Dancho Tonchev

Oxy-fluoride glasses containing strontium carbonate doped with samarium have been prepared. The glasses are sorted with respect to the quantity of strontium carbonate. The fluorescence spectra recorded for different pumping wavelengths are presented. We have investigated the influence of the excitation on the efficiency of the fluorescence, depending on the quantity of strontium carbonate in the samples for a variety of excitation wavelengths. The results of optical pumping in the range 370 - 490 nm show a typical fluorescence spectrum of Sm3+. When pumped with wavelengths above 500 nm a new peak that has not been reported appeared in the fluorescence spectrum. From the data analysis the range of appearance of the fluorescence peak was determined and the most efficient source for its excitation was found.

There is a special need to develop a dosimetry technique with a large‐dynamic range and high‐spatial resolution to characterize the microstructured X‐ray beams used in microbeam radiation therapy ( MRT ) for cancer. We report the synthesis and characterization of oxyfluoride glass‐ceramic (SiO ₂ –Al ₂ O ₃ –CaF ₂ –CaO–SmF ₃ ) plates, which contain trivalent‐samarium‐doped calcium fluoride (CaF ₂ :Sm ³⁺ ) nanocrystals, for use as a dosimetric detector material, particularly for MRT applications. Our approach utilizes the extent of Sm ³⁺ →Sm ²⁺ valence reduction caused by X‐ray irradiation as a probe of the X‐ray dose delivered; and confocal fluorescent microscopy is used to read out the distribution of valence reduction through the photoluminescence ( PL ) signal. Our study showed that the Sm ³⁺ →Sm ²⁺ valence reduction takes place in CaF ₂ nanocrystals, but not in the glass matrix. The Sm ²⁺ shows PL emission predominantly due to the fast 4 f ⁵ 5 d ¹ → ⁷ F ₀ transition, which allows us to read out the detector plate at a high scanning speed. Further, our experiments showed that the detection dose range reaches several thousands of grays, and X‐ray dose distribution is detected at a micrometer scale. In addition, the Sm ²⁺ signal can be erased either by heating the irradiated sample at a suitable high temperature or by exposing it to UV light; and the erased glass‐ceramic plate is reusable. The new Sm‐doped oxyfluoride glass‐ceramic with CaF ₂ nanocrystals reported in this work shows potential for practical use in high‐dose and high‐resolution dosimetry for MRT .