Bridgman-stockbarger yöntemi ile CsCdBr3 tek kristalinin büyütülmesi ve optik özelliklerinin incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 75168
- Danışmanlar: DOÇ. DR. GÖNÜL ÖZEN
- Tez Türü: Yüksek Lisans
- Konular: Fizik ve Fizik Mühendisliği, Physics and Physics Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Fizik Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 115
Özet
ÖZET Bu çalışmada CsCdBr3 tek kristalinin Bridgman-Stockbarger tekniği kullanılarak büyütülmesi amaçlanmıştır. Tek kristal büyütme işleminden önce bir ön sentez sistemi tasarlanarak kurulmuştur. Sistemde kullanılan bir bölgeli ön sentez fırını ayrıca tasarlanarak yapılmıştır. Malzeme bu sistem yardımı ile poli-kristal olarak sentezlenmiştir. Daha sonra bu malzemenin tek kristal olarak büyütme işleminde kullanılan üç bölgeli Bridgman-Stockbarger sisteminin kullanılması için CsCdBr3 tek kristalinin ergime sıcaklığı dikkate alınarak gerekli sıcaklık ve çekme hızı parametrelerinin optimizasyonu yapılmıştır. Büyütme işlemi için gerekli lineer sıcaklık gradyenti elde edilmiş ve malzeme tek kristal olarak büyütülmüştür. Elde edilen kristalin X-ışını difraktometre analizi yapılmıştır. IX
Özet (Çeviri)
SUMMARY GROWTH OF CsCdBr3 SINGLE CRYSTAL BY BRTOGMAN-STOCKBARGER TECHNIQUE AND INVESTIGATION OF ITS OPTICAL PROPERTIES The aim of this work was the growth of CsCdBr3 single crystal using Bridgman-Stockbarger technique. This technique is known to give single crystals with a good quality if they have melting temperatures below 1200 °C. Growth and characterization of numerous new compounds to be used in compact visible-light sources have received considerable attention, recently for their anticipated uses in optical displays, data storage, cytology, and various spectroscopic and sensing applications. Blue sources are of special interest in optical memories because the storage density on an optically written disk varies as the inverse square of the wavelength. For example, one could anticipate an increase of as much as fourfold in the data stored by writing at short visible wavelenghts, rather than in the near infrared, as at present. Recently, there has been great interest in the study of materials capable of converting infrared light into shorter wavelengths by means of successive multi- photon absorptions and/or energy transfers. This process, called frequency up- conversion, is of practical interest because it provides an alternative method to intracavity frequency doubling for blue generation from infrared laser diodes, requiring a precise control of the temperature of the device. Energy transfer between ions in dimers or larger aggregates can be very efficient in rare-earth-doped compounds. CsCdBr3 which belongs to the AMX3 family has the hexagonal structure of CsNiCİ3. This crystal is very interesting matrix for such studies because trivalent impurities enter this host neraly only as charge compensated complexes. CsCdBr3 has infinite linear chains of face sharing (cd2+Br6J octahedra along the crystallographic c axis. Cd2+ ions are located in sites of trigonal D3d point group symmetry, while the Cs“ ions are located between the chains. As the distance between Cd+2 ions along a chain is much less than the seperation between chains, the structure is essentially one dimensional. as can be seen in Fig. 1 and Fig 2. Before growth of the CsCdBr3 single crystal, it has to be presynthesised in a presynthesis system, given in picture 1. The vacuum system and the presynthesis furnace which are two important parts of this sysytem were designed and built up.The presyntesis furnace is a single zone resistance furnace and its working temperature up to 1200 °C which about two times higher than melting point of CsCdBr3. The techical parameters of the furnace are as given below: Maximum Power =1500 watt Maximum Current = 8 A Input Voltage = 220 V Resistance = 22Q Furnace ceramic consists of 0% Fe and high grade, Al. It has the size ofLenght: 40 cm an Internal diameter: 3.8 cm and External diameter: 5 cm Kanthal DSD having the parameters given below was used as the resistance wire : Q=1.07 P=1.577W/cm2 d=1.2mm 1 = Wire lenght= 20256 mm The lenght of the wire necessary in order to heat up to 1200 °C was calculated using the formula: 1= KU2d2 4 pP where U: nominal voltage; d: diameter of the wire; p: resistivity; P,: surface power The wire was wounded regularly around of the ceramic. The vacuum system consists of the LEYBOLD AG turbomoleculer pump and a vacuum tub. The tub was designed for up to 10”5 mbar vacuum condition and made at Istanbul University Glass Atellier. After preparetion of the presyntesis system, CsBr and CdBr2 ( %99.999, Aldrich) was prepared according to a stoichiometric mixture of each filled into Bridgman crucible cleaned with special solutions. Crucible size and molar fraction of the materials are as given below: Crucible used: External diameter = 8 mm Internal diameter = 6 mm Lenght =15 mm Materials used: CsBr= 1.064 gr/mol CdBr2= 1.361 gr/mol For the presynthesis of CsCdBr3, the crucible was placed on the system and, then the system was turned on. The mixture of CsBr and CdBr2 in the crucible was dried at 300 °C first under vacuum for 4 hours and latter under Hbr gas for 2 hours. Fallowing the temperature of the furnace was raised above the melting temperature to melt the CsBr + CdBr2 mixture. XIAfter the crucible was seald with the aid of a source of O2, the melt was left to cool down to room temperature slowly. As a result of these processes polycrystaline of CsCdBr3 was prepared according to the formula of chemical reaction is : CsBr + CdBr2 Heat > CsCdBr:, + H2 / Polycristaline material in the sealed Bridgman tube was placed into three zone Bridgman system provided from CRYSTALOX (Picture 2) and lowered along a linear temperature gradient of 5°C / 1 cm in the middle of the furnace. This was repeated for different speeds of lowering between 1.5-1 mm/hour. The material obtained from this growth process was analysised by using x-ray difraction method. Also a quantitative analyis method must be used to find out detailed structure of the material. xiiFig 1 (Cd2+Br*- linear chainsFig 2 Structure of CsCdBr3 xivPicture 2 Three zone Bridgman system xv
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