Luminescent and morphological studies of Tm-doped Lu3Al5O12 and Y3Al5O12 fine powders for scintillator detector application
Introduction
Inorganic scintillators play an important role in radiation detection in many sectors of research concerning almost all medical diagnostic imaging modalities that use X-ray or gamma rays, and also in many industrial measuring systems [1]. The detection sensitivity in X-ray imaging techniques, so, can be greatly enhanced by using green or blue emitters, which offers several advantages, such as real-time imaging and less time exposure of the patient to the hazardous radiation [2]. In the different applications, the usual detector requirements are fast response time (10–100 ns), high light yield, high density (ρ) and high atomic number (Z) [3].
Host lattices, such as yttrium or lutetium aluminates containing rare earth ions as luminescent activators, in special cerium (Ce3+), have been investigated because the parity-allowed 4f–5d transitions of Ce3+ ion yield fast (∼ns) optical transitions that are highly desirable for scintillator detector application that requires green or blue emitters [4]. On the other hand, Tm3+ ion, even presenting forbidden Lapporte 4f–4f transitions [5] in the blue region, may also represents a good candidate for scintillators. Tm3+-doped yttrium or lutetium aluminates, for instance, have been studied mainly as a cathode ray tube phosphor or laser material, with extensive research performed in the near-IR and red spectral ranges [6]. Moreover, many studies have been employed in order to enhance the blue emission in Tm3+-doped compounds, such as the use of Li3+ as co-activator in Tm3+-doped Y3Al5O12 phosphor. Therefore, this work reports on the synthesis of Tm-doped Lu3Al5O12 and Y3Al5O12 fine powders by Pechini method, that has been commonly used to obtain oxides and oxossalts fine powders [7], [8], searching for the enhancement of blue emission for scintillator detector application.
Section snippets
Experimental procedure
Rare earth (Lu3+ or Y3+ and Tm3+) and aluminum nitrates were mixed with citric acid in appropriate stoichiometry, Tm3+: Lu3+ or Y3+ (mol%) = 0.25, 0.5 and 1.0%. The mixture was heated and stirred in a hot plate at 60 °C, and then ethylene glycol was added and heated at 90 °C, resulting on a polymeric resin (polyester). The yellowish resin was fired at ∼480 °C. Although the organic matter decomposes at 600 °C, in order to obtain luminescent and crystalline powders the fired resin was heated in the
Results and discussion
The XRD patterns of the synthesized powders, Lu3Al5O12:Tm and Y3Al5O12:Tm, heat treated under 800–1100 °C, Fig. 1, show a full set of well-defined Bragg reflections indicating that the specimens under study were a well-crystallized single-phase corresponding to cubic system of Lu3Al5O12 and/or Y3Al5O12 [10], independently on the used temperature. Moreover, the comparison among the diffractograms considering each doped matrices separately obtained under different temperatures shows that the half
Conclusion
Blue emitting Tm3+-doped Lu3Al5O12 and Y3Al5O12 fine powders to be applied as scintillators were successfully prepared by Pechini method. The compounds present very well crystalline single-phase of the cubic system with diameter particles and mean crystallite size in the range of 20–130 nm and 20–30 nm, respectively. Strong blue emissions at 460 and 480 nm are observed with lifetime decays in the range of microseconds.
Acknowledgements
We thank the Brazilian agency FAPESP for financial support.
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