Enhancement of NIR emission varying thulium of ZrO2:2Yb3+-xTm3+ nanoparticles by sonochemical method

In this research, Yb3+ -Tm3+ co-doped ZrO2 nanoparticles (ZrO2:2Yb3+ -xTm3+; x=0.0125, 0.025, 0.05, 0.1, and 0.2 mol%) were synthesized using ethylenediamine and Pluronic F-127® as precipitating and surfactant agents, respectively, through a sonochemical method assisted by hydrothermal treatment and subsequent annealing as an innovative, simple, and fast route. Structural, morphological, and chemical characterization was determined by XRD, SEM, and FT-IR. The photoluminescent characterization was performed using a spectrometer with an excitation wavelength of 975 nm. The SEM technique confirms the formation of spherical and semispherical nanoparticles dispersed of sizes less than 110 nm. Furthermore, XRD results proved that the solids have monoclinic and tetragonal crystalline structure for undoped ZrO2 and the tetragonal phase was stabilized with Yb3+ -Tm3+ co-doped ZrO2. At the same time, FT-IR spectroscopy showed the functional groups corresponding to –OH residual, C-H, and C=C bonds due to surfactant agent remand and metallic oxide bonding of Zr-O, corresponding to the tetragonal crystal structure, principally. On the other hand, photoluminescent characterization exhibited upconversion (UC) emissions at 488, 656, and 800 nm due to 1G4→3H6, 1G4→3F4, and 3H4→3H6 transitions of Tm3+, respectively. These emissions increase in intensity due to the increment of Tm3+ concentration until 0.1mol%; lower and higher to this concentration, the photoluminescent intensity decrease. ZrO2:2Yb3+ -0.1Tm3+ nanoparticles showed the highest enhancement (144%) at 800 nm concerning the ZrO2:2Yb3+ -0.0125Tm3+ sample.