Glass forming regions and concentration-dependent luminescence properties of Tb³⁺-activated tellurium-lutetium-tungsten glasses

Highlights

• The glass-forming regions of tellurium-gadolinium-tungsten ternary system prepared at 1000 °C for 60 min.

• The concentration of Tb³⁺ ions is optimized in tellurium-lutetium-tungsten glasses.

• The energy transfer among Tb³⁺ ions is determined to the electric dipole–dipole interaction.

• Tb³⁺-activated tellurium-lutetium-tungsten glass is characterized with the density of 6.49 g/cm³ and the lifetime of 0.551 ms.

Abstract

The glass-forming regions of tellurium-gadolinium-tungsten ternary system prepared at 1000 °C for 60 min were firstly determined. To improve density, the full replacement of lutetium for gadolinium to form Tb³⁺-activated tellurium-lutetium-tungsten glasses with the composition of 64TeO₂-20WO₃-(16–y)Lu₂O₃-yTb₂O₃ were designed for scintillation application. The concentration-dependent optical properties of Tb³⁺-activated tellurium-lutetium-tungsten glasses were fully investigated by transmittance, excitation and emission spectra, together with the luminescence decay curves. The energy transfer mechanism was discussed according to Huang's rule. The optimized 4 mol% Tb₂O₃ activated tellurium-lutetium-tungsten glasses with the density of 6.49 g/cm³ and the lifetime of 0.551 ms are developing to be suitable for the potential detection of slow events in the future work.

Introduction

Glass scintillators, that convert high-energy rays (such as X-, α-, β- and γ-rays) into the visible or ultraviolet light, are extensively studied in view of the attractive advantages of low cost, large-volume production and easy shaping of elements.¹ The density of a glass scintillator is always preferred to be higher than 5.0 g/cm³ for its potential application in the aspects of high-energy physics and medical image engineering. Because dense glass scintillators can effectively absorb the incident high-energy rays and improve its luminescence efficiency.² There are reports on kinds of borosilicate,3, 4, 5, 6, 7 borogermanate,8, 9, 10 germanate11, 12, 13 and tellurium^14,15 glasses with the density over 5.0 g/cm³ in available literature. To our relief, the excellent silicate glass scintillator is expected for future calorimetry in CERN of Switzerland.^17,18 However, the melting temperature of the mentioned glass scintillators is usually in the 1300–1600 °C region except for the tellurium system. Although the melting-temperature of the tellurium glass scintillator containing 15 mol% PbF₂ and 10 mol% BaF₂ is reported to be lower than 900 °C,¹⁴ the intrinsic toxicity and inevitable scintillation quenching effect resulting from the lead ions could limit its further application.

In fact, the tellurium system with the structural variability is considered to be one of the most ideal host materials due to the unique combinations of optical and spectroscopic properties, together with their attractive environmental resistance and mechanical properties. The tellurium glass incorporated with rare-earth ions is suitable for broad spectral bandwidth materials, especially for laser and amplifier devices.¹⁹ However, the scintillation property of tellurium glass has been rarely reported.^14,15 Therefore, the pursuit of dense tellurium glass scintillator is of significance in both the scientific and practical aspects.

Therein, in this paper, we develop the tellurium-lutetium-tungsten glass scintillators activated with rare-earth ions for the following two aspects. On the one hand, the phonon energy (hw_max) of tellurium system with about 600–850 cm⁻¹ is considerably lower than those of the other germanate (800–975 cm⁻¹), silicate (1000–1100 cm⁻¹), phosphate (1100 cm⁻¹) and borate (1400 cm⁻¹) inorganic system.²⁰ To some extent, it means that the probability of non-radiative decay from the incorporated rare-earth ions will get low, thus enhancing the radiation probability and resulting in the higher luminescence efficiency.²¹ On the other hand, the excellent physical properties of TeO₂ with both the density of 5.670 g/cm³ and the melting point of 732.6 °C are also beneficial to optimizing the tellurium glass scintillator.

Our work, accordingly, is divided into two parts. Firstly, the glass-forming region of TeO₂-Gd₂O₃-WO₃ ternary system was determined for the first time, and Tb³⁺-activated tellurium-lutetium-tungsten glasses were simply prepared by fully replacing Gd₂O₃ with Lu₂O₃ for the purpose of enhancing glass density. Secondly, the concentration-dependent optical properties were fully investigated by characterizations including transmittance, excitation and emission spectra, together with luminescence decay curves.