Lanthanide ions upconversion

Following the introduction to size-dependent nanophenomena presented in the previous sections, we now focus our attention on the luminescence properties of lanthanide ions at additional sites or distorted structure existing in nanophases. Phenomena of prolonged luminescence lifetime, anomalous thermalization, upconversion luminescence, dynamics of long-range interaction with two-level-systems (TLS), and quantum efficiency are to be discussed. 

Table 2. Transition metal ions in doped halide lattices for which upconversion luminescence has been demonstrated, including relevant mechanistic and electronic-structural information. The lightest and heaviest lanthanides showing single-ion upconversion are also listed. Adapted from [17] ...

Here, we will give an overview on the work on NIR labels and probes based on lanthanide ions. The emphasis will be on the NIR luminescent ions (Yb , Nd ", Er ", Pr ", Ho ", Tm " ), which may be incorporated in complexes that can be excited by ultraviolet, visible or possibly NIR light. Alternatively, multiphoton excitation and lanthanide-based upconversion make possible the use of NIR... 

The other upconversion pathways are foremost relevant in doped inorganic materials. Multiionic mechanisms can be developed based on those fimdamental principles. The most frequent lanthanide ions for upconversion in inorganic materials are Pr +, Er +, and Tm +. Most of those inorganic materials use f- f transitions to achieve excited state absorptions. Lanthanide ions having both NIR and visible emission are thus needed. This limitation does not occur for two-photon absorption, which may use any lanthanide ion. For more details, the reader can refer to specific reviews. ... 

Solid-state lanthanide luminescent materials have the combined advantages of typical lanthanide luminescence and photophysical stability. In these materials, lanthanide ions are trapped into the rigid crystal host lattice, avoiding adverse quenching by environmental oscillators. Two types of luminescence modes, downconversion and upconversion, are known for lanthanide luminescence. Upconversion relates to a nonlinear optical process where two or more near-infrared (NIR) photons are absorbed sequentially to several real intermediate energy states and luminescence is emitted with a... 

A typical upconversion material is composed of two components, an inorganic host matrix and doping lanthanide ions (Figure 3). For achieving efficient ETU, effective energy transfer between the host matrix-embedded ions is essentially required, so the doped ions can also be divided into two types, activator (emitter) and sensitizer (absorber). 

Sensitizer In energy transfer upconversion (ETU) process, a sensitizer is generally a lanthanide ion (i.e., Yb +), which absorbs incident light strongly and transfers the absorbed energy to nearby emitter ions. A sensitizer serves as an energy reservoir for sensitizing activators. 

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