ABSTRACT
PhosphorsThe low (0.5-1 keV) and high (20-30 keV) voltage cathodoluminescence modes including color CL and PL with different excitation wavelengths (147, 254, 365 nm) were applied to investigate the lu-minescence properties and the energy transfer processes in CaWO4, activated by trivalent rare earth Eu and Tb ions. Photoluminescence characteristics were estimated on the basis of emission and excitation spectra registered at room temperature (Xe 500 W lamp) with DARSA PRO 5100 PL System (Diode Array Rapid Scan Analysis – Professional Scientific Instrument Co., Korea). The excitation was performed with a 254 nm UV radiation as well as 365 nm. Low-temperature PL measurements (15 K) were also used to
explain the energy transfer mechanism. He-Cd laser with excitation wavelength of 325 nm (55 mW) was applied as a light source. To verify the luminescence properties of synthesized CaWO4:Eu3+, Tb3+ phosphor in a large range of excitations, low-voltage CL was carried out at excitation energy of 0.5-1 keV by using a Kimball Physics FRA2X1-2/EGPS-2X1 electron gun system. High-voltage 5-40 keV local CL measurements were performed with a special CL spectrometer, combined with a standard “Camebax” [178] (Fig. 3.24). Surface investigation and distribution the luminescence centers in powders were carried out with color CL using a special attachment for CCL-SEM [154] (Fig. 3.7).Both the monochromatic and panchromatic CCL-SEM modes are used. At the monochromatic mode the CL emission was detected at definite wavelength. At the panchromatic CL-mode the CL was recorded at all the visible emission spectrum. By this way, monochromatic CL corresponds to definite transitions between the defect levels attributed to the activator. Spatial distribution of the monochromatic (Fig. 4.1) or panchromatic (Fig. 3.6) CL on the surface under study was recorded in forms of corresponding CCL maps. A variety of colors observed in a panchromatic CCL map shows, therefore, a spatial distribution of all the luminescent centers that occurred by nature or design on the surface of investigated phosphors (Fig. 3.6).
