Ce(III) ve Eu(III) katkılı YAG (Y3Al5O12) ve Zno seramiklerinin sentezi

This thesis consists of two parts. The first part of the thesis is dedicated to synthesis of Yttrium aluminum garnet (YAG) transparent ceramics and the second part is dedicated to the Cerium doped ZnO and Zn(OH)2 layered nanocomposites. Yttrium aluminum garnet (Y3Al5O12) has very good optical properties and chemical stability. When doped with rare earth ions, YAG is an excellent material for solid-state laser and phosphorus applications. In conventional solid-state laser applications glass or Czochralski grown single crystals are used as the gain medium. Though Czochralski grown single crystals are better than the glasses in terms of optical properties, the process of single crystal growth is time consuming and expensive. Polycrystalline YAG ceramics are alternatives to the single crystal grown materials and promising candidates for solid-state laser hosts. However, even twenty years after they were first reported as an efficient laser host, polycrystalline YAG ceramics are limited in laser applications. In recent years, ZnO materials have been in the center of interest because of their large band gap and large value of exciton binding energy. More importantly optical and electronic properties of ZnO materials can be changed by changing the morphology. Many different morphologies are well known for ZnO including, wires, tubes, rods, flowers, sheets, stars, belts. One such morphology is layered structure which forms with the aid of anionic surfactants. Layered metal hydroxides have structure based on naturally occurring material brucite (Mg(OH)2). In the first part of the thesis (Chapter I and II), various synthesis methods were used to produce Ce3+ and Eu3+ doped polycrystalline YAG samples to investigate their effect on powder characteristics. 1, 5 and 10% doped samples were prepared by hydrothermal, citrate, solid-state and co-precipitation methods. Both normal-strike and reverse-strike routes of co-precipitation method were conducted. TGA/DTA analysis showed that the samples were crystallized after 900˚C. Therefore, produced samples were calcined at different temperatures ranging from 900˚C to 1300˚C. XRD patterns of the samples showed that pure YAG phase was able to be achieved via reverse-strike route and citrate method at 900˚C while it was not possible with other methods at 900˚C. Intermediate phases YAM and iv YAP were not observed in reverse-strike or citrate methods. Also the effects of single and multiple step calcinations were investigated. YAG precursors were calcined at 900˚C and 1200˚C for several times. FESEM images showed that calcination temperature had little effect on grain growth on amorphous samples as long as the temperature is higher than the crystallization threshold. However, temperature increase enhanced the grain growth when samples were crystallized by a pre-calcination step. Pure YAG powders were doped with 0.28 wt% SiO2 and slip casted for shaping. After 8h of sintering at 1750˚C under 10-5 Torr vacuum, 50% transparency in the visible region was achieved. In the second part of the thesis (CHAPTER III), SDS intercalated Zn(OH)2 layered materials synthesized by hydrothermal method using HMT at 90˚C. Different HMT amounts were tried ranging between 0.002 mol and 0.012 mol per 0.002 mol starting salt, Zn(NO3)3. Samples without SDS were also produced to investigate the effects of the surfactant. The samples contained 1, 5 and 10% Ce3+ ion. FESEM results showed that samples were formed into nanosheet morphology with the addition of SDS. With the increasing reaction time sheets rolled up into a conic morphology. Samples contained no SDS yielded hexagonal rod-like morphology which is well documented in the literature. XRD results showed that samples can be crystallized into ZnO at 90˚C without the addition of SDS. However, this was not possible with the samples with SDS as all intercalated samples were in hydroxide form. With the increasing HMT amount the samples showed a significant particle growth.