RESUMEN
As for tetrahedron-based ultraviolet nonlinear optical crystals, it is so difficult to achieve a sufficient birefringence to satisfy the phase-matching condition. Thereover, it is necessary to greatly increase the polarizability anisotropy of tetrahedra. Meanwhile, the tetrahedra should be arranged as uniformly as possible. Based on these ideas, a new strategy that dimerizes the heteroleptic tetrahedra with heteroleptic atoms as bridges is proposed and implemented, resulting in a new compound, Na2 S3 O6 , which crystallizes in a centrosymmetric monoclinic phase (phase-I) and a non-centrosymmetric orthorhombic one (phase-II). In the phase-I, a large birefringence of 0.103 @ 546 nm comparable to those of many triangle-based crystals is confirmed experimentally, indicating the ability of [S3 O6 ] group in improving the birefringence. Besides, the phase-II exhibits an improved birefringence of 0.056 @ 546 nm and a moderate second harmonic generation response of 1.4 × KH2 PO4 . In particular, the phase-II exhibits a typical phase-matching behavior under the irradiation of 532 nm laser. Moreover, the excellent optical properties of [S3 O6 ] group are further verified by theoretical calculations. These results completely illustrate the validity of the design strategy. Therefore, this work lights a new route for exploring novel ultraviolet nonlinear optical crystals.
RESUMEN
The application of digital imaging to color measurement is more and more extensive, which also provides new ideas for gemology. In this paper, the single-factor experiment method and orthogonal experiment design are used to study the influence parameters of the digital imaging system (DIS) on gem color measurement. Among them, the illuminance has the most significant impact on the measurement results, followed by the exposure time, and the change of the measurement distance has an insignificant impact on the results; through range analysis and analysis of variance, the most suitable measurement parameters for red jadeite are 1600 lx, 12,500 µs, 25 cm.
RESUMEN
The chemical composition and influencing factors of the colour of 95 yellow to light blue iron-bearing beryl are studied through Electron Microprobe Analysis (EMPA), Energy-dispersive X-ray fluorescence (ED-XRF) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy and X-Rite SP62 spectrophotometer. The intensities of the three characteristic hydroxyl stretching bands of the beryl from 3500 cm-1 to 3800 cm-1 prove they are low to medium levels of alkali bearing natural beryl. The wide absorption edge of 320 ~ 465 nm caused by the ultra-violet charge transfer from O2- to Fe3+ and the 650 nm absorption band in E//c-polarization caused by the intervalence charge transfer between Fe2+ and Fe3+ are the main factors affecting the colour of beryl. By applying CIE D65 standard light source and N9 Munsell neutral background as testing conditions, the colour parameters of 82 gem-quality beryl are tested. According to the results, iron-containing beryl colours are classified into yellow, yellowish-green, bluish-green, greenish-blue, and blue by the K-means cluster analysis method. The blue tone has a greater influence on the hue of beryl, while the yellow tone has a greater influence on the chroma. Iron content is higher in yellow and blue beryl. With the increase of iron content, the lightness of beryl decreased and the chroma increased.