Upconversion And Downconversion Properties Of Rare Earths Co-doped TeO₂Nanoparticles

The rare earth doped luminescent materials are excellent optical materials withhigh photochemical stability, sharp emission bandwidths, large anti-stokes shift,remarkable light penetration depth and the absence of background fluorescence.Nowadays, They have been applied in many fields. Especially, upconversionluminescent materials are very promising for biological and medical investigations. Inthis study, TeO₂nanoparticles were used as the host materials to prepare rare earthions co-doped upconversion luminescent materials.TeO₂:Er³⁺/Yb³⁺nanoparticles had been prepared via a hydrothermal process. Themorphology and crystallization was characterized by Transmission electronmicroscopy （TEM） and X-ray diffraction （XRD） technique, respectively. Theupconversion emission spectra and upconversion mechanisms had been alsoinvestigated. The as-prepared sample showed the green emissions （525nm,545nm）and red emission （667nm） under980nm excitation. The rare earth ions dopingconcentration was optimized. The slopes value for blue, green and red emissions wascalculated. The result indicated that the emission intensities of the α-TeO₂:Er³⁺/Yb3+nanoparticles and β-TeO₂: Er³⁺/Yb³⁺nanoparticles were much stronger than those ofthe （α+β）-TeO₂:Er³⁺/Yb³⁺nanoparticles.α（β）-TeO₂:Tm³⁺/Er³⁺/Yb³⁺nanoparticles had been characterized by Transmissionelectron microscopy （TEM） and X-ray diffraction （XRD） technique, respectively. Theupconversion emission spectra and upconversion mechanisms had been alsoinvestigated. All the samples showed the blue （476nm）, green （525nm,545nm）and red （667nm） emissions under980nm excitation. The calculated CIE colorcoordinates of samples changed with the concertration of Yb3+ions. The combinationof blue, green and red emissions resulted in the white luminescence which was intenseand visible to the naked eyes. The calculated CIE color coordinates ofTeO₂:Tm³⁺/Er³⁺/Yb³⁺nanoparticles fell well within the white region and changed littlewith the incident pump power. A further study was conducted on upconversionemission enhancement in TeO₂:Tm³⁺/Er³⁺/Yb³⁺/Li+nanoparticles by incorporation ofLi+ions. The result indicated that the emission intensities of theTeO₂:Tm³⁺/Er³⁺/Yb³⁺/Li⁺nanoparticles were much stronger than those sampleswithout Li+ions. The emission intensities increased with the concertration of Li⁺ions.The preparation and downconversion emission property of TeO₂:Eu³⁺nanoparticles was also studied. The excitation and emission spectra indicated that itcould be efficiently excited at395nm or466nm and the strongest emission peaks wereat592nm and615nm. The luminescence intensities changed with the different Eu3⁺concentrations.