Luminescent upconversion/downconversion

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... 

Upconversion and Downconversion Dual-Mode Luminescence in One Nanoparticle... 

Table 1 The most important f-f transitions of NIR-luminescent lanthanides, and f-f transitions participating in upconversion (UC) and downconversion (DC) processes...

Scheme 9.6 State diagrams for the different chromophores present in [CrErCr(Ll)3](CF3S03)9 showing (a) the linear downconversion luminescence (excitation,/m// upward arrows, internal conversion, curled down arrows, energy transfer, dotted arrows emission,/u/l downward arrows) and (b) the nonlinear upconversion luminescence (excitation, full upward arrows internal conversion, curled down arrows ETU, dotted arrows emission, full downward arrows). Reprinted with permission from [28]...

Typically, the optimization of sunlight harvesting in PV devices by means of spectral managing coatings can be performed via three different luminescence processes upconversion (UC), downconversion (DC) (or quantum-cutting (QC)) and downshifting (DS) (see Figure 11.1). As a mle of thumb, UC layers are placed at the rear of the PV cell so as to collect transmitted photons, while DC and DS layers are placed on the front surface. 

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