Luminescence upconversion

Shen, J. Zhu, Y. Chen., C. Yang, X. Li, C., Facile Preparation and Upconversion Luminescence of Graphene Quantum Dots. Chem. Common. 2011,47 2580-2582. 

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. 

Fig. 18. Upconversion luminescence from ZnS Eu3+ nanocrystals. The emission following excitation at 929 nm is significantly stronger than the emission following excitation only a few nanometers away. For comparison, a PL spectrum is shown as well (reprinted with permission from Chen et al. (2004a, 2004b, 2004c)).

Rare Earth Materials with Upconversion Luminescence for Bioimaging... 

Rare Earth Complexes with Upconversion Luminescence... 

Figure 13.36 Upconversion luminescence spectrum of the Y Er-Yb co-doped coordination polymer [(Y Er-Yb)(oba)(ox)o.5(H20)2]n [113]. (Reproduced from Inorganica Chimica Acta, 362, C. Y. Sun et al., Assembly and upconversion luminescence of lanthanide-organic frameworks with mixed acid hgands, 325-330, 2009, with permission from Elsevier.)...

Rare Earth Upconversion Luminescence Nanophosphors as Bioimaging Nanoprobes... 

Figure 13.43 In vivo upconversion luminescence imaging of subcutaneous HeLa tumor-bearing athymic nude mice (right hind leg) after intravenous injection of (A) UCNPS-NH2 or (B) UCNPs-FA. All images were acquired under the same instrumental conditions (power density approximately 120 mW cm on the surface of the mouse) [129]. (Reproduced from fiiomafen a/i, 30, L.Q. Xiong ef a/., Synthesis, characterization, and in vivo targeted imaging of amine-functionalized rare-earth up-converting nanophosphors, 5592-5600, 2009, with permission from Elsevier.)...

Weng, D.R, Zheng, X.J., Chen, X.B., etal. (2007) Synthesis, upconversion luminescence and magnetic properties of new lanthanide-organic frameworks with (4 )2(4, 6, 8 ) topology. European Journal of Inorganic... 

Wang, L.Y, Yan, R.X., Hao, Z.Y., etal. (2005) Fluorescence resonant energy transfer biosensor based on upconversion-luminescent nanoparticles. Angewandte Chemie International Edition, 44, 6054—6057. 

The minimum prerequisite for generation of upconversion luminescence by any material is the presence of at least two metastable excited states. In order for upconversion to be efficient, these states must have lifetimes sufficiently long for ions to participate in either luminescence or other photophysical processes with reasonably high probabilities, as opposed to relaxing through nonradiative multiphonon pathways. The observed decay of an excited state in the simplest case scenario, as probed for example by monitoring its luminescence intensity I, behaves as an exponential ... 

As shown in Figs. 3 and 4, this combination of excitation scans and time dependence measurements can be used to determine the mechanism responsible for upconversion luminescence in a simple three-level system. By extension, the same approach can be used in studies of more complicated upconversion systems constructed from the basic mechanistic building blocks of absorption and energy transfer. 

Thus, whereas GSA/ESA upconversion luminescence under low-power conditions shows the anticipated quadratic power dependence, that observed under high-power excitation conditions is expected to show only a linear dependence on pump power, exactly as in the GSA/ETU case (Eqs. 15 and 18). The intermediate-level population in a GSA/ESA system, however, remarkably becomes independent of changes in power at high powers when 2 = 2a (Eq. 21), in contrast with the high-power P behavior of the intermediate-level population in the GSA/ETU mechanism (Eq. 17). When ki = 25 GSA/ESA process the high... 

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