Song Zeng-Fu

The Phase Transition Behavior of Mixtures of Nematic Liquid Crystal with Non-Mesogenic Solute Molecules

Abstract The magnetic birefringence and the refractive indices have been measured for the following binary solution systems: (1) Tetrabutyl-tin MBBA. (2) Cyclohexene MBBA. (3) Azobenzene MBBA. The reciprocal of Cotton-Mouton coefficients η and the order parameters S as a function of the temperature T for these systems have been calculated from this experimental data, The supercooling temperature T* and the order parameters at a given temperature decrease with increase of the mole fraction XB of solute. The slope of the η vs. T does not change for different concentrations and different kinds of solutes within our experimental accuracy.

Synthesis and characterization of some PSL phosphors

Abstract Some rare earth dopant photostimulated luminescence (PSL) phosphors (BaFBr:Eu 2+ , BaF 1.05 Br 0.95 :Eu 2+ , BaFCl:Eu 2+ , LaOBr:Tb and Ca 9 Ca-(PO 4 ) 6 Cl 2 :Eu 2+ ) have been synthesized. To evaluate whether these materials could be used for an image-storage plate for a computerized radiological system, we have specified and characterized some of their properties: PSL emission spectrum, stimulation spectrum, linearity of X-ray dose/PSL response, photostimulability, stability of the stored F-centres, dynamics of the PSL process, durability in long-run X-irradiation and stimulation, etc. These properties would affect the quality of image and the efficiency of the computerized system. They are also necessary parameters for the design of the optical, mechanical and electronic devices of the whole computerized radiological system.

Excited-State Upconversion of Pr(0.5)Yb(1.5):ZBLAN under Two-Colour Excitation

We report the excited-state upconversion in Pr(0.5)Yb(1.5):ZBLAN under two-colour excitation of 960 nm laser and xenon lamp light. Three obvious upconversion excitation peaks around 856.0, 804.2 and 787.1 nm were observed and the involved mechanism has been explained. The measured upconversion excitation peak 856.0 nm corresponds to the sum of theoretical values 852 nm and 866 nm owing to the 1G4(Pr3+)→ 1I6(Pr3+) and 1G4(Pr3+)→ 3P1(Pr3+) excited state absorption transitions. The measured 804.2 and 787.1 nm upconversion excitation peaks originate from the excited state absorption transitions 3H6(Pr3+)→ 1D2(Pr3+) and 1G4(Pr3+)→ 3P2(Pr3+), respectively. The excited state absorption upconversion 1G4(Pr3+)→ 1I6(Pr3+) is strong because of its large oscillator strength f = 23.040×10−6.

Comprehensive research about the cooperative up-conversion luminescence of the ytterbium- doped oxyfluoride vitroceramics

The cooperative up-conversion blue luminescence of Yb3+ ion-doped oxyfluoride vitroceramic material (Yb:FOV) and the influence of co-doped Ho3+ ion, when excited by a 960 nm diode-laser, are studied in this paper. A strong blue 479.1 nm up-conversion luminescence of the Yb:FOV material is discovered. It is found that the 479.1 nm luminescence results from the cooperative up-conversion of the coupled states of the Yb3+–Yb3+ clusters formed by two adjacent Yb3+ ions. The measured cooperative up-conversion luminescence main peak 479.1 nm of this paper is different from the characteristic fluorescence main peak of the Tb3+ ion positioned at about 495–504 nm wave-range. Our result coincides with all the published correct papers, whose cooperative up-conversion luminescence main peaks of the direct Yb3+–Yb3+ clusters are all positioned at about 476–480 nm wave-range. All of these indicate that the large cooperative up-conversion blue luminescence of the direct Yb3+–Yb3+ clusters discovered in this paper is stable. It further proves that the cooperative up-conversion green luminescence may result from the Yb3+-Tb3+ cooperative effect. In particular, the original work of this paper improves considerably on the traditional concept by the experimental facts that the blue 479.1 nm cooperative up-conversion luminescence strength of Yb(5):FOV is 230 times greater than that of fluoride glass Yb(3):ZBLAN. This is a great development to meet the practical requirements for blue up-conversion luminescence strength. This result indicates that the large cooperative up-conversion blue luminescence could be achieved excellently by using a suitable material, such as oxyfluoride vitroceramic, which provides a better chance to form better Yb3+–Yb3+ clusters and has less relaxation to keep the more efficient up-conversion luminescence. It is also found that impurities seriously reduce the cooperative up-conversion luminescence intensity due to the cross-relaxation from the Yb3+–Yb3+ clusters, which means that the cooperative up-conversion blue luminescence could be further improved by pure Yb3+ ion-doped materials that have as few impurities as possible to reduce the cross-relaxation. The large cooperative up-conversion blue luminescence of Yb(5):FOV also comes from its higher concentration (5 mol%) of activator Yb3+ ion which acts well because the cooperative up-conversion blue luminescence intensity varies linearly against the square of the concentration of Yb3+ ions in the range of 0.5–5 mol%. In summary, the great improvement of our work on cooperative up-conversion blue luminescence results from the comprehensive enhancement of the factors of better-coupled chance of the Yb3+–Yb3+ clusters, less cross-relaxation, better concentration contribution of Yb3+ activator, non-saturation and better up-conversion luminescence efficiency.

Non-resonant upconversion energy transfer of crystal ErP5O14

This paper reports the upconversion luminescence phenomenon of crystal ErP5O14 in ultraviolet to blue-green wave range induced by red DCM dye laser. The upconversion passage of each upconversion fluorescence is confirmed. It is found that the upconversion mechanism is mainly non-resonant upconversion energy transfers between rare earth ions when laser wavelength is near 650 nm. It is very interesting that the non-resonant upconversion energy transfer is achieved directly through a kind of coupling state of rare earth ion cluster and the ions do not exchange their phonon energy with crystal lattice.

Direct upconversion sensitization luminescence of Ho(0.1)Yb(5):oxyfluoride vitroceramics

This paper studies the upconversion luminescence phenomenon of the Ho,Yb co-doped oxyfluoride vitroceramics. There is one group of strong upconversion luminescence lines positioned at 536.5nm, 18639cm-1; 540.5nm, 18501cm-1; 544.0nm, 18399cm-1, which is easily identified as the transitions of 5S2 → 5I8. There are other splendid upconversion luminescence lines, which are 5S2 → 5I7, 5F5 → 5I8, 5G6 → 5I8, (5G3G)5 → 5I8, (3F3H5G)4 → 5I7, 5G4 → 5I8 and (5G3H)5 → 5I8. It is also found that an interesting kind of upconversion cooperative radiation fluorescence comes from a kind of coupling state of clusters consisting of two Yb3+ ions.