Near infrared and charge transfer luminescence of Yb-doped LaPO4 at room temperature

The Yb³⁺-doped LaPO₄ was prepared by hydrothermal reaction under fine acidity control and identified by X-ray diffraction and FT-IR spectroscopy. The obtained powders crystallize in the monoclinic phase of LaPO₄. The spectroscopic study at room temperature (RT) of the Yb³⁺-doped LaPO₄ powder was investigated. Thus a wide band, characteristic of the fundamental ²F_5/2↔²F_7/2 transition in near infrared (NIR) range, has been located for La_(1−x)Yb_xPO₄ (x = 5, 10%). Four Stark levels of the ground ²F_7/2 state are located on the emission spectra between 976 nm and 1030 nm, after excitation at 925 nm. Low re-absorption of the 0-phonon transition was registered. Charge transfer band (CTB) luminescence of Yb³⁺, which is not observed in LaPO₄ in later works, was appeared under 266 nm excitation. In the UV–Visible spectra, double band typical for the CTB luminescence of Yb³⁺ are observed. The decay time dependence as a function of the concentration is also reported and compared to other works. The room temperature radiative lifetimes of the IR emission and charge transfer band luminescence are compatible with potential applications of this phosphor respectively as solid-state lasers and scintillators.     

介质pH对银基上4-甲基-4H-3-巯基-1,2,4-三氮唑成膜结构和缓蚀性能影响的SERS和电化学研究

在不同pH介质中,缓蚀试剂4-甲基-4H-3-巯基-1,2,4-三氮唑(4-MTTL)都能在银基底上形成自组装膜。SERS光谱表明:当pH=3时,4-MTTL分子是以硫醇式,通过两个氮原子为吸附位点,以较平躺方式在银表面构筑自组装膜;当介质为pH=7和pH=11时,4-MTTL以硫醇式,通过氮和硫原子为吸附位点倾斜或垂直方式作用于银表面。由于后者的吸附方式比前者更为垂直于表面,所以形成的膜中分子排列更为致密。电化学极化实验也表明,在pH=3的条件下,形成的4-MTTL单层有更正的腐蚀电位;在pH=11时,构筑的膜缓蚀能力强于pH=7的。并由电化学交流阻抗数据解析了相应的缓蚀机理。     

Surface‐enhanced Raman spectroscopy of 4‐tert‐butylpyridine on a silver electrode

We report the observation of large surface‐enhanced Raman scattering (SERS) (10⁶) for 4‐tert‐butylpyridine molecules adsorbed on a silver electrode surface in an electrochemical cell with electrode potential set at − 0.5 V. A decrease in electrode potential to − 0.3 V was accompanied by a decrease in relative intensities of the vibrational modes. However, there were no changes in vibrational wavenumbers. Comparison of both normal solution Raman and SERS spectra shows very large enhancement of the intensities of a₁, a₂, and b₂ modes at laser excitation of 488 nm. Enhancement of the non‐totally symmetric modes indicates the presence of charge transfer as a contributor to the enhancement. Copyright © 2011 John Wiley & Sons, Ltd.     

Investigation of host-to-activator energy transfer and surface losses in SrY2O4:Eu under VUV excitation

We have completed a study of the optical properties of SrY₂O₄:Eu³⁺ under vacuum ultraviolet (VUV) excitation. Reflectance measurements on the undoped material yield a calculated band gap of about 6.1 eV. Studies on the doped material indicate that Eu³⁺ occupies the Y(1) and Y(2) sites in this host. Host-to-activator energy transfer calculations indicate a preference for transfer to Eu³⁺ at the Y(2) site. Modeling of the transfer efficiency data leads us to estimate that about 35% of absorbed radiation is lost to the surface under excitation near the band edge.     

Synthesis and characterization of Ca2Sn1-xCexO4 with blue luminescence originating from Ce^4＋ charge transfer transition

Ce^4＋-doped Ca2SnO4 with a one-dimensional structure, which emits bright blue light, is prepared by using a solid-state reaction method. The x-ray diffraction results show that the Ce^4＋ ions doped in Ca2SnO4 occupy the Sn^4＋ sites. The excitation and emission spectra of Ca2Sn1-xCexO4 appear to have broad bands with peaks at - 268nm and -442nm, respectively. A long excited-state lifetime （-83μs） for the emission from Ca2Sn1-xCexO4 suggests that the luminescence originates from a ligand-to-metal Ce^4＋ charge transfer （CT）. The luminescent properties of Ca2Snl_xCexO4 have been compared with those of Sr2CeO4, which is the only material reported so far to show Ce^4＋ CT luminescence. More interestingly, it is observed that the emission intensity of Ca2Sn1-xCexO4 with a small doping concentration （x - 0.03） is comparable to that of Sr2CeO4 in which the concentration of active centre is 100%.