Bridgman‐Stockbarger growth and X‐ray photoelectron spectroscopy study of LiY_1‐xEu_xF₄ crystals

Abstract

Key words europium-doped lithium yttrium fluoride, Bridgman-Stockbarger growth, X-ray photoelectron spectroscopy, valence instability of europium. PACS 71.20. Ps, 73.20.At, 75.20.Ck, 81.10.Fq, 82.30.Lp LiY 1-x Eu x F 4 (x = 0; 0.1 nominally) crystals were obtained by a modified Bridgman-Stockbarger technique. Europium was found to coexist in the LiYF 4 :Eu crystal in two valence states, Eu 3+ and Eu 2+, the content of the latter being enhanced in the near-to-surface region. The presence of bulk divalent europium is attributed to a partial reduction of europium during crystal growth. Because of the presence of Eu 2+ , additional electronic states in the electronic gap of LiYF 4 were observed.

Dopant Concentration Induced Optical Changes in Ca,Eu-α-Sialon

“…According to references the two peaks at 1134.7 and 1124.4 eV in the XPS spectrum can be attributed to Eu 3+ and Eu 2+ 3d5/2 core levels, respectively [48,51,52] [48]. The XPS analysis suggests that the particle surface is significantly enriched in europium and it is present in both the Eu 2+ and Eu 3+ oxidation states.…”

“…Binding energy values were calibrated against the hydrocarbon C 1s line (eV), present because of contamination from ambient air or transport conditions [46][47][48]. Photoluminescence excitation and photoluminescence spectra were acquired using a FluoroMax-4P TCSPC spectrofluorometer produced by Horiba (Horiba Scientific, Kyoto, Japan), containing Czerny-Turner monochromators for excitation and emission.…”

“…We showed for the first time that the chemical composition of the surface layer of the phosphor particles deviates from the interior thus the luminescent properties of these materials would be altered by the fraction of the surface, namely the specific surface area. [48]. The XPS analysis suggests that the particle surface is significantly enriched in europium and it is present in both the Eu 2+ and Eu 3+ oxidation states.…”

Influence of the atmosphere on the growth of LiYF4 single crystal fibers by the micro‐pulling‐down method

“…Since the lattice constants will not change significantly by a slight oxidation of YF 3 the XRD spectra were misinterpreted by assigning the additional peaks (arrow in Fig. 3a) to YF 3 and therefore concluding erroneously that the white parts were due to incongruent melting [5,6]. There is nearly no axial segregation for the micro-pulling-down growth, in opposite to Bridgman or Czochralski growth, where one gets, because of an effective segregation coefficient k < 1, a first part of the crystal full of white precipitates followed by a clear part of the crystal.…”

“…Abell et al [2] reported congruent melting when using high purity starting material and purified Argon atmosphere while Thoma et al [3] showed in their phase diagram incongruent melting with peritectic point at 52 mol% LiF/48 mol% YF 3 . The Czochralski [4], Bridgman [5] and micro-pulling-down technique [6] have been used to grow LiYF 4 using an off-stoichiometric composition. However, except for the reported Czochralski growth [4], where the atmosphere was purified, the crystals contained some opaque part full of inclusions which have been assigned to YF 3 .…”