RE(OH) 2 NO 3 (RE = Tb, Dy, Ho, and Er): Synthesis and Nonlinear Optical Properties of Water-Resistant Lanthanide Hydroxide Nitrates.

A series of lanthanide-containing water-resistant nitrates, namely RE(OH) ₂ NO ₃ (RE = Tb( 1 ), Dy( 2 ), Ho( 3 ), and Er( 4 )), was obtained through the hydrothermal process. As possible nonlinear optical materials, they feature a layered isomorph composed of an [REO ₃ (OH) ₆ ] polyhedron and an [NO ₃ ] triangle, and the synergistic arrangement of the [REO ₃ (OH) ₆ ] and [NO ₃ ] groups in their structures leads to their obvious second-order nonlinear optical effect. Nevertheless, the unique optical absorption caused by the electronic transitions on 4f-4f orbitals of lanthanides results in their second harmonic generation responses of different strengths, with 1 exhibiting 5.07 times that of KDP, but 2 - 4 showing less than half of KDP. In addition, 1 possesses an outstanding water-resistant capacity and a transparent cut-off edge around 300 nm, foreshadowing its potential value as a nonlinear optical crystal. Moreover, 1 is found to emit characteristic green fluorescence due to the typical ⁵ D ₄ → ⁷ F ₅ transitions of the excited Tb ³⁺ ions.