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Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1 were isolated from the rhizosphere soil of the selenium-hyperaccumulator legume Astragalus bisulcatus and waste material from a dumping site for roasted pyrites, respectively. Here, these bacterial strains were studied as cell factories to generate selenium-nanostructures (SeNS) under metabolically controlled growth conditions. Thus, a defined medium (DM) containing either glucose or pyruvate as carbon and energy source along with selenite () was tested to evaluate bacterial growth, oxyanion bioconversion and changes occurring in SeNS features with respect to those generated by these strains grown on rich media. Transmission electron microscopy (TEM) images show extra- or intra-cellular emergence of SeNS in SeITE02 or MPV1 respectively, revealing the presence of two distinct biological routes of SeNS biogenesis. Indeed, the stress exerted by upon SeITE02 cells triggered the production of membrane vesicles (MVs), which surrounded Se-nanoparticles (SeNPsSeITE02-G_e and SeNPsSeITE02-P_e with average diameter of 179 ± 56 and 208 ± 60 nm, respectively), as highlighted by TEM and scanning electron microscopy (SEM), strongly suggesting that MVs might play a crucial role in the excreting mechanism of the SeNPs in the extracellular environment. On the other hand, MPV1 strain biosynthesized intracellular inclusions likely containing hydrophobic storage compounds and SeNPs (123 ± 32 nm) under pyruvate conditioning, while the growth on glucose as the only source of carbon and energy led to the production of a mixed population of intracellular SeNPs (118 ± 36 nm) and nanorods (SeNRs; average length of 324 ± 89). SEM, fluorescence spectroscopy, and confocal laser scanning microscopy (CLSM) revealed that the biogenic SeNS were enclosed in an organic material containing proteins and amphiphilic molecules, possibly responsible for the high thermodynamic stability of these nanomaterials. Finally, the biogenic SeNS extracts were photoluminescent upon excitation ranging from 380 to 530 nm, whose degree of fluorescence emission (λem = 416–640 nm) was comparable to that from chemically synthesized SeNPs with L-cysteine (L-cys SeNPs). This study offers novel insights into the formation, localization, and release of biogenic SeNS generated by two different Gram-negative bacterial strains under aerobic and metabolically controlled growth conditions. The work strengthens the possibility of using these bacterial isolates as eco-friendly biocatalysts to produce high quality SeNS targeted to possible biomedical applications and other biotechnological purposes.

The near-infrared to visible upconversion properties of nanocrystalline Gd3Ga5O12:Er3+ (1 and 5%) were studied following excitation of the 4I9/2 exited state with 800 nm radiation. Intense green and red emissions were observed from the (2H11/2, 4S3/2) → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. The upconverted decay times in the 1% sample were identical compared to those obtained with 488 nm excitation, indicating that ESA was responsible for populating the upper emitting states. However, as the Er3+ concentration was increased to 5%, the upconverted decay times were lengthened and deviated from exponentiality, indicating the presence of energy transfer upconversion. In addition, an enhancement of the red (4F9/2 → 4I15/2) upconversion emission was observed in the 5% sample and occurred via an energy transfer process of the type (4I9/2, 4I11/2) → (4I13/2, 4F9/2).

Glasses of composition (x − 1)PbOؒ(100 − x)GeO 2 ؒ1Ln 2 O 3 , with x = 30 mol% (Ln = Nd, Eu, Er), 40 mol% (Ln = Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm), and 50 mol% (Ln = Eu, Er), have been prepared by quenching the oxidic melts. From the optical absorption and emission spectra in the ultravioletvisible-near-infrared (UV-VIS-NIR) region, the intensity parameters, spontaneous emission probabilities, branching ratios, radiative lifetimes, and, for selected NIR transitions, peak stimulated emission cross sections have been obtained. The trends observed in the intensity parameters have been discussed, as a function of the number of f electrons as well as a function of the lead content. As the amount of lead increases, the covalency of the Ln−O bond increases, the symmetry of the rare-earth site increases, and the dopant site distribution narrows. The peak stimulated emission cross sections rank among the highest found for oxide glasses.

Zinc tellurite glasses of compositions 19ZnO-80TeO 2 -1Ln 2 O 3 with Ln= Eu, Er, Nd and Tm were prepared by melt quenching. The absorption spectra were measured and from the experimental oscillator strengths of the f f transitions the Judd-Ofelt parameters V u were obtained. The values of the V u parameters are in the range usually observed for oxide glasses. For Nd 3 + and Er 3 + , luminescence spectra in the near infrared were measured and the stimulated emission cross sections | p were evaluated for some laser transitions. The high values of | p , especially for Nd 3 + , make them possible candidates for optical applications. Fluorescence line narrowing (FLN) spectra of the Eu 3 + doped glass were measured at 20 K, and the energies of the Stark components of the 7 F 1 and 7 F 2 states were obtained. A crystal field analysis was carried out assuming a C 26 site symmetry. The behaviour of the crystal field ratios B 22 /B 20 and B 44 /B 40 agrees reasonably well with the values calculated using the geometric model proposed by Brecher and Riseberg. The crystal field strength at the Eu 3 + sites appears to be very low compared to other oxide glasses.