[en] Several interesting quantum liquid systems are studied theoretically. The method to approach each system is chosen by considering the special properties of that system. First principles variational theory is developed to study the properties of the ground state of many-electron atomic systems. The inhomogeneity and strong Coulomb interaction are taken into account directly. The correlation energies calculated are in good agreement with experimental data. Particle-field interactions reveal another aspect of quantum liquids. The system with positive ions embedded in superfluid ⁴He is used as an example to study particle-field interactions in quantum liquids. A quantum model is proposed and solved by a variational method. The quantum Hall effect is one of the most important discoveries in condensed matter systems. From a quantum scattering theory, the quantum Hall effect in quasi-three-dimensional systems observed in semiconductor superlattices is explained and general criteria for the quantum Hall effect in such systems are given. Superconducting-insulating phase transition in ultrathin films realizes many aspects of the theory of localization and quantum fluctuation. A simple analysis for the superconducting-insulating phase transition in ultrathin films indicates the phase transition is a combined effect of pairing and localization

[en] Upconversion luminescent nano-materials with both excitation and emission peaks in the "optical window" is of significant importance for application in deeper bio-imaging, due to the weak effects of light absorption, light scattering, and auto-fluorescence. This paper reports an Er${}^{3+}$ self-sensitized red up-converting nanophosphors with improved emission intensity and spectral purity. The influence of Yb${}^{3+}$ concentration on upconversion luminescence properties is investigated comprehensively. Compared with the sample without Yb${}^{3+}$ doping, the luminescence intensity in the sample with 10% Yb${}^{3+}$ is increased by 12.9 times. Moreover, the dominant wavelength at 1550 nm excitation is about 60 nm larger than that excited at 980 nm. It has been demonstrated that Yb${}^{3+}$ co-doping can not only improve the photon absorption at 1550 nm and the probability of red emission, but also suppress other light emissions and phonon emission through the selective population of red-emitting level.

[en] CaSnO_3:Yb"3"+, Er"3"+, Li"+ upconverting phosphors are synthesized by a simple solid state method. The doping concentration of Li"+ ions is optimized by comparatively studying upconversion luminescence of samples with various Li"+ content. The effects of Yb"3"+ concentration, pumping power and temperature on chromaticity of upconversion luminescence in CaSnO_3:Yb"3"+, Er"3"+, Li"+ phosphors are investigated, the related mechanisms are discussed and the abilities to modulate chromaticity are evaluated.

[en] High luminescence intensity is crucial for realizing luminescent temperature sensing with a large signal-to-noise ratio. In this work, the temperature sensing behavior of Ca_1-xNa_xMoO₄:Yb³⁺,Er³⁺ with intense green up-conversion luminescence was studied. It has been demonstrated that the single-band green emission was dependent on the Yb³⁺-MoO₄^2- dimer sensitization as well as the low multi-phonon relaxation rate of ⁴S_3/2 → ⁴F_9/2. In addition, it was found that the uncorrected thermometer could not accurately measure temperature due to thermal effects. A simple method for calibration of up-conversion temperature sensing was reported. Due to high luminescence intensity and temperature sensitivity, Ca_1-xNa_xMoO₄:Yb³⁺,Er³⁺ is a promising candidate for up-conversion temperature sensing.

[en] A mixture of two types of hard-sphere bosons in a disk-shaped harmonic trap is studied through path-integral quantum Monte Carlo simulation at low temperature. We find that the system can undergo a phase transition to break the spatial symmetry of the model Hamiltonian when some of the model parameters are varied. The nature of such a phase transition is analyzed through the particle distributions and angular correlation functions. Comparisons are made between our calculations and the available mean-field results on similar models. Possible future experiments are suggested to verify our findings

[en] Based on the study of improving the stress corrosion resistance of 5A03 aluminum alloy for ship, this paper mainly studied the tensile test, surface morphology and residual stress under laser shock, high temperature and stress corrosion. It is found that the residual compressive stress and the grain refinement on the surface of the material during the heat strengthening process increase the breaking strength of the sample in the stress corrosion environment. Appropriate high temperature maintenance helps to enhance the effect of deformation strengthening. In the 300°C environment insulation, due to recrystallization of the material, the performance decreased significantly. This study provides an experimental basis for effectively improving the stress corrosion resistance of 5A03 aluminum alloy. (paper)

[en] Highlights: • A method for evaluating the reliability of temperature measurement standards is reported. • Influence of thermal effect on upconversion luminescent temperature sensing is investigated. • A reliable temperature scale based on intense green upconversion emissions of Y2Mo4O15:Yb³⁺/Er³⁺ is established. - Abstract: In this paper, Y₂Mo₄O₁₅:Yb³⁺/Er³⁺ upconversion phosphors are prepared by a co-precipitation method. In the case of 20% Yb³⁺ doping, the intense green upconversion luminescence is obtained, which can be attributed to the energy transfer from Yb³⁺-MoO₄^2- dimer to Er³⁺ that suppresses the multi-phonon relaxation of ⁴I_11/2 to ⁴I_13/2. Similar the Yb³⁺ sensitization, the dimer sensitization is also dependent on the Yb³⁺ concentration. When the Yb³⁺ concentration exceeds 20%, the luminescence is quenched by the cross relaxation and energy migration between dimers. A method for evaluating the reliability of temperature measurement standards is reported. Moreover, in term of the reliable temperature scale, the maximum absolute sensitivity of sample doped with 20% Yb³⁺ is determined to be 0.0117 K^-1. Favorable sensing ability and strong upconversion luminescence indicate that the optimum sample is potentially applicable as the optical thermometric materials.

[en] The hexagonal NaGdF₄:Yb³⁺/Ho³⁺/Ce³⁺ nano-phosphors are synthesized by a hydrothermal method. Under 980 nm excitation, the phosphor emits green, red and far-red light in the visible wavelength region, corresponding to the ⁵S₂/⁵F₄ → ⁵I₈, ⁵F₅ → ⁵I₈ and ⁵S₂/⁵F₄ → ⁵I₇ transitions of Ho³⁺ ions, respectively. When adjusting the Ce³⁺ concentration from 0% to 16%, the dominant wavelength shifts ∼43 nm toward the longer wavelength. Two cross-relaxation processes between Ho³⁺ and Ce³⁺ are responsible for the change in chromaticity. Also, the ability of the Ce³⁺ concentration to regulate the luminescence color depends on the pumping power and temperature of samples. More interestingly, the phosphors are potentially applicable as the optical thermometric materials. In the case of 16% Ce³⁺ doping, the maximum sensitivity (0.1446 K⁻¹) about 4–35 times as high as the reported values of several typical thermometric materials is obtained. (paper)

[en] Upconversion luminescence of Yb³⁺/Er³⁺ and Yb³⁺/Tm³⁺ co-doped Y₂(MoO₄)₃ phosphors under 980 nm excitation is investigated. It is demonstrated that Yb³⁺ co-doping causes a significant thermal effect. For Yb³⁺ and Er³⁺ co-doped case, the thermal effect, the long-distance energy migration and the energy transfer from Er³⁺ to Yb³⁺ are responsible for the abnormal luminescence quenching. In the case of Yb³⁺ and Tm³⁺ co-doped, the thermal effect improves the excited efficiency of Tm³⁺, and thus the luminescence of Tm³⁺ continues to strengthen at the Yb³⁺ concentration that causes Er³⁺ luminescence quenching. These results contribute to the design of the efficient upconversion materials. (paper)

[en] In this paper, a novel upconversion phosphor is reported. Based on XRD and EDS, it is confirmed that the phosphor is monoclinic Gd₂Mo₄O₁₅:Yb³⁺, Ho³⁺ with P21/c space group. The non-radiation decay of ⁵I₆ to ⁵I₇ dominants the depopulation of ⁵I₆, thus the phosphor produces the red upconversion emission with high emission intensity and good color quality, and shows the favorable temperature sensing property. When using non-continuous excitation mode, the temperature sensitivity is determined as 0.0452 K⁻¹. Because the sensitivity is the same at any temperature, the new upconversion material may have greater potential for temperature sensing application than Er³⁺ doped upconverison materials. (paper)