Exciton interaction with Ce3+ and Ce4+ ions in (LuGd)3(Ga,Al)5O12 ceramics

Vasilii Khanin,Ivan Venevtsev,Kirill Chernenko,Vladimir Pankratov,Konstantin Klementiev,Thomas Van Swieten,Arnoldus J Van Bunningen,Ivan Vrubel,Roman Shendrik,Cees Ronda,Piotr Rodnyi,Andries Meijerink

doi:10.1016/j.jlumin.2021.118150

Abstract

Scintillators based on Ce-doped garnets are regularly co-doped with Mg2+ or Ca2+ to form Ce ions in 4+ state and reduce undesired afterglow. However overly high Ce4+ concentration leads to poor light yield performance. In order to understand the reason for variation in luminescence efficiency of Ce3+- and Ce4+-doped garnets we investigate the differences in energy conversion processes in complex LuGd2Ga3Al2O12:Ce3+/Ce4+ ceramics by means of VUV synchrotron irradiation. At first we have established via transmission spectroscopy and X-ray absorption spectroscopy that LuGd2Ga3Al2O12:Ce, Mg sample contains cerium in the 4+ state only. Then we show with VUV spectroscopy efficient interaction of excitons with Gd3+ and Ce3+, and lack of exciton absorption edge in LuGd2Ga3Al2O12:Ce4+ excitation spectrum. Instead, Ce4+ exhibits charge-transfer absorption band in the range of exciton emission. We suggest that when Ce4+ concentration becomes too high, the exciton → Gd3+ → Ce3+ energy transfer path is hindered. It leads to high intensity of Gd3+ luminescence in Lu1Gd2Ga3Al2O12:Ce, Mg ceramics, but lowered Ce3+ X-ray excited luminescence. Fine balance between 3+ and 4+ Ce concentrations is necessary to achieve the best performance of garnet scintillators.

Highlights

Cerium doped complex garnets are actively investigated for scintil lator [1] and persistent phosphor [2] applications
It has been shown that excitonic emis sion can be distorted/quenched by the absorption bands of doped species (Ce3+ [21], Nd3+ [36], Pr3+ [22], Gd3+ [25,37]), which leads to exciton → dopant energy transfer
From the difference between excitation spectra of LuGd2Ga3Al2O12:Ce and LuGd2Ga3Al2O12:Ce, Mg we propose that Ce4+ interacts neither with Gd3+ nor with excitons in ways that lead to luminescence

Summary

Introduction

Cerium doped complex garnets are actively investigated for scintil lator [1] and persistent phosphor [2] applications. In GGAG:Ce, Ca [16], GGAG:Ce, Mg [17,18] co-doping with Ca2+, Mg2+ above 0.1% leads to lower light yield by factor of 1.3–2. Doping YAG with RE ions significantly distorts and quenches exciton emission Addition of Ce4+ potentially creates an exciton quenching channel (by CT absorption) that lowers the probability of exciton → Ce3+/Gd3+ energy transfer. We consider it important to study exciton interplay with Ce3+, Ce4+ and Gd3+ ions in complex garnets. In the current work we investigate the differences in energy migra tion processes in complex Lu3Ga3Al2O12 and LuGd2Ga3Al2O12 garnet ceramics doped with Ce3+ or Ce4+ ions. We study the differences in excitation spectra of LuGd2Ga3Al2O12:Ce4+ and LuGd2Ga3Al2O12:Ce3+ lumines cence in the 4.5–10 eV range under synchrotron irradiation

Materials and experimental

Results and discussion

Conclusions