The Interpretation of Broadened Gd³⁺ EPR Spectra of Polycrystalline Ceramics

Abstract

An interpretation is given of the broadened EPR spectra of Gds+ ions, which are frequently observed in polycrystalline ceramics and glasses. A reasonable simulation of the spectra is obtained, when these are regarded as a superposition of a large number of normal EPR powder spectra, each of which can be described with the usual spin-Hamiltonian. These originate from the many different surroundings of the Gd3+ ions in these compounds due to the structural disorder. The result is, that only those transitions, which are independent of the zero field splitting parameters in the spin Hamiltonian, remain visible in the derivative spectrum. The interpretation is supported by the EPR powder spectrum of the Gd3+ doped compound CaHf,O,, which changes from broadened into clearly resolved, when the compound is ordered by an annealing process.Eine Interpretation wird fur die verbreiterten EPR-Spektren von Gd3 +-Ionen gegeben, die hLufig in polykristalliner Keramik und Glasern beobachtet werden. Eine ziemlich gute Simulation dieser Spektren wird erhalten, wenn diese Spektren als Summe einer groBen Anzahl normaler EPRSpektren betrachtet werden, welche mit dem ublichen Spin-Hamiltonoperator beschrieben werden konnen. Die normalen Spektren werden von den vielen verschiedenen Umgebungen der Gd3+-Ionen verursacht, als Folge der strukturellen Unordnung in diesen Verbindungen. Das Ergebriis ist, da13 nur solche Resonanzen wahrnehmbar sind im abgeleiteten Spektrum, die unabhangig von den Parametern der Nullfeldaufspaltung im Spin-Hamiltonoperator sind. Diese Interpretation wird durch das Verhalten des EPR-Spektrums eines Polykristalls der Gd3+-dotierten Verbindung CaHf,O, gesttitzt. Das erst verbreiterte Spektrum andert sioh in ein deutlich aufgespaltenes Spektrum, wenn die Verbindung in einem TemperungsprozeB geordnet wird.

An electron spin resonance and photoluminescence investigation of the effect of annealing temperature on Gd-doped La2Zr2O7 nano-ceramics

“…Koopmanas et al [32] assigned the g$ 6.0 feature to Gd 3 þ ions subjected to an intermediate crystal field strength of axial symmetry whereas the broadness of the ESR spectrum was attributed to presence of isolated rare earth ions located in different sites. Nicklin et al [30] attributed all the principal features of the "U" spectrum to the presence of Gd 3 þ ions at three distinct sites in glassy matrix (soda rich, silica rich and diffuse transition region).…”

“…The spectrum consisted of three prominent features with effective 'g' values $ 6.0, $ 2.8 and $ 2.0 superimposed on a broad resonance line shape that encompasses the prominent feature at g$ 2.0. This type of spectrum has been labeled the "U" spectrum (U¼ ubiquitous) reported in vitreous materials [29,30] as well as in disordered polycrystalline materials such as zeolites [31] and PLZT doped with low concentrations of Gd 3 þ ions [32].…”

EPR Study of Gadolinium(III) Complexes with Heteropolyanions: [Gd(SiW11O39)2]13-and [GdP5W30O110]12-

“…This type of spectrum has been labelled as a U-spectrum.in view of its'.ubiquity in vitreous materialS [8] and in polycrystalline materials such as zeohtes [9] and ceramics [10]. The first interpretation of the g 6.0 feature of the U spectrum was '…”

Electron paramagnetic resonance and optical absorption spectra of Gd3+ ions in alkali cadmium borosulphate glasses

“…Cugunov and Kliava [13] attributed the g x 6.0 feature to a strong and well-defined rhombic crystal field and the broad resonance encompassing the g w 2.0 feature to clusters of Gd3+ ions. Koopmans et al [16] specifically assigned the g z 6.0 feature to intermediate crystal field strength sites of axial symmetry and attributed the broadened general appearance of the U-spectrum to isolated rare-earth ions at a wide variety of sites.…”