RESUMO
In the present paper, the collapsing dynamics of a laser-induced cavitation bubble near the edge of a rigid wall is experimentally investigated with a high-speed photography system. For a symmetrical setup, the two primary control parameters of the bubble collapsing behavior include the equivalent maximum bubble radius and the distance between the bubble and the edge of the rigid wall. Based on the bubble interface deformation during the collapsing process, three typical cases are identified for the categorization of the phenomenon with the influences of the parameters revealed. Through a quantitative analysis of the obtained high-speed photos, the motions of the bubble interface in different directions are given together with the calculations of the bubble centroid. The primary findings of the present paper could be summarized in terms of the bubble-edge distance as follows. When the bubble is close to the edge, the movement of the bubble interface near the edge will be restricted with a clear neck formation in the middle part of the bubble. For this case, the edge could delay the bubble collapsing time up to 22% of the Rayleigh collapsing time. When the bubble is of the medium distance to the edge, the differences of the expansion or shrinkage of the bubble interface among different directions will be reduced with an olive-shaped bubble formed during the collapsing process. For this range of parameters, the bubble moves rapidly toward the edge especially during the final collapsing stage. When the bubble is far away from the edge, the bubble will be a nearly spherical one.
RESUMO
In this Reply, we truthfully respond to the comments on our recent paper entitled "A universal approach for calculating the Judd-Ofelt parameters of RE3+ in powdered phosphors and its application for the ß-NaYF4:Er3+/Yb3+ phosphor derived from auto-combustion-assisted fluoridation" published in Phys. Chem. Chem. Phys. [Y. Zhang, B. Chen, S. Xu, X. Li, J. Zhang, J. Sun, X. Zhang, H. Xia, R. Hua, A universal approach for calculating the Judd-Ofelt parameters of RE3+ in powdered phosphors and its application for the beta-NaYF4:Er3+/Yb3+ phosphor derived from auto-combustion-assisted fluoridation, Phys. Chem. Chem. Phys., 20, 2018, 15876-15883]. In the Comment, the authors oppugned partial calculation results we reported in our original paper, thus we redid the calculations and compared the presently obtained results with the original ones and the author provided ones. The recalculations and comparisons confirmed that our calculations are reproducible and the results are correct. In the Comment, the authors also made some comments on the Judd-Ofelt calculation approaches for powdered samples reported by other researchers. Following the authors' train of thought we added some supplements to the comments to understand the application strategy of Judd-Ofelt theory. Furthermore, we extended some points of view regarding the fluorescence lifetime measurements the authors presented in the Comment.
RESUMO
It is difficult to calculate the Judd-Ofelt (J-O) parameters for trivalent rare earth (RE)-doped powders due to the unavailable absorption spectrum that is necessarily used in the conventional J-O calculation procedure. In this study, a universal method starting from the diffuse-reflection spectrum for calculating the J-O parameters of RE3+-doped powdered samples was proposed. In this proposed method, by taking the Kubelka-Munk function into account, the absorption cross-section spectrum was derived from the diffuse-reflection spectrum in the RE3+-doped powdered sample using the connection between the absorption cross section and the radiative transition rate of RE3+. Then, the J-O parameters might be calculated from the absorption cross-section spectrum via the traditional J-O calculation technique. The NaYF4:Er3+/Yb3+ and NaYF4:Er3+ phosphors were prepared via an auto-combustion-assisted fluoridation technique, and the J-O calculation was carried out for the obtained samples. The obtained J-O parameters were compared with those reported in the literature and also verified by comparing the calculated radiative transition lifetimes with the experimental values. Finally, it was deduced that the proposed J-O calculation route was practicable.
RESUMO
A core-shell structure with a NaYF4:Sm3+/Yb3+ core for photothermal conversion nanocalorifier and a NaYF4:Er3+/Yb3+ shell as temperature probe for potential applications in photothermal therapy (PTT) were synthesized by a thermal decomposition technique of rare-earth oleate complexes. The optical temperature reading-out property for the NaYF4:Sm3+/Yb3+@NaYF4:Er3+/Yb3+ core-shell structure was systematically investigated and it was found that in comparison with pure NaYF4:Er3+/Yb3+ particles, the temperature sensing performance of the NaYF4:Er3+/Yb3+ shell did not become worse due to the presence of NaYF4:Sm3+/Yb3+ core. Furthermore, the photothermal conversion behavior for core-shell nanoparticles was successfully examined by dint of temperature sensing of the NaYF4:Er3+/Yb3+ shell, and it was found that an excitation-power-density-dependent temperature increase of up to several tens degrees can be achieved. All the experimental results suggested that the core-shell structure may be an excellent nanocalorifier candidate for advanced temperature-controllable PTT.
RESUMO
Tm³âº/Yb³âº codoped NaY(WO4)2 microstructures with various Tm³âº concentrations and 10 mol% Yb³âº concentration were prepared by a microwave-assisted hydrothermal method, and their upconversion luminescence (UCL) was investigated. Under excitation at 980 nm, Tm³âº/Yb³âº codoped NaY(WO4)2 exhibited strong blue and near infrared (NIR) emissions, respectively, corresponding to ¹G4 --> ³H6 and ³H4 --> ³H6 transitions, with weak red emission due to the ¹G4 --> ³H4 transition. The optimum doping concentrations of Tm³âº for the highest blue and NIR UCL were investigated, and it was found that the optimal concentrations for blue and NIR emissions were 0.5 mol% and 1.5 mol%, respectively. In addition, an analysis of temperature dependent blue and NIR UCL in both the samples with low and high Tm³âº concentrations, respectively, was undertaken. The results implied that the sample with low Tm³âº concentration displayed more obvious effect on the thermal quenching of ¹G4 level.
RESUMO
Er3+/Yb3+ co-doped nanocrystal Y2O3 powders with different sizes were prepared by using a chemical auto-combustion reaction. X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) were used to characterize the crystal structure and morphology of the samples. Fourier transform infrared (FT-IR) spectra showed that the surfaces of smaller particles absorbed a larger amount of NO3-, CO3(2-) and OH- groups. These chemical groups caused an increase of the population ratios of the 4I13/2 level to the 4I11/2 level when the particle size decreased, thus resulting in a change of the red-green upconversion emission intensity ratio under 980 nm excitation. The 1.5 microm emission intensity also changed with the particle size. These results suggest that surface status is an important factor influencing the luminescent properties of nano-sized materials and that surface modification is needed in order to obtain the satisfied materials.
