A spectroscopic analysis of blue and ultraviolet upconverted emissions from Gd3Ga5O12:Tm3+, Yb3+ nanocrystals

The spectroscopic behavior of gadolinium gallium garnet (Gd3Ga5O12, GGG) nanocrystals codoped with 1% each of Tm3+ and Yb3+ prepared via a solution combustion synthesis procedure was investigated. Initial excitation of the codoped nanocrystals with 465.8 nm (into the 1G4 state) showed a dominant blue-green emission ascribed to the 1G4-3H6 transition as well as red and NIR emissions from the 1G4-3F4 and 1G4-3H5/3H4-3H6 transitions, respectively. Excitation at this wavelength (465.8 nm) showed the existence of a Tm3+ --> Yb3+ energy transfer process evidenced by the presence of the 2F5/2-2F7/2 Yb3+ emission in the NIR emission spectrum. The decay time constants proved that the transfer of energy occurred via the 3H4 state. Following excitation of the Yb3+ ion with 980 nm, intense upconverted emission was observed. Emissions in the UV (1D2-3H6), blue (1D2-3F4), blue-green (1G4-3H6), red (1G4-3F4), and NIR (1G4-3H5/3H4-3H6) were observed and were the direct result of subsequent transfers of energy from the Yb3+ ion to the Tm3+ ion. Power dependence studies showed a deviation from expected values for the number of photons involved in the upconversion thus indicating a saturation of the upconversion process. An energy transfer efficiency of 0.576 was determined experimentally.     

Monooxorhenium(V) complexes with the tridentate Schiff baseN-(2-hydroxyphenyl)salicylideneimine

Summary The reactions of the tridentate Schiff base ligandN-(2-hydroxyphenyl) salicylideneimine (HOPhsalH) with oxotetrachlororhenate (IV) have been investigated. The complexes (Bu₄N)[ReOCl₃(HOPhsal)], (Bu₄N)[ReOCl₂(OPhsal)],cis- [ReOCl(MeOH)(OPhsal)],trans-[ReOCl(MeOH)(OPhsal)] (1), trans-[ReOCl(OH₂)(OPhsal)] · Et₂O (2), trans-[ReOCl(OH₂)(OPhsal)] · Me₂CO,cis-[ReOCl(PPh₃)(OPhsal)],cis-[ReOCl(PMe₂Ph)(OPhsal)](3) have been synthesized and characterized. The crystal structures of(1), (2) and(3) have been solved from three-dimensional x-ray data by Patterson and Fourier methods and refined by least-squares methods to R 0.10 for(1), 0.042 for(2) and 0.059 for(3). In all the three complexes, the ligands surrounding the rhenium atom are at the apices of a distorted octahedron, with the equatorial ONO donor atoms of the tridentate Schiff base bent away from the O_oxo and toward the loosely bound MeOH in(1), H₂O in(2) and Cl in(t3). The fourth equatorial substituent is Cl (1 and2) and PMe₂Ph(3) and the rhenium atoms lie 0.30–0.37 Å above the best plane through the four equatorial atoms, in the direction of the O_oxo. All interatomic distances and angles are normal.