Barium hafnate, BaHfO₃ is a valuable host lattice for X-ray phosphors, especially due to its high absorption for ionizing radiation, which results mailny from the presence of two heavy ions, Ba²⁺ and Hf⁴⁺ in the lattice and density reaches 8.5g/cm³. What is also advantageous is that BaHfO₃ crystallizes in cubic structure, which allows for transparent ceramics fabrication. These are potentially attractive replacements for monocrystallline materials.

Till now research on BaHfO₃ was concentrated on Ce-doped powders, because of its fast luminescence decay, so important in dynamic medical techniques. We choose doping with Eu as its red luminescence fits perfectly the region of the highest efficiency of CCDs, which is presently considered a detector of choice for digital planar X-ray imaging. In this technique the relatively slow decay of the Eu³⁺ luminescence is not an obstacle.

BaHfO₃:Eu(x%) powders were prepared with ceramic method. The products were examined with XRD technique, SEM, luminescence spectroscopy, synchrotron radiation, radioluminescence.

Analysis of the X-ray diffraction patterns of all samples (Fig.1) suggested that the dopant is distributed between both Ba²⁺ and Hf⁴⁺ sites. Yet, for low concentration the fractions of Eu which go the two sites are different than for higher concentration. This conclusion gor support from the results of luminescence, site selective spectroscopy, which allowed us to identify emission lines coming from Eu³⁺ located in Ba²⁺ site, as well as occupying the Hf⁴⁺ location, and showed that relative intensities of luminescense from the two sites vary strongly mirroring the variation of the diffraction line position (Fig.1). Surprisingly, only the Eu(Hf) ions are active in radioluminescence, while Eu(Ba) are being unable to intercept energy deposited in the host by X-rays.

Fig. 1. Eu concentration dependance of the position of diffraction line and variation of the intensities of the emission from two sites.

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