New Ln-metal–organic
frameworks (Ln-MOFs), {[Ln(2,7-NDS)(IP)(OH)(H2O)2]·mH2O}
n
[Ln = Sm 1, Eu 2, Gd 3, Tb 4, Dy 5, m = 0.5–0; 2,7-NDS = 2,7-naphthalenedisulfonate, and IP = 1H-imidazo[4,5-f][1,10]-phenanthroline)
were obtained by the hydrothermal method. The Ln-MOFs feature one-dimensional
double chain structures. The photoluminescent properties of these
complexes were investigated. Notably, the Eu-MOF exhibits a broad
excitation band from 250 to 400 nm in the UV–vis region, and
it presents red emission from the 5D0 → 7F
J
transitions (where J = 0–4) of the Eu3+ ion. It is noteworthy
that it still shows intense emission under near-visible irradiation
at 350 nm < λex < 385 nm. Using the Eu-MOF
as a luminescent sensor, the detection of Fe3+/Ag+ and ornidazole (ODZ)/ronidazole (RDZ) in aqueous medium was realized
with long excitation wavelengths of 368 nm or even 385 nm in the near-visible
region. This work provides a new approach to designing an efficient
red emission with broad-band and near-visible light excitation and
with luminescent chemosensor capability for biological applications.
In addition, the Eu-MOF red light incorporated Gd-MOF blue-green light,
and a white-light emission is realized based on a two-component Gd0.99803Eu0.00197 doped complex. Magnetic studies
of the Dy-MOF reveal that it has a single-molecule magnet and slow
magnetic relaxation behavior with an energy barrier U
eff of 82.39 K.