Host Dependency of Boundary between Strong and Weak Crystal Field Strength of Cr3+ Luminescence.

Cr3+ doped near-infrared phosphors hold significant applications and generate considerable research interest. The critical parameter for assessing the strength of the crystal field for Cr3+ in the Tanabe-Sugano diagram is the boundary value of Dq/B, representing the ratio of crystal field splitting to the Racah parameter B. Nevertheless, there are conflicting values for this parameter, as reported in various studies, such as 2.1, 2.2, and 2.3 for C/B = 4.5-4.8. Moreover, some Cr3+ doped phosphors with wide-band emissions exhibit a Dq/B value that falls within the region of a contradictory strong field. In this study, we numerically determine the boundary value of Dq/B, which distinguishes between strong and weak fields. The results then demonstrate a dependence on the host material and are correlated with the values of Racah parameters B and C. This work resolves the inconsistency between the boundary values of Dq/B and the emission profile of Cr3+, providing researchers with a more profound comprehension of Cr3+ luminescence.

Trends in Atomic Parameters for Crystals and Free Ions across the Lanthanide Series: The Case of LaCl3:Ln(3+).

Analyses of the crystal field energy levels of the series LaCl3:Ln(3+) using a semiempirical Hamiltonian shows that only five ions (Pr, Nd, Pm, Dy, Ho) meet the criteria to avoid overfitting of the atomic part. A new parameter (SNES) has been introduced to represent the strength of the normalized electrostatic repulsion for these ions. This parameter varies linearly (R(2)adj = 0.9994, N = 5) with the reciprocal of the radius of the tripositive lanthanide ion, as expected from the form of repulsive Coulomb interaction. The Slater parameters from the crystal field analyses, F(k)(corr) (i.e., corrected for the effects of the two-particle component of the three-body operator associated with the T(2) parameter), exhibit an exponential variation with the number of electrons, n, in 4f(n). This is explained by reference to the radial part of a hydrogen-like wave function. The ratio of F(k)(corr) with the ab initio free ion Slater parameter F(k)(ab initio) varies linearly with n. Fitted parameters F(k)(corr: free ion) from the free ion data for Pr(3+) and Nd(3+) show that the corresponding ab initio values are between 14 and 27% too high. The spin-orbit coupling constant from crystal field analyses (ζ4f) exhibits a quartic variation with atomic number, and the ratio ζ4f/ζ4f(ab initio) follows an exponential growth model with n. The results serve to confirm the hypothesis that smooth trends can be observed across the Ln(3+) series for the fitted parameters despite the fact that the majority of experimental data is lacking.

Efficient doping and energy transfer from ZnO to Eu3+ ions in Eu(3+)-doped ZnO nanocrystals.

Successful doping of Eu3+ ions into ZnO nanocrystals has been realized by using a low temperature wet chemical doping technique. The substitution of Eu3+ for Zn2+ is shown to be dominant in the Eu-doped ZnO nanocrystals by analyzing the X-ray diffraction patterns, transmission electron microscopy images, Raman and selectively excited photoluminescence spectra. Measurement of the luminescence from the samples shows that the excited ZnO transfers the excited energy efficiently to the doped Eu3+ ions, giving rise to efficient emission at red spectral region. The red emission quantum yield is measured to be 31% at room temperature. The temperature dependence of photoluminescence and the photoluminescence excitation spectra have also been investigated, showing strong energy coupling between the ZnO host and Eu3+ ions through free and bound excitons. The result indicates that Eu3+ ion-doped ZnO nanocrystals are promising light-conversion materials and have potential application in highly distinguishable emissive flat panel display and LED backlights.

Speciated isotope dilution analysis of Cr(III) and Cr(VI) in water by ICP-DRC-MS.

An isotope dilution method has been developed for the speciation analysis of chromium in natural waters which accounts for species interconversions without the requirement of a separation instrument connected to the mass spectrometer. The method involves (i) in-situ spiking of the sample with isotopically enriched chromium species; (ii) separation of chromium species by precipitation with iron hydroxide; (iii) careful measurement of isotope ratios using an inductively coupled plasma mass spectrometer (ICP-MS) with a dynamic reaction cell (DRC) to remove isobaric polyatomic interferences. The method detection limits are 0.4 microg L(-1) for Cr(III) and 0.04 microg L(-1) for Cr(VI). The method is demonstrated for the speciation of Cr(III) and Cr(VI) in local nullah and synthetically spiked water samples. The percentage of conversion from Cr(III) to Cr(VI) increased from 5.9% to 9.3% with increase of the concentration of Cr(VI) and Cr(III) from 1 to 100 microg L(-1), while the reverse conversion from Cr(VI) to Cr(III) was observed within a range between 0.9% and 1.9%. The equilibrium constant for the conversion was found to be independent of the initial concentrations of Cr(III) and Cr(VI) and in the range of 1.0 (at pH 3) to 1.8 (at pH 10). The precision of the method is better than that of the DPC method for Cr(VI) analysis, with the added bonuses of freedom from interferences and simultaneous Cr(III) determination.

Synthesis and luminescence of nano-insulators doped with lanthanide ions.

This paper reviews the syntheses, particle-size measurements and various aspects of the optical spectra of lanthanide ion doped insulating nanomaterials, with the focus upon the sesquioxides, and it contrasts their behaviour with bulk materials.

2-year study of chemical composition of bulk deposition in a south China coastal city: comparison with east Asian cities.

Using the emission strengths of the precursor gases, the nature of soil in China, the ventilation power and half value rainout region length, the nss-SO42-, NO3-, Ca2+, and NH4+ concentrations, and pH of rainwater at Hong Kong and other cities of China and Japan are compared and rationalized. The chemical composition of Hong Kong bulk deposition from 1998 to 2000 is taken from our collection and analysis of 156 daily samples. The volume-weighted average (VWA) pH is 4.2 over the whole study period. Nonsea salt- (nss-) sulfate is the most abundant species in the samples, and the pH mostly depended upon the concentrations of the major species nss-SO42, NO3-, Ca2+, and NH4+. All species concentrations show higher levels in the cold season (especially NO3- and Ca2+), which indicates the dominant dilution effects in the warm season due to heavy rainfall and the influence of the continental outflow of pollutants during the cold season. For Hong Kong bulk deposition, the VWA pH is slightly lower in the cold season, and there is a slight decrease in VWA pH over the period from 1994 to 2000. The impact of acid rain in Hong Kong is briefly discussed.

Alterations in extracellular substances during the biofilm development of Pseudomonas aeruginosa on aluminum plates.

The chemical moieties during biofilm formation of Pseudomonas aeruginosa on aluminium plates were examined for a period of 17 days. The effect of fluid shearing upon biofilm formation has also been investigated. The Fourier transform infrared (FTIR) spectrum of the biofilm taken on the fifth day showed significant differences compared with the spectrum of the unattached bacterial cells, indicating that structural changes or modifications of the cell envelope had taken place during the development of the biofilm. Major changes were also observed in the spectrum during the subsequent development of the biofilm from day 5 to day 17. The increasing intensity of a band corresponding to the symmetric stretching mode of the carboxyl group indicated interactions between the carboxyl group and the aluminium surface. Increased bacterial colonization was also observed at the air-water interface of the aluminium plates when compared with the middle and the bottom parts. Changes in FTIR spectra of the biofilm at the bottom, at the middle, and at the air-water interface suggest that the mechanisms of bacterial attachment differed by a -COO(-) interaction at the air-water interface, and by both -COO(-) and NH3(+) groups beneath the water surface.