Comparative Studies of Optical Spectra in PbF 2 at Different Excitations
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gate the spectral characteristics. The Raman light scattering was studied with DFS-24 and MICRODIL-28 spectrometers. To investigate the X-ray luminescence we employed a W tube (30-50 kV, 32 ma). The luminescence of crystals was also studied with excitation by a-particles of 0.9 MeV at a current density of 2 ± 0.5 na. EXPERIMENTAL RESULTS AND DISCUSSIONS Table 1 summarizes the data on the emission of 0 and C lead fluoride for ac-particles excita-
tion. Table 1. The emission of 0 and C lead fluoride excited by a-particles Sample
Cubic Single Crystal
Pulse (number)
Compacted Cubic Polycrystal 248200
197300
Compacted Orthorhombic Polycrystal 937700
Figure 1 shows the emission spectra of the C- and 0-modifications of lead fluoride at 77 K. In these experiments we excited PL by the nitrogen laser with X=337.1 nm, here after PLN. It should be noted that the emission intensity of 0 lead fluoride at 77 K is 10-50 times higher than that of C lead fluoride. Their spectra are also different. We observe the emission maxima of 0 and C lead fluoride at X=500 and 460 nm with half-widths of 0.7 and 0.9 eV, respectively. The emission intensities for both lead fluoride modifications decrease as the temperature increases, as shown in Figure 2. However, if the intensity of the cubic modification decreases at 300 K by several orders with respect to the intensity at 77 K, then for 0 lead fluoride this drop is only several times. This fact allows us to investigate the spectral characteristics of 0 lead fluoride at
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Wavelength (nm) Figure 1: Emission spectra of lead fluoride excited by a nitrogen laser.
250 T,K
Figure 2: Temperature dependencies of photoluminescence of lead fluoride.
266
300 K. According to Figure 3, the 0 lead fluoride spectrum broadens somewhat as the temperature increases from 77 to 300 K, at which it becomes 0.8 eV wide. Unfortunately, we were unable to study the spectral characteristics of PL in C lead fluoride at 300 K because of the weak intensity. At the same time, the emission spectrum of C lead fluoride can be recorded for excitation by X-rays. As follows from Figure 4, the spectrum of X-ray luminescence (XL) of C lead fluoride has its maximum of X=490 nm and a halfwidth of 0.8 eV. The spectral characteristics of XL in 0 lead fluoride at 300 K is displaced to greater wavelengths as compared to PL of 0 lead fluoride (Figure 3). The XL maximum of 0 lead fluoride is observed at X=530 nm and the halfwidth of XL is 0.95 eV. The XL intensities (Ix) of the 0- and C-phases, as distinguished from PL, are similar at 300 K and comprises approximately 0.01 of the intensity of XL Bi 4 Ge 3O 12 (BGO). At the same time the intensity of orthorhombic microcrystals compacted by shock waves is 3-4 times higher than that of C lead fluoride.
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