Bright aspects of defects and dark traits of dopants in the photoluminescence of Er2X2O7:Eu3+ (X = Ti and Zr) pyrochlore: an insight using EXAFS, positron annihilation and DFT

Santosh K Gupta,Paramananda Jena,A K Yadav,K Sudarshan,S N Jha,P S Ghosh,D Bhattacharyya

doi:10.1039/d0ma00978d

Santosh K Gupta, Paramananda Jena + Show 5 more

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This work investigated the origin of blue PL in undoped and absence of Eu3+ red PL in the doped Er2X2O7 (X = Ti and Zr) pyrochlore using photon, positron and X-ray as spectroscopic probe and further complimenting with DFT.

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Density of state (DOS) calculations suggested that a possible reason for this is that the Eu f-states are dominantly distributed around the bottom edge of the valence band (VB), far from the Fermi energy, electronic band gap, and top edge of the VB actively participating in the electronic transitions
In this work, undoped and doped EZO, ETO, Eu3+-doped EZO (EEZO), and Eu3+-doped ETO (EETO) microcrystals with differing structures, defects, and ordering were synthesized using a ball-milling method
Synchrotron-based Extended X-ray absorption fine structure (EXAFS) measurements and Positron annihilation lifetime spectroscopy (PALS) suggested a large concentration of defects in both samples, the nature and concentration of defects in the zirconium material were quite different than in the titanium counterpart, with the possible formation of defect agglomerates and clusters in the former

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Introduction

Researchers worldwide have begun to look for an alternative to borosilicate glass In this context, A2B2O7 materials with various favourable properties, such as high radiation stability, negligible leaching, and the ability to accommodate large concentrations of lanthanides and actinides at both the A- and B-sites can be used as nuclear waste hosts.[14] A2B2O7 compounds exist in two different structures, viz., the ideal pyrochlore (IP) and disordered fluorite (DF) structures, which have the space groups Fd3%m and Fm3%m, respectively. Each structure has its own advantage; the IP structure is preferred for luminescence, thermal barrier coatings, and upconversion, whereas the DF structure is more suitable for nuclear waste hosts, catalysis, oxygen conductors in fuel cells, etc.[15] the defect density will be different in the two phases, which can have great implications on various properties such as magnetic, conductivity, and optical properties. We have explored Nd2Zr2O7 and Gd2Zr2O7, both of which exist in the DF structure, for self-activated emission, luminescence host and speciation of uranium.[16,17] La2Zr2O7 and La2Hf2O7 pyrochlores, due to their r(A3+)/r(B4+) ratios of greater than 1.46, exist in the IP structure, and have been explored for use as phosphors, scintillators, thermal sensors, etc.[18]

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