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[en] We have developed novel broad luminescent phosphors (La,Ce,Y)6Si4S17 including multiple substituted sites of Ce3+ . They have formed a triclinic structure (P − 1) with three kinds of coordination structures around Ce3+ ions. The broad photoluminescence (PL) spectra at the range from 430 nm to 700 nm were observed, and they can be respectively decomposed into three PL bands. Moreover, the correlation between the three PL bands and the three substitution sites for Ce3+ was confirmed through the PL spectra at 78 K and Van Uitert’s universal equation. (paper)
[en] An oxide grating fabricated with standard microlithographic processes and patterned with interference lithography was fabricated on a solid LuAG:Ce3+ phosphor chip about 0.2 mm thick. Integrating sphere emission measurement shows an increase of 8.1% in the emission band from 520 to 550 nm, with the majority of the increase coming at steeper emission angles. This process may be a practical way to increase solid state lighting efficiency. This technique was effective even though the phosphor was not optically flat.
[en] Photoluminescence of Ce3+- and Pr3+-activated Sr2GeO4 powders was measured between 17 and 600 K. For both ions strong 4fn−15dn→4fn (d-f) emission is observed at low temperatures, around 410 nm (Ce3+) and 280 nm (Pr3+). The Ce3+ d-f emission quenches starting at 150 K and disappearing completely just above room temperature. Pr3+ d-f luminescence shows an onset of quenching also around 150 K and disappears completely between 250 and 300 K. For Pr3+ quenching of the d-f emission was connected with an increasing intensity of the 3P0 luminescence at first and 1D2 emission at even higher temperatures. Both these 4fn→4fn emissions were observed up to 600 K. Based on the similar quenching temperatures, thermally stimulated photoionization of the 5d electrons from 5d level of Ce3+ or Pr3+ to the conduction band is proposed as the most probable mechanism for quenching of the d-f emissions.
[en] Mass-selected beams of atomic Ceq+ ions (q=2, 3, 4), of C82+ and of endohedral Ce-C82+ ions were employed to study photoionization of free and encaged cerium atoms. The Ce 4d inner-shell contributions to single and double ionization of the endohedral Ce-C82+ fullerene have been extracted from the data and compared with expectations based on theory and the experiments with atomic Ce ions. Dramatic reduction and redistribution of the ionization contributions to 4d photoabsorption is observed. More than half of the Ce 4d oscillator strength appears to be diverted to the additional decay channels opened by the fullerene cage surrounding the Ce atom
[en] Energy of 5d-levels of Ce3+ in numerous nitrides has become available due to the development of nitride phosphors recently. In this work, we have collected data on 5d-levels of Ce3+ and reconsidered the 5d centroid shift of Ce3+ in nitrides. The uniform standard, derived from the bond valence theory and the requirement for the high stability of the coordination polyhedron, has been proposed to determine the coordination number. The relationship between the 5d centroid shift of Ce3+, the polarizability of the anions and the electronegativity of the cations is revealed. The anion polarizability is linearly related to the inverse square of the average electronegativity of the cations; and the 5d centroid shift of Ce3+ can be well predicted by virtue of crystallographic data. This paper provides a feasibility to predict luminescence properties of Ce3+-doped nitrides.
[en] The nature of luminescence centers in CeO2 nanocrystals with varied oxygen stoichiometry has been investigated. It was shown that the luminescence of CeO2 is caused by the radiative relaxation in two different optical centers: the first one is Ce4+–O2− charge transfer state and the second one is Ce3+ ions. The ratio of Ce4+/Ce3+ centers depends on the amount of oxygen vacancies, therefore the variation of ceria stoichiometry allows changing the concentration of Ce4+–O2− and Ce3+ luminescence centers. Analysis of splitting of the excitation bands of Ce3+ luminescence has shown that oxygen vacancies in CeO2 nanocrystals are formed at the nearest-neighbor position to the cerium ion. -- Highlights: • The ceria CeO2 nanocrystals with varied oxygen stoichiometry were synthesized. • The luminescent properties were investigated under UV and VUV radiation. • The formation of two types of optical centers was shown. • Oxygen vacancies are formed at the nearest-neighbor position to Ce3+ ions
[en] In this article, five tetracyclines (TCs) showed ultrasensitive chemiluminescence (CL) based on the novel CL system of methoxylated Cypridina luciferin analogues (MCLA) and Ce(IV). It was found that the CL intensity of MCLA-Ce(IV) system was enhanced 30 times by adding 10 pmol chlortetracycline. Mechanisms of MCLA-Ce(IV)-TCs were investigated by CL spectra, radical scavengers and UV spectra. The results indicated that singlet oxygen, resulting from the reaction between Ce(IV) and TCs, was involved in the enhancement of CL phenomenon. This CL system coupling with flow injection analysis was developed for the determination of five common TCs. Linear ranged from 100 fmol to 20 pmol (r>0.999) with limit of detection of 20 to 50 fmol (S/N=3). The sensitivity of the present method is comparable to that of UPLC-MS/MS detection for TCs.
[en] The physical properties of the series CePd3Bex () have been studied. Introducing Be into CePd3 results in a drastic reduction of the Seebeck coefficient from 100 μV K−1 at 300 K to −2 μV K−1, respectively. Paramagnetism of Ce3+ free ions and metallic conduction dominate the physical properties. A structural transition at x = 0.25 is accompanied by a significant lowering of the Kondo temperature and leads to a successive suppression of the thermoelectric performance of CePd3Bex with increasing x. (paper)
[en] Highlights: • Pre- and post-oxidation Raman characterisation has been conducted on a variety of (U1-yCey)O2-x oxides. • The vacancies-related band increase and the small T2g band upshift undergone with Ce content reveal the presence of Ce3+. • A new Raman band found at ∼1070 cm−1 is proposed as the first overtone of the ∼535 cm−1 band associated with vacancies. • The protective effect of Ce on (U,Ce)O2 oxidation has been observed by the sole means of Raman spectroscopy.
[en] The influence of annealing in air at elevated temperatures on the absorption, luminescence and scintillation characteristics was studied for a set of Ce-doped aluminum garnet and perovskite single crystals. Positive effects consisting mainly in increase of light yield and decrease of afterglow were found to varying extent in all the materials. It is explained by the positive role of created stable Ce4+ center in scintillation mechanism and by decrease of deep trap concentration based on oxygen vacancies. - Highlights: • Effect of air annealing in Ce-doped aluminum garnets and perovskites studied. • Light yield increase in annealed samples is observed. • Effects of air annealing consist in Ce4+ creation and oxygen vacancy decrease.