a co-activator into the phosphor and investigated the CL characteristics with various Ga3+ concentrations. The CL intensity of CaTiO3:Pr3+ was remarkably increased when Ti4+ atom was replaced by the Ga3+. When the Ga3+ concentration is 5 times of Pr3+ molar concentration, the emission intensity of the CaTiO3:Pr3+ phosphor with Ga3+ is about 5 times higher than Ga3+-free samples. So, it was concluded that the addition of Ga3+ is essential to enhance CL property at low voltage. We proposed the following mechanism that excitation into the host lattice leads to the formation of electrons in the conduction band and holes in the valence band. The electrons in the conduction band recombine with the holes trapped at Ga3+ and this energy is effectively transferred to Pr3+ ion, which gives its own characteristic red emission.
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