Characteristic Coordination Structure around Nd Ions in Sol–Gel-Derived Nd–Al-Codoped Silica Glasses

Abstract

Al codoping can improve the poor solubility of rare-earth ions in silica glasses. However, the mechanism is not well understood. The coordination structure around Nd ions in sol-gel-derived Nd-Al-codoped silica glasses with different Al content was investigated by optical and pulsed electron paramagnetic resonance spectroscopies. Both tetrahedral AlO4 and octahedral AlO6 units were observed around Nd ions as ligands. The average total number of these two types of ligands for each Nd(3+) ion was ∼ 2 irrespective of Al content and was larger by 1-2 orders of magnitude than that calculated for a uniform distribution of codopant ions (∼ 0.08-0.25). With increasing Al content, AlO4 units disappeared and AlO6 units became dominant. The preferential coordination of AlOx (x = 4, 6) units to Nd ions enabled the amount of Al necessary to dissolve Nd ions uniformly in silica glass at a relatively low temperature of 1150-1200 °C to be minimized, and the conversion of AlO4 units to AlO6 units around Nd ions caused the asymmetry of the crystal field at the Nd sites to increase and the site-to-site distribution to decrease.

Energy Transfer and Quenching in Sol–Gel‐Derived Silica Glass Green Phosphors Doped with Tb3+ and Ce3+ Ions: Distinct Difference between P‐ and Al‐Codoped Glasses

“…[ 45 ] Aluminum lactate (Al(lac) 3 ) is a less acidic Al source and was used to prepare Nd–Al‐codoped silica glasses with Al contents up to 2.5 at% with using imidazole as the base for the neutralization. [ 46 ] However, Al(lac) 3 was unusable for the Tb–Al‐codoped system because viscous precipitates were formed in the aqueous solution of Al(lac) 3 , terbium acetate, and imidazole. The precipitate formation was suppressed by using the 1:1 mixture of Al(NO 3 ) 3 and aluminum acetohydroxamate (Al(aha) 3 ), probably because of the high coordination strength of acetohydroxamate ligands to Al.…”

“…In sol–gel‐derived Nd–Al‐codoped silica glasses prepared by us at the Al to Nd molar ratio of 0.8–2.5, the average number of AlO x units coordinated to a Nd 3+ ion is ≈2. [ 46 ] This value is one to two orders of magnitude higher than that in conventional RE–Al‐codoped silica glasses with uniform Al distribution. [ 34 ] Such metastable Nd–Al pairs may be formed in precursor solutions and preserved in the resulting silica glasses because of relatively low sintering temperatures (≈1200 °C).…”

“…We have developed cosolvent‐free sol–gel processes to prepare RE − P‐ and RE − Al‐codoped silica glasses without using alcohols, organic solvents, and other nonessential additives. [ 39–46 ] The RE − P‐codoped silica glasses prepared in this way at P to RE molar ratio at ≳1 [ 40 ] are transparent glass‐ceramics containing REPO 4 nanocrystals with diameters of ≈5–10 nm. [ 41–44 ] The concentration of RE ions in REPO 4 crystals is as high as 1.3–1.6 × 10 22 cm −3 , [ 47,48 ] and the small distances between adjacent RE ions (≈0.4 nm) enable rapid energy transfer between them.…”

Tailoring the luminescence of Eu3+ co-doped Dy3+ incorporated aluminofluoro-borophosphate glasses for white light applications

“…The Ω 4 and Ω 6 parameters are related to the bulk properties such as viscosity and rigidity of the glasses. Higher values of Ω 4 parameter indicate higher rigidity [33] and lower Dy-O bond covalency [15] in the prepared glasses.…”

“…This increases the transition probability of the hypersensitive transitions (electric dipole transitions) in RE 3 þ ions. Addition of Al 2 O 3 creates more number of non-bridging oxygens in the glass network which creates more number of vacancies for a given RE 3 þ ion [15,16]. Phonon energy and water absorption property of the boro-phosphate glasses were reduced by the addition of ZnF 2 .…”