In
this article, we synthesized a Yb3+-doped two-dimensional
(2-D) upconverting Tb metal–organic framework (Tb-MOF) (hereinafter
referred to as Tb-UCMOF) by a one-step solvothermal method. The synthesized
Tb-UCMOF is composed of stacks of 2-D nanosheets with an average width
distributed between 250 and 300 nm, and these nanosheets can be exfoliated
by a simple liquid ultrasound method. The structural characteristics
of this flaky particle accumulation are confirmed by the type IV adsorption–desorption
isotherm with a H3-type adsorption hysteresis loop, and
the Brunauer–Emmett–Teller surface of Tb-UCMOF is 143.9257
m2·g–1. Tb-UCMOF has characteristic
emissions of Tb3+ which are located at 490, 545, 585, and
621 nm under 980 nm excitation. The upconverting luminescence mechanism
is attributed to that Yb3+ absorbs multiple photons and
transfers the energy to Tb3+, causing its 4f electrons
to jump to the excited state, and then the upconverting emissions
are obtained when electrons return to the ground state. Since the
Tb-UCMOF nanosheets have high dispersibility and an obvious upconverting
luminescent signal, we explored their luminescence sensing properties.
The luminescence intensity is found to gradually decrease with the
addition of Cu2+, the linear range of Cu2+ sensing
is 0–1.4 μM, and the detection limit is 0.16 μM.
This rapid, highly selective, and sensitive Cu2+ sensing
indicates that 2-D upconverting MOF nanosheets have great application
prospects in luminescence sensing and also promote the research of
2-D upconverting MOFs with specific recognition for the application
of biological and environmental luminescent sensors.