D. Solis

Role of Yb3+ and Er3+ concentration on the tunability of green-yellow-red upconversion emission of codoped ZrO2:Yb3+–Er3+ nanocrystals

Strong green and red visible emissions were obtained from ZrO2:Yb3+–Er3+ nanocrystals synthesized by sol-gel method and annealed at 1000 °C for 5 h. The average crystallite size was ∼70 nm with tetragonal phase for total concentration lower than 3 mol % and cubic phase for concentration higher than 5 mol %. The color coordinate of the upconverted signal was tailored by controlling the dopant composition that change the red/green ratio dominated by the cross relaxation and energy back transfer process as was demonstrated theoretically and confirmed experimentally. Both coefficients were calculated, C51∼1.02×10−16 and C5b∼6.04×10−17, from the theoretical model based on the rate equations. The highest energy transfer efficiency was η∼64% for 2 mol % of Yb and 2 mol % of Er3+. However, for the highest upconverted signal was only η∼29% obtained for 2 mol % Yb and 1 mol % Er with effective decay time τeff∼438 μs for red and τeff∼290 μs for green band.

Influence of surface coating on the upconversion emission properties of LaPO4:Yb/Tm core-shell nanorods

A solution based hydrothermal method is used for the preparation of LaPO4:Yb–Tm doped and LaPO4:Yb/Tm core-shell upconverted nanorods. The morphologies, structure, formation mechanism, and upconversion emission properties of these nanocrystals are investigated in detail. Tensile strain is observed for LaPO4:Yb–Tm doped material but compressive strain is obtained for LaPO4:Yb/Tm core-shell material. Analysis suggests that the lattice strain plays an important role on the upconversion emission. Bright blue (475 nm) and red (650 nm) upconversion emissions associated to G14→H36 and F32→H36 transitions were observed and a significant higher in upconversion emission intensity is observed in core-shell nanorods. The effective decay time calculated are 230 and 110 μs for core-shell and doped nanorods, respectively, indicating the removal of surface defects due to surface coating. It reveals that the core-shell structure shows better upconversion emission efficiency.

Blue-green upconversion emission in ZrO2:Yb3+ nanocrystals

Strong blue-green cooperative upconversion emission was observed under infrared excitation in 70 nm average crystallite size ZrO2:Yb3+ nanocrystals prepared by sol-gel process. The structural characterization was performed by x-ray diffraction and high resolution transmission electron microscopy suggesting that crystalline phase of nanoparticles is controlled by active ion concentration. The cooperative absorption coefficient η∼2.5×10−22 is four orders of magnitude larger than the ones reported from bulk crystals. The highest emission intensity was obtained from the doped sample at 4 mol % and was the result of the simultaneous relaxation of two excited Yb ions. Decay time of the upconverted signal τCUC≈0.310 ms is half from the near infrared effective decay time confirming the cooperative process among Yb ions. Such strong cooperative effect is explained in terms of interaction enhancement due to the diminishing of Yb–Yb separation promoted partly by the surface recombination of nanocrystals.

Green upconverted emission enhancement of ZrO2 : Yb3+–Ho3+ nanocrystals

ZrO2 : Yb3+–Ho3+ nanocrystals with different concentrations of codopants were synthesized with a 0.0082 molar ratio of surfactant Pluronic F-127 using a sol–gel micelle method, and annealed at 1000 °C for 5 h. The dominant crystallite phase was tetragonal, with an average crystallite size of 20 nm. The upconverted signal produced by the codoped nanocrystals is an almost pure green emission centred at 540 nm caused by the radiation emitted by the 5F4 + 5S2 → 5I8 relaxation of Ho3+. The highest efficiency for the Ho3+ green emission, with a decay constant (τeff) of 360 µs, was obtained with a 2/0.001 mol% Yb/Ho composition. This yields a colour coordinate of (0.289, 0.699) with a maximum luminance of 8.7 × 10−3 lm after excitation with a 970 nm continuous wave laser diode. These results can be explained in terms of the energy transfer (ET) from the donor (Yb3+) to the acceptor (Ho3+). The ET efficiency (η) for this sample was only 5%, although an increase to 42% is possible for larger concentrations of Ho3+. Highly concentrated samples have shortened decay times, which cause highly saturated samples to exhibit larger ET efficiency values.

Cooperative Pair Driven Quenching of Yb3+ Emission in Nanocrystalline ZrO2:Yb3+

The concentration luminescence quenching of the NIR emission of Yb3+ in nanocrystalline ZrO2 is studied. It is found that the quenching is dominated by cooperative energy transfer processes from isolated Yb3+ ions to Yb-Yb pairs (Yb dimers). The Yb dimer concentration depends on the crystallite phase and size, which on time depends on Yb concentration. An extended energy transfer model was developed to predict the IR and cooperative visible fluorescence emissions by taking in to account the crystalline phase, the nanocrystals size, and the geometrical construction of Yb dimers. Our model succeeds to fit simultaneously both experimental VIS and NIR emissions, and the corresponding interaction parameters are reported.

Synthesis and characterization of upconversion emission on lanthanides doped ZrO 2 nanocrystals coated with SiO 2 for biological applications

Er doped and Yb-Er-Tm codoped ZrO2 nanocrystals of average 80 nm in size were prepared by a sol-gel process with the presence of nonionic (PLURONIC F-127) surfactant, and the up-conversion emission was characterized under IR (980 nm) excitation. The effect of the codoped conditions on the crystalline structure and photoluminescence properties were studied. A strong green emission was produced with 5 mol %, 0.2 mol %, 0.01 mol % of Yb3+-Er3+-Tm3+ codoped ZrO2 respectively. It was prepared Er doped ZrO2 -SiO2 core-shell and SiO2 coated Er doped ZrO2 in 2-propanol and water, respectively. The presence of the silica shell of average of 15 nm in thickness has been confirmed by transmition electron microscopy. Photolumineiscence studies show that the silica shell does not affect the emission when the nanoparticles are excited with 980 nm. The up-converting Yb3+-Er3+-Tm3+ codoped ZrO2 nanocrystal has showed to be a powerful tool to future detection techniques. The viability of the nanoparticles of codoped ZrO2 for biological imaging was confirmed by multiphotonic microscope imaging of cervix tissue with inserted codoped ZrO2 nanoparticles. The cervix tissue has a moderate dysplasia. The nanoparticles were introduced at 80 % of the tissue depth (5 μm) without being functionalized.

Synthesis and characterization of upconversion emission on lanthanides doped ZrO[sub]2[/sub] nanocrystals coated with SiO[sub]2[/sub] for biological applications

Er doped and Yb-Er-Tm codoped ZrO2 nanocrystals of average 80 nm in size were prepared by a sol-gel process with the presence of nonionic (PLURONIC F-127) surfactant, and the up-conversion emission was characterized under IR (980 nm) excitation. The effect of the codoped conditions on the crystalline structure and photoluminescence properties were studied. A strong green emission was produced with 5 mol %, 0.2 mol %, 0.01 mol % of Yb3+-Er3+-Tm3+ codoped ZrO2 respectively. It was prepared Er doped ZrO2 -SiO2 core-shell and SiO2 coated Er doped ZrO2 in 2-propanol and water, respectively. The presence of the silica shell of average of 15 nm in thickness has been confirmed by transmition electron microscopy. Photolumineiscence studies show that the silica shell does not affect the emission when the nanoparticles are excited with 980 nm. The up-converting Yb3+-Er3+-Tm3+ codoped ZrO2 nanocrystal has showed to be a powerful tool to future detection techniques. The viability of the nanoparticles of codoped ZrO2 for biological imaging was confirmed by multiphotonic microscope imaging of cervix tissue with inserted codoped ZrO2 nanoparticles. The cervix tissue has a moderate dysplasia. The nanoparticles were introduced at 80 % of the tissue depth (5 μm) without being functionalized.

Synthesis and characterization of upconversion emission on lanthanides doped ZrO2 nanocrystals coated with SiO2 for biological applications

Er doped and Yb-Er-Tm codoped ZrO2 nanocrystals of average 80 nm in size were prepared by a sol-gel process with the presence of nonionic (PLURONIC F-127) surfactant, and the up-conversion emission was characterized under IR (980 nm) excitation. The effect of the codoped conditions on the crystalline structure and photoluminescence properties were studied. A strong green emission was produced with 5 mol %, 0.2 mol %, 0.01 mol % of Yb3+-Er3+-Tm3+ codoped ZrO2 respectively. It was prepared Er doped ZrO2 -SiO2 core-shell and SiO2 coated Er doped ZrO2 in 2-propanol and water, respectively. The presence of the silica shell of average of 15 nm in thickness has been confirmed by transmition electron microscopy. Photolumineiscence studies show that the silica shell does not affect the emission when the nanoparticles are excited with 980 nm. The up-converting Yb3+-Er3+-Tm3+ codoped ZrO2 nanocrystal has showed to be a powerful tool to future detection techniques. The viability of the nanoparticles of codoped ZrO2 for biological imaging was confirmed by multiphotonic microscope imaging of cervix tissue with inserted codoped ZrO2 nanoparticles. The cervix tissue has a moderate dysplasia. The nanoparticles were introduced at 80 % of the tissue depth (5 μm) without being functionalized.