Ref.: MceMef32-004
Apresentador: Rubens Nicolas Leitão de Oliveira
Autores (Instituição): Oliveira, R.N.(Universidade Federal do Ceará); Palácio, M.P.(Universidade Federal do Ceará); Carmo, F.F.(Universidade Federal do Ceará); Nascimento, J.P.(Instituto federal do ceará); Sales, A.J.(Universidade Federal do Ceará); Sombra, A.S.(Universidade Federal do Ceará); dos Santos, L.P.(Universidade Federal do Ceará); de Vasconcelos, I.F.(Universidade Federal do Ceará);
Resumo:
Nanoparticles of various compositions have been the subject of intense scientific research due to their
unique properties and promising applications. Studies have focused on exploring these nanoparticles'
optical, magnetic, and catalytic properties, as well as their potential in biological and renewable energy
applications. In particular, crystals doped with rare earth elements have received special attention due to
their energy upconversion (UC) and downconversion (DC) properties. UC is a nonlinear optical process
in which at least two low-energy photons (near-infrared region) are converted into one high-energy
photon (visible region). On the other hand, DC is a process in which a high-energy photon (ultraviolet
region) is split into low-energy photons (visible region). In this study, nanocrystals of NaGdF4:Eu and
NaYF4:Gd,Eu, as well as NaGdF4:Yb,Er and NaGdF4:Yb,Tm, were prepared using co-precipitation with
ethylene glycol and lanthanide salts as precursors. NaGdF4:Eu3+ and NaYF4:Gd,Eu are examples of
DC luminescence materials exhibiting intense multicolored visible emissions under a single 395 nm light
excitation in the UV region. The emission spectrum recorded in the 575 to 700 nm spectral region
corresponds to 7F0 ? (5LJ + 5GJ) absorption transitions of Eu3+ ions. On the other hand,
NaGdF4:Yb,Er and NaGdF4:Yb,Tm are examples of UC luminescence materials. In these materials,
energy transfer from yttrium to erbium and thulium occurs when excited at 980 nm, corresponding to
Yb3+ absorption (transition 2F7/2 ? 2F5/2). In NaGdF4:Yb,Er, emissions are observed in the green (540
nm) and red (650 nm) regions of the electromagnetic spectrum due to the 4S3/2 ? 4I15/2 and 4F9/2 ?
4I15/2 transitions, respectively. In NaGdF4:Yb,Tm, emissions were detected in the blue (450 and 475
nm) and infrared (800 nm) regions of the electromagnetic spectrum due to the 1D2 ? 3F4, 1G4 ? 3H6,
and 3H4 ? 3H6 transitions. These materials were characterized using X-ray diffraction (XRD), UV-Vis
spectroscopy, photoluminescence, dynamic light scattering (DLS), and zeta potential.