Activation of Lead Fluoride Room Temperature Luminescence by Structural Modifications
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that the external
treatments - plastical
deformation,
ning and annealing, increasing the concentration of enhance the luminescence intensity.
thermal harde-
the intrinsic defects,
EXPERIMENTAL TECHNIQUE The experiments were held on lead fluoride cubic and orthorombic crystals, which preparation is described in the previous work. The studies of Xray- and photoluminescence spectra applied the methods described in the same paper [1]. To get the information about the volume atomic structure of the samples Raman scattering spectra were studied in the normal to the exciting light direction. The deformation of the samples was held at the testing "Instron" machines, equipped with high temperature accessories. The influence of gamma-irradiation on the photoluminescence of the C lead fluoride and its radiation hardness have been studied as well. Co-60 isotope was applied as gamma-source.
The irradiation dose varied from 10 3to the third
up to 3x108 rad . Experimental results and discussion It's known that at the room temperature the orthorombic modification of lead fluoride is stable. But the large magnitude of the volume effect of the 259 Mat. Res. Soc. Symp. Proc. Vol. 348. 01994 Materials Research Society
•
f%
I.u
1.0
-"
T =77K
.
to 0.5
T
=
77K
0.5
Orthorombic
>4,
C: C 0.0
-
CubicC
C 0.0
50 i001502002501300350400 CJ(cm)
Fig.1 Raman scattering spectra of orthorombic lead fluorid.
50100 15020025 0300350400 6 (CMe)
Fig.2. Raman scattering spectra of cubic lead fluorid .
transformation C-O (about 8%) induces large mechanical stresses, which hinder the transformation development in a volume sample. Due to this circumstance in some cases the C-phase can appear only at the sample surface. So the structural state of the samples was determined in this study by the two techniques: X-ray structural analysis and Raman light scattering. X-ray diffractometry can determine the crystalline structure in the layer adjacent to the surface with the thickness of about several microns. The Raman light scattering technique in the geometry used in this work gives the information about the crystal volume, because for the scattering excitation we applied the lasers with the photons energy much less than the forbidden gap of the crystal, which excite the Raman scattering in the whole volume of the sample (helium cadmium laser with the wavelength 441.6 nm and argon laser with the wavelength 488 nm). The Raman scattering spectrum of the orthorombic (0) lead fluoride is presented at Fig. l. It's worth noting that in the Raman spectra of 0 lead fluoride samples, produced by different means, identical lines are observed. The Raman spectrum of C lead fluoride (Fig.2) differs essentially from the spectra of O-crystal and coincides with the described elsewhere [2]. The studies of the surface and volume structures of lead fluoride have shown that the thin layer of O-phase appeared at the surface of the C lead fluoride after the mechanical surface processing. The homogeneous and transparent (the gap equals 5.17 ev) orthorombic
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