Synthesis of Yb3+/Er3+ co-dopants sodium yttrium fluoride up-conversion fluorescence materials

Up-conversion Persistent Luminescence of a 980 nm Laser Activated Zn3Ga2(GexSn1-x)O8:Yb,Er,Cr Phosphors

Zn₃Ga₂(Ge_xSn_1-x)O₈:Yb,Er,Cr phosphors with different doping ratio of Ge/Sn were prepared by high temperature solid-state method. After excited at 270 nm with a xenon lamp for 15 min, the persistent luminescence (PL) of Zn₃Ga₂(Ge_xSn_1-x)O₈:Yb,Er,Cr phosphor can last more than 60 min. Under the excitation at 980 nm, Zn₃Ga₂(Ge_xSn_1-x)O₈:Yb,Er,Cr phosphors can generate effective up-conversion emissions from Er³⁺ ions at 410 nm, 525 nm, 550 nm, 660 nm and Cr³⁺ ions around 700 nm. Besides, after ceasing irradiation, Zn₃Ga₂(Ge_xSn_1-x)O₈:Yb,Er,Cr phosphors show up-conversion persistent luminescence (UCPL) from Cr³⁺ ions around 700 nm. Moreover, Zn₃Ga_1.995(Ge_0.3Sn_0.7) O₈:Yb³⁺,Er³⁺,Cr³⁺ phosphor is optimal with the best persistent luminescent and up-conversion persistent luminescent properties. In short, owing to the long afterglow time, strong up-conversion emissions and novel up-conversion persistent luminescence, the as-prepared Zn₃Ga₂(Ge_xSn_1-x)O₈:Yb,Er,Cr phosphors can be potentially applied in a wide range of fields, such as security materials, coating materials, infrared detection, fluorescent label, tracer and testing.

Tunable multicolor and white-light upconversion luminescence in Yb3+/Tm3+/Ho3+ tri-doped NaYF4 micro-crystals

NaYF4 micro-crystals with various concentrations of Yb(3+) /Tm(3+) /Ho(3+) were prepared successfully via a simple and reproducible hydrothermal route using EDTA as the chelating agent. Their phase structure and surface morphology were studied using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns revealed that all the samples were pure hexagonal phase NaYF4. SEM images showed that Yb(3+)/Tm(3+)/Ho(3+) tri-doped NaYF4 were hexagonal micro-prisms. Upconversion photoluminescence spectra of Yb(3+)/Tm(3+)/Ho(3+) tri-doped NaYF4 micro-crystals with various dopant concentrations under 980 nm excitation with a 665 mW pump power were studied. Tunable multicolor (purple, purplish blue, yellowish green, green) and white light were achieved by simply adjusting the Ho(3+) concentration in 20%Yb(3+)/1%Tm(3+)/xHo(3+) tri-doped NaYF4 micro-crystals. Furthermore, white-light emissions could be obtained using different pump powers in 20%Yb(3+)/1%Tm(3+)/1%Ho(3+) tri-doped NaYF4 micro-crystals at 980 nm excitation. The pump power-dependent intensity relationship was studied and relevant energy transfer processes were discussed in detail. The results suggest that Yb(3+)/Tm(3+) Ho(3+) tri-doped NaYF4 micro-crystals have potential applications in optoelectronic devices such as photovoltaic, plasma display panel and white-light-emitting diodes.

Colloidal synthesis and blue based multicolor upconversion emissions of size and composition controlled monodisperse hexagonal NaYF4:Yb,Tm nanocrystals

Monodisperse beta-NaYF4:Yb,Tm nanocrystals with controlled size (25-150 nm), shape (sphere, hexagonal prism, and hexagonal plate), and composition (Yb: 20-40%, Tm: 0.2-5%) were synthesized from the thermolysis of metal trifluoroacetates in hot surfactant solutions. The upconversion (UC) of near-infrared light (980 nm) to ultra-violet (360 nm), blue (450 and 475 nm), red (650 and 695 nm) and infrared (800 nm) light in the beta-NaYF4:Yb,Tm nanocrystals has been studied by UC spectroscopy. Both the total intensity of UC emissions and the relative intensities of emissions at different wavelengths have shown a strong dependence on different particle sizes and different Tm3+ and Yb3+ concentrations. As a result, different overall output colors of UC emissions can be achieved by altering sizes and Yb3+/Tm3+ doping concentrations of the beta-NaYF4:Yb,Tm nanocrystals. The intensity-power curves of a series of samples have proved that emissions at 360 and 450 nm can be ascribed to four-photon process (1D2 to 3H6 and 1D2 to 3H4, respectively), while emissions at 475 and 650 nm are three-photon processes (1G4 to 3H6 and 1G4 to 3H4, respectively) and emissions at 695 and 800 nm are two-photon ones (3F2 to 3H6 and 3F4 to 3H6, respectively). A UC saturation effect would occur under a certain excitation intensity of the 980 nm CW diode laser for the as-obtained beta-NaYF4:Yb,Tm nanocrystals, leading to the decrease of the slopes of the I-P curves. The results of our study also revealed that the successive transfer model instead of the cooperative sensitization model can be applied to explain the UC behaviors of the beta-NaYF4:Yb,Tm nanocrystals. Further, an unexpected stronger emissions of four-photon process at 360 and 450 nm for approximately 50 nm beta-NaYF4:Yb,Tm nanocrystals than those for the bigger (approximately 150 nm) nanocrystals was observed and explained in terms of the effects of crystallite size, surface-to-volume ratio and homogeneity of the doping cations.