Elsevier

Journal of Alloys and Compounds

Volume 581, 25 December 2013, Pages 801-804
Journal of Alloys and Compounds

High light yield Ce3+-doped dense scintillating glasses

https://doi.org/10.1016/j.jallcom.2013.07.181Get rights and content

Highlights

  • Ce3+-doped dense scintillating glasses containing Gd2O3 and Lu2O3 were prepared.

  • Increasing the concentration of Gd2O3 and Lu2O3 can increase the light yields.

  • The highest light emission intensity excited by X-ray is 87% of BGO.

  • The decay time constants are in the range of 30–40 ns.

  • The energy transfer from Gd3+ to Ce3+ plays an important role in the glasses.

Abstract

Dense scintillating glasses containing 15 mol% BaF2 and different molar concentrations of heavy rare earth metal oxides Gd2O3, Lu2O3, La2O3 activated by Ce3+ are studied. Absorption, excitation, and luminescence spectra are presented. Mechanisms of these glasses are discussed. We observed that energy transfer from Gd3+ to Ce3+ plays an important role in the scintillation mechanism of these glasses and the optimum concentration of Gd2O3 is found to be approximately 15%. Also, increasing the concentration of Lu2O3 and La2O3 appears can increase the scintillation light yield and the glass density. The highest integrated light emission intensity of these glass samples excited by X-ray is 87% of BGO and the decay time constants are in the range of 30–40 ns, much shorter than the 300 ns decay time of BGO. The 15 mol% BaF2, which replaces lighter compounds SiO2 and B2O3 as one of the important ingredients of the oxyfluoride glasses that we studied, can increase the density of the glasses and also improve the light yield. Densities of glass samples that we made are from 5.1 to 6.2 g/cm3.

Introduction

Scintillating glasses are alternatives to inorganic single crystal scintillators for applications in high energy physics experiments and gamma ray medical imaging (PET and SPET) [1]. The main advantages of scintillating glasses lie in the possibility of low production cost and ease of manufacturing for different sizes and shapes, such as optic fibers. Detecting high energy particles and gamma rays usually require high density scintillators with high light yield and fast decay time. Densities of commonly used single crystals [2] such as NaI(Tl), CsI(Tl), LaBr3, BGO, LSO, LYSO, are in the range of 3.7 g/cm3 for NaI to 7.4 g/cm3 for LSO. The light yields of these crystal scintillators range from 8000 γ’s/MeV for BGO to 65,000 γ’s/MeV for LaBr3 and the decay time constants range from 25 ns for LaBr3 to 1.3 μs ns for CsI.

The scintillating glass SCGC-1C was commonly used in high energy physics experiments in the 1980s [3]. The density of this glass with 44 mol% BaO and 42 mol% SiO2 doped with 1.5% Ce2O3 is only 3.5 g/cm3 and its scintillation light yield is 400 γ’s/MeV or ∼5% of that of BGO that is typical for Ce3+ doped dense scintillating glasses. In the 1990s that motivated by the need of the CMS electromagnetic calorimeter at LHC [4], intense efforts were devoted to develop higher density fast scintillating glasses. The CMS EM calorimeter required approximately 10 m3 high density and fast scintillating materials. As one of the candidates, HMF glasses was developed that contained significant amount of HfF4 and BaF2 doped with 5% CeF3 and the density of this glass could reach ∼6 g/cm3 was achieved [4]. Dense glasses containing high concentration of gadolinium oxide with Ce2O3 doping and density up to 5.5 g/cm3 was developed [5]. The light yields of both types of scintillating glasses were rather low, only a small fraction of the light yield of BGO. The CMS experiment [6], [7] eventually selected PbWO4 single crystal that has density of 9.1 g/cm3 for its EM calorimeter.

In recent years, a total absorption calorimeter concept that can significantly improve the performance of future high energy calorimeters was proposed. This concept would require on the order of 100 m3 dense scintillating materials. A suitable scintillating material that is inexpensive to fabricate is very critical for realizing this concept. With this application in mind, we have setup a dense scintillating glass development program. Early results of gadolinium oxide based dense scintillating glasses were reported three years ago [8].

Aiming for X–CT applications, authors of Ref. [9] prepared samples of Eu3+-activated scintillating glasses with molar compositions of 35SiO2–15B2O3–30Ln2O3–20AlF3 (Ln = Y, La, Gd, Lu) and measured their properties. The decay time constant of the main scintillation peak at 612 nm was 1.2 ms, too slow for high energy physics experiments and some medical gamma ray imaging applications.

Most of heavy rare earth metal oxide hosts have large phonon energies in the range of 900–1400 cm−1 owing to the lattice vibrations of network-forming oxides. Some rare earth metal ions such as Gd3+ ions in glass matrixes do not quench the scintillation with appropriate doping. They can even help the scintillation process because the high energy transfer efficient through rare earth metal ions. Fluoride glasses have an advantage over oxide glasses due to their considerably lower phonon energies (typically below 600 cm−1) providing higher quantum efficiency for luminescence after doped with rare earth elements. In addition of lower phonon efficiency, [10] oxyfluoride heavy rare earth metal glasses and glass-ceramic systems have lower non-radiative transition probabilities that can also improve luminescence quantum efficiency.

In this paper, we report our recent results on Ce3+ doped gadolinium and lutetium oxyfluoride glasses. Lu2O3 based scintillating glasses that can be potentially denser than Gd2O3 based scintillating glasses. Oxyfluoride glasses containing La2O3 have also been tested.

Section snippets

Experimental procedures

Samples of Ce3+-activated dense scintillating glasses that contain concentrations of Gd2O3 and Lu2O3 up to 35 mol% with 15 mol% BaF2, 20 mol% SiO2 and various amounts of B2O3 were prepared. Luminescent properties of five such glass samples were studied. The effects of Gd3+ and Lu3+ ions on the scintillating properties under X-ray excitation have also been investigated. Luminescent properties of three glass samples containing La2O3 were also measured. The Ce3+ was introduced in the form of CeF3 and

Density and radiation length of various samples

High density and short radiation length of scintillators are particularly important for high energy physics experiment and medical imaging applications. Densities of six samples are listed in Table 1. All samples that contain different percentages of Lu2O3 and Gd2O3 have densities greater than 5 g/cm3. In particular, the density of S5 is higher than 6 g/cm3 with radiation lengths shorter than 1.5 cm making it an attractive candidate for high energy physics and medical imaging applications [11].

Absorption spectra

Conclusions

Dense scintillating glasses with molar compositions 20SiO2–(49−xyz)B2O3–15BaF2xLu2O3yGd2O3zLa2O3–1Ce2O3 (x  20, y  20, z  10) are studied. Activated by Ce3+ with 2 mol% CeF3 and sensitized by Gd3+ with ⩽15 mol% Gd2O3, we found that the energy transfer from Gd3+ to Ce3+ is efficient and played an important role in the scintillation process. Also, in addition of increasing the glass density, Lu2O3 and La2O3 appear can increase the scintillation light yields. The peak light emission intensities of

Acknowledgments

Project supported by Zhejiang Provincial Natural Science Foundation of China (Grant Nos. Z4110072, R4100364), the Natural Science Foundation of China (Grant Nos. 61275180, 50972061, 51272109), the Outstanding Dissertation Growth Foundation of Ningbo University (No. PY20120020), the Opening Foundation of Zhejiang Provincial Top Key Discipline (Nos. 20110934 and 20121139) and K.C. Wong Magna Fund in Ningbo University.

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