Synthesis, crystal structure and optical properties of Me(OH)(HCOO)2 (Me = Al, Ga)

Abstract

The formation conditions, crystal structure and luminescence properties of aluminum and gallium hydroxide diformates, Me(OH)(HCOO)₂, have been established. Both compounds crystallize in a monoclinic lattice (space group C2, #5 and Z = 8) with parameters: a = 8.8629(2) Å, b = 9.9890(2) Å, c = 10.2411(1) Å, β = 106.223(1)°, and V = 870.56(3) ų (Al) and a = 8.8746(1) Å, b = 10.3291(1) Å, c = 10.27870(9) Å, β = 105.7565(6)°, and V = 906.81(2) ų (Ga). The emission spectra of Me(OH)(HCOO)₂ under UV excitation with wavelength λ = 285 nm exhibit maxima in the range of 440–470 nm. The emission accompanied by light-blue luminescence is greatly enhanced when going from the aluminum to the gallium compound. The origin of intrinsic emission centers responsible for the luminescence properties of Me(OH)(HCOO)₂ is suggested and the higher emission of the gallium hydroxide diformate is substantiated by means of density-functional theory calculations.