Hydrothermal crystallization of a Ln₂(OH)₄SO₄·nH₂O layered compound for a wide range of Ln (Ln = La–Dy), thermolysis, and facile transformation into oxysulfate and oxysulfide phosphors

Abstract

Ln-Dependent crystallization, structure, and thermolysis were systematically studied for layered Ln2(OH)4SO4·nH2O compounds, and their transformation into oxysulfate and oxysulfide phosphors was demonstrated.

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

“…This rationalization was supported by the fact the 241-LRHs of Tb and Dy can be produced at 100 ℃ under the lower pH of 7, since a lower pH suppresses the hydrolysis of Ln 3+ [24]. The lattice parameters (a, b, and c), cell volume, and axis angle of the 241-LRHs across the lanthanide series (Ln = La-Dy) monotonously decrease as the size of Ln 3+ decreases [24]. The particle morphology was found to be significantly affected by the solution pH.…”

“…For example, under the same hydrothermal conditions of 100 ℃ and pH = 9, the larger Ln 3+ of La-Gd crystallized as 241-LRHs while the smaller ones of Tb 3+ and Dy 3+ were formed as the more OH  containing 251-LRHs of Ln 2 (OH) 5 (SO 4 ) 0.5 ·nH 2 O owing to their higher extent of hydrolysis [24]. This rationalization was supported by the fact the 241-LRHs of Tb and Dy can be produced at 100 ℃ under the lower pH of 7, since a lower pH suppresses the hydrolysis of Ln 3+ [24]. The lattice parameters (a, b, and c), cell volume, and axis angle of the 241-LRHs across the lanthanide series (Ln = La-Dy) monotonously decrease as the size of Ln 3+ decreases [24].…”

“…We recently proposed hydrothermal reaction for the controlled crystallization of 241-LRHs, using Ln nitrate and (NH 4 ) 2 SO 4 as the reactants, and successfully extended this family of compounds to the larger Ln 3+ of La and smaller Ln 3+ of Dy [24]. Reaction temperature and solution pH were identified as two most influential factors that determine the phase constituent of the hydrothermal product [24], which can also be understood in view of lanthanide contraction. For example, under the same hydrothermal conditions of 100 ℃ and pH = 9, the larger Ln 3+ of La-Gd crystallized as 241-LRHs while the smaller ones of Tb 3+ and Dy 3+ were formed as the more OH  containing 251-LRHs of Ln 2 (OH) 5 (SO 4 ) 0.5 ·nH 2 O owing to their higher extent of hydrolysis [24].…”

“…The former technique seems limited to intermediately sized Ln 3+ , and a series of single-phase 241-LRHs (Ln = Pr-Tb) have been synthesized through homogeneous hydrolysis of Ln sulfates in the presence of hexamethylenetetramine [8]. We recently proposed hydrothermal reaction for the controlled crystallization of 241-LRHs, using Ln nitrate and (NH 4 ) 2 SO 4 as the reactants, and successfully extended this family of compounds to the larger Ln 3+ of La and smaller Ln 3+ of Dy [24]. Reaction temperature and solution pH were identified as two most influential factors that determine the phase constituent of the hydrothermal product [24], which can also be understood in view of lanthanide contraction.…”

“…Reaction temperature and solution pH were identified as two most influential factors that determine the phase constituent of the hydrothermal product [24], which can also be understood in view of lanthanide contraction. For example, under the same hydrothermal conditions of 100 ℃ and pH = 9, the larger Ln 3+ of La-Gd crystallized as 241-LRHs while the smaller ones of Tb 3+ and Dy 3+ were formed as the more OH  containing 251-LRHs of Ln 2 (OH) 5 (SO 4 ) 0.5 ·nH 2 O owing to their higher extent of hydrolysis [24]. This rationalization was supported by the fact the 241-LRHs of Tb and Dy can be produced at 100 ℃ under the lower pH of 7, since a lower pH suppresses the hydrolysis of Ln 3+ [24].…”