Luminescent and morphological studies of Tm-doped Lu₃Al₅O₁₂ and Y₃Al₅O₁₂ fine powders for scintillator detector application

Abstract

This work reports on the synthesis of Tm³⁺-doped Lu₃Al₅O₁₂ and Y₃Al₅O₁₂ fine powders by Pechini method searching for the enhancement of blue emission for scintillator detector application. The polymeric resin obtained as precursor was heated under 800–1100 °C, leading to cubic single-phase crystalline fine blue luminescent phosphors, independently on the thermal treatment or tested cation host. The mean crystallite size and diameter particles were estimated in the range of 20–30 and 20–130 nm, respectively. All emission spectra ($\text{λ}{}_{\mathrm{<mtext>ex</mtext>}}\text{=355}\text{nm}$) show strong blue emissions at 460 and 480 nm corresponding to the Tm³⁺ transitions ${}^1\text{D}{}_2\text{→}{}^3\text{F}{}_4$ and ${}^1\text{G}{}_4\text{→}{}^3\text{H}{}_6$, with lifetime decays in the range of microseconds. No red transitions are observed, but under 347 nm excitation Lu₃Al₅O₁₂ and Y₃Al₅O₁₂ matrices present a large emission band centred at ∼500 nm. Therefore, the synthesis method used resulted on both matrices doped with Tm³⁺ suitable for the preparation of blue luminescent phosphors to be applied as scintillators.

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.