Method for obtaining sodium tungstate-bismuth crystals

FIELD: metallurgy.

SUBSTANCE: invention refers to growth from molten metal of non-alloyed crystals of sodium tungstate-bismuth NaBi(WO4)2 being perspective material for Cherenkov detectors. Growth of crystals is performed using Chokhralsky method in air atmosphere at drawing speed of 4-5 mm/hour and crystal growth speed of 15-19 min-1.

EFFECT: method allows obtaining crystals transparent in visible range beginning from wave length of 352 nm.

3 dwg, 4 ex

 

The invention relates to the field of crystal growth from the melt. The tungstate of sodium bismuth NaBi(WO4)2promising material for Cherenkov detectors.

A method of obtaining crystals of NaBi(WO4)2by the Czochralski method [E.G.Devitsin, V.A.Kozlov, V.A.Nefedov, A.R.Terkulov, B.I.Zadneprovski. Colorless NaBi(WO4)2: In Cherenkov Crystals for Electromagnetic Calorimetry. Scientific information journal "ALLY", 2003, vol. 5, No. 28, p.1-14] - prototype, in which the crystals are grown in air from platinum crucibles, with a speed of extrusion of 4-5 mm/h at a speed of 30-32 min-1. According to this method, the obtained undoped crystals of NaBi(WO4)2and crystals, doped indium.

The main disadvantage of the prototype method is that non-alloy crystals of NaBi(WO4)2almost opaque in the wavelength range 352-380 nm, which reduces the effectiveness of their use in Cherenkov detectors. When growing crystals by the method prototype, to ensure transparency in the specified range, NaBi(WO4)2you must legitamate indium, which complicates the process.

Figure 1 presents the authors ' method-prototype [E.G.Devitsin, V.A.Kozlov, V.A.Nefedov, A.R.Terkulov, B.I.Zadneprovski. Colorless NaBi(WO4)2: In Cherenkov Crystals for Electromagnetic Calorimetry. Scientific information journal "ALLY", 2003, vol. 5, No. 28, C.-14] spectra of transmittance unalloyed NaBi(WO 4)2and crystal doped with indium. From the spectra in figure 1 shows that the undoped crystal NaBi(WO4)2transparent in the visible range since the wavelength of 380 nm and doped with indium - since the wavelength of 352 nm.

The objective of the invention is to simplify the process of obtaining crystals of NaBi(WO4)2transparent in the wavelength range 352-380 nm.

This problem is solved in the proposed method in air atmosphere from a platinum crucible with a speed drawing of 4-5 mm/hour by growing undoped crystals of NaBi(WO4)2speed 15-19 min-1.

Figure 2 shows the crystal NaBi(WO4)2grown for the proposed method (left), and preparation of the solid Cerenkov detector of such a crystal (right).

Figure 3 presents the spectrum of transmittance of the crystal NaBi(WO4)2grown on the proposed method. It is seen that the material is transparent in the visible range since the wave number 28400 cm-1that corresponds to a wavelength of 352 nm.

Thus, the obtained undoped NaBi(WO4)2transparent in the wavelength range 352-380 nm.

The achieved result can be explained as follows. When growing NaBi(WO4)2high speed extrusion and rotation in Cree is the tall, as correctly noted by the authors of the prototype method, the formation of point defects, namely vacancies tungsten and bismuth atoms, occupying the place of the sodium atoms in the lattice (see [E.G.Devitsin, V.A.Kozlov, V.A.Nefedov, A.R.Terkulov, B.I.Zadneprovski. Colorless NaBi(WO4)2: In Cherenkov Crystals for Electromagnetic Calorimetry. Scientific information journal "ALLY", 2003, vol. 5, No. 28, p.4]). These defects cause the appearance of deep energy levels in the forbidden zone NaBi(WO4)2causing intense light absorption in the wavelength range of 350-420 nm and, as a result, the opacity of the crystals in the wavelength range 352-380 nm. In the method prototype transparency of the crystals in the wavelength range 352-380 nm is achieved by compensation of deep levels with the introduction of impurities India. In the proposed method, by reducing the speed of rotation of the crystal, significantly reduced the concentration of point defects in NaBi(WO4)2that allows you to get undoped crystals, transparent in the wavelength range 352-380 nm. The exception alloying simplifies the process.

The proposed interval speed selected experimentally. At speeds above 19 min-1significantly increases the concentration of point defects in crystals, and, as a consequence, NaBi(WO4)2intensively absorbs light with wavelengths 352-380 nm. When the rotation speed is s below 15 min -1growing quality NaBi(WO4)2impossible, as in this case, the growth mechanism is replaced by the dendritic and the crystals formed many structural macro defects, which makes it impossible to use NaBi(WO4)2in Cherenkov detectors.

Example 1

Crystal tungstate of sodium-bismuth NaBi(WO4)2grown by the Czochralski method in air atmosphere from a platinum crucible with a speed drawing of 4 mm/hour and the speed of rotation of the crystal 14 min-1. To get a quality NaBi(WO4)2fails due to dendritic growth mechanism of the crystal.

Example 2

Crystal tungstate of sodium-bismuth NaBi(WO4)2grown by the Czochralski method in air atmosphere from a platinum crucible with a speed drawing 5 mm/h and the speed of rotation of the crystal 15 min-1. The obtained crystal NaBi(WO4)2transparent in the wavelength range 352-380 nm.

Example 3

Crystal tungstate of sodium-bismuth NaBi(WO4)2grown by the Czochralski method in air atmosphere from a platinum crucible with a speed drawing of 4 mm/hour and the speed of rotation of the crystal 19 min-1. The obtained crystal NaBi(WO4)2transparent in the wavelength range 352-380 nm.

Example 4

Crystal tungstate of sodium-bismuth NaBi(WO4)2expression is foreseen by the Czochralski method in air atmosphere from a platinum crucible with a speed drawing 5 mm/h and the speed of rotation of the crystal 20 min -1. The obtained crystal NaBi(WO4)2almost completely absorbing light in the wavelength range 352-380 nm, i.e. non-transparent in this range.

The method of producing crystals of sodium tungstate-bismuth NaBi(WO4)2by the Czochralski method in air atmosphere from a platinum crucible with a speed drawing of 4-5 mm/h, characterized in that the speed of rotation of the crystal is 15-19 min-1.



 

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