Transition-metal ions, infrared emission

Infrared diode laser spectroscopy, 46 119, 148 Infrared emission, transition,-metal ions, 35 334-335... 

Gudel and coworkers have reported during recent years many cases of (near) infrared emission from several transition-metal ions. This was only possible by the use of suitable detectors of radiation (e.g. a cooled germanium photo-detector) and careful crystal synthesis. Here we mention some examples. 

A. Infrared Emission from Transition-Metal Ions... 

Giidel and coworkers, in recent years, have reported many near infrared emissions from transition metal ions with "unusual valencies (V +(3d ), V (3d ), Ti (3d ), Mn5+(3d2) fl51). 

In this part, single activator-doped systems with multicolor emission are briefly introduced. The luminescent properties of a phosphor are basically determined by the host stmcture and the characteristics of the activator. Rare-earth ions and some transitional-metal ions are usually used as activators of phosphor. The energy-level spectra of some rare-earth ions, such as Eu ", Pr , Tb ", and Dy " contain several metastable multiplets that can offer the possibility of simultaneous emission in the blue, green, orange, red, and infrared wavelengths in different crystalline hosts. In turn, these are strongly affected by the host lattice (phonon frequency as well as the crystal stmcture), and the concentration of the activators decide the different color-emission intensities from 4 -4C transitions. The emissions of other rare-earth ions with —> / transition (Eu ", Ce " ), including transitional metal ions with... 

The term upconversion describes an effect [1] related to the emission of anti-Stokes fluorescence in the visible spectral range following excitation of certain (doped) luminophores in the near infrared (NIR). It mainly occurs with rare-earth doped solids, but also with doped transition-metal systems and combinations of both [2, 3], and relies on the sequential absorption of two or more NIR photons by the dopants. Following its discovery [1] it has been extensively studied for bulk materials both theoretically and in context with uses in solid-state lasers, infrared quantum counters, lighting or displays, and physical sensors, for example [4, 5]. Substantial efforts also have been made to prepare nanoscale materials that show more efficient upconversion emission. Meanwhile, numerous protocols are available for making nanoparticles, nanorods, nanoplates, and nanotubes. These include thermal decomposition, co-precipitation, solvothermal synthesis, combustion, and sol-gel processes [6], synthesis in liquid-solid-solutions [7, 8], and ionothermal synthesis [9]. Nanocrystal materials include oxides of zirconium and titanium, the fluorides, oxides, phosphates, oxysulfates, and oxyfluoiides of the trivalent lanthanides (Ln ), and similar compounds that may additionally contain alkaline earth ions. Wang and Liu [6] have recently reviewed the theory of upconversion and the common materials and methods used. 

Lanthanide p-diketonates are amongst the best smdied rare-earth luminescent complexes [58]. They are brightly luminescent and volatile so that incorporation into various electroluminescent materials is simple. Moreover their photophysical properties are easily tuned by a judicious choice of ancillary ligands. Indeed, conventional synthesis usually yields bis(hydrated) lanthanide tris(P-diketonates), but the two solvent molecules can be substituted by either a fourth diketonate anion or a donor ligand with adequate functionalisation as to provide convenient light harvesting and subsequent energy transfer onto the metal ion. It is noteworthy that not only visible but also near-infrared luminescence [59,60] is efficiently sensitised in lanthanide p-diketonates. In the case of Eu , some ternary complexes have quantum yields up to 85% [8] and the main asset of their luminescent properties is an emission essentially concentrated in the hypersensitive Dq transition... 

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