Well-defined crystallites autoclaved from the nitrate/NH4OH reaction system as the precursor for (Y,Eu)2O3 red phosphor: Crystallization mechanism, phase and morphology control, and luminescent property

Sulfate Exchange of the Nitrate-Type Layered Hydroxide Nanosheets of Ln2(OH)5NO3·nH2O for Better Dispersed and Multi-color Luminescent Ln2O3 Nanophosphors (Ln = Y0.98RE0.02, RE = Pr, Sm, Eu, Tb, Dy, Ho, Er, and Tm)

“…The strong and sharp 220 diffraction, arising from the ab plane (the hydroxide main layer), suggests that the host layers of L(Y 0.98 Eu 0.02 )H are well crystallized. Compared with the thick LRH crystals synthesized under high temperature [21–31, 33, 34], the 002 diffraction has a substantially lower intensity relative to the 220 one, implying that the primary crystallites are much less developed along the c -axis or rather thin, as also confirmed later by TEM analysis. SO 4 2− exchange of NO 3 − shortens the interlayer distance, as perceived from the obvious shifting of the 00 l diffraction to a higher angle, and the basal spacing ( d 002 ) calculated from the center of the 002 peak is ~0.886 nm for NO 3 − -L(Y 0.98 Eu 0.02 )H and 0.841 nm for the SO 4 2− derivative.…”

“…Figure 1a compares XRD patterns of the NO 3 − -L(Y 0.98 Eu 0.02 )H and its SO 4 2− derivative. The NO 3 − -type exhibits the characteristic 00 l and non-00 l diffractions of Ln 2 (OH) 5 NO 3 · n H 2 O layered compounds [20–34]. The strong and sharp 220 diffraction, arising from the ab plane (the hydroxide main layer), suggests that the host layers of L(Y 0.98 Eu 0.02 )H are well crystallized.…”

“…As the direct product of solution synthesis is usually a precursor, the final phosphor oxide is thus frequently observed to have properties dependent on the characteristics of its precursor [2]. Layered rare-earth hydroxide (LRH), as a relatively new type of anionic layered compounds [20], has attracted much attention during the recent years owing to its unique combination of the layered structure and the abundant optical, magnetic, and catalytic properties of the rare-earth elements [21–34]. The crystal structure of Ln 2 (OH) 5 A· n H 2 O LRH (Ln = rare-earth; A  = NO 3 − or halogen anion; n  ~ 1.5) can be viewed as an alternative stacking along the c -axis ([001] direction) of the positively charged hydroxide main layers containing Ln 3+ and exchangeable A anions located in the interlayer for charge balance.…”

“…The crystal structure of Ln 2 (OH) 5 A· n H 2 O LRH (Ln = rare-earth; A  = NO 3 − or halogen anion; n  ~ 1.5) can be viewed as an alternative stacking along the c -axis ([001] direction) of the positively charged hydroxide main layers containing Ln 3+ and exchangeable A anions located in the interlayer for charge balance. The well-established synthetic methodologies of hydrothermal reaction [25–34] and reflux growth [21–24] generally produce platelike LRH crystals of several microns in lateral dimension and tens to hundreds of nanometers in thickness, for which single layer or few-layer thick nanosheets can only be obtained by swelling the pristine crystals via exchange of the interlayer anions with significantly larger ones (such as dodecyl sulfate, DS − ), followed by exfoliation in a proper medium (such as formamide) under mechanical agitation [35–39]. Exfoliation, however, is well known to be time consuming, frequently incomplete, and usually accompanied by fragmentation of nanosheets.…”

Recent progress in layered rare-earth hydroxide (LRH) and its application in luminescence

“…The LRH crystals synthesized with NH 4 NO 3 as a mineralizer, having a lateral size of ~300 μm and a thickness of ~9 μm (Fig. 2(a)) [18], are attractive starting crystals for the exfoliation of ultra-large nanosheets, but successful insertion of DS  anions into the interlayers is rather challenging at room temperature owing to the very large crystal size. We recently proposed hydrothermal exchange of the interlayer NO 3  for so large LRH crystals, and through kinetics study a "wriggle intercalation" model was proposed for the DS  anions (Fig.…”