Semiconductor nanoparticles luminescence emission

In a representative work, Chen and Rosenzweig34 were able to alter the selectivity of CdS nanoparticles to respond either to Zn2+ or Cu2+ simply by changing the capping layer. They showed that, while polyphosphate-capped CdS QDs responded to almost all mono- and divalent metal cations (thus showing no ion selectivity), luminescence emission from thioglycerol-capped CdS QDs was quenched only by Cu2+ and Fe3+, but was not affected by other ions at similar concentrations. On the other hand, the luminescence emission of L-cysteine-capped CdS quantum dots was enhanced in the presence of zinc ions, but was not affected by cations like Cu2+, Ca2+, and Mg2+. Using this set of QD probes, the authors described the selective detection of zinc and copper in physiological buffered samples, with detection limits of 0.8 pM and 0.1 p,M for Zn2+ and Cu2+, respectively. This was claimed to be the first use of semiconductor nanocrystals as ion probes in aqueous samples. 

Even larger probes of bent and kinked DNA are 40 A photoluminescent mineral colloidal particles of CdS [247-253]. These nanoparticles are approximately the size of proteins and can be made in a variety of sizes ( 20-100 A) and decorated with a variety of surface groups [267-279]. The emission spectrum of a nanoparticle solution depends on particle size and surface group synthetic procedures for CdS and other semiconductor nanoparticles have been developed so that the emission can be tuned throughout the visible spectrum and into the near infrared [267-279]. Moreover, the photoluminescence of CdS is sensitive to adsorbates [280-289], and thus these nanomaterials can function as luminescent chemical sensors. 

Absorption of and Emission fiom Nanoparticles, 541 What Is a Surface Plasmon 541 The Optical Extinction of Nanoparticles, 542 The Simple Drude Model Describes Metal Nanoparticles, 545 Semiconductor Nanoparticles (Quantum Dots), 549 Discrete Dipole Approximation (DDA), 550 Luminescence from Noble Metal Nanostructures, 550 Nonradiative Relaxation Dynamics of the Surface Plasmon Oscillation, 554 Nanoparticles Rule From Forster Energy Transfer to the Plasmon Ruler Equation, 558... 

The bead probes to be described in next two sections will require additional fluores-cence/luminescence emission detector(s). The number of these detectors depends on the number of different colors or wavelength regions of emission to be detected. A typical maximum that has currently been feasible with organic dye emitters has been about six. This may be augmented due to the observed narrow bandwidths (typically, 30-50 nm, and as low as 26 nm, reproducibly produced) of emission from semiconductor nanoparticles, which have been recently shown to allow 10 colors. ... 

Luminescence of Eu has not been detected in natural samples yet, but is well studied in artificially activated Zr02 (Gutzov et al. 1998 Gedanken et al. 2000 Reisfeld et al. 2000). The main emission occurs between the Dq level to the Fj multiplet with a decay time of approximately 0.5 ms (Eig. 5.13). The luminescence intensity is relatively weak, but may b e substantially increased by co-doping with nanoparticles of semiconductors, such as CdS. The origin of the... 

Gold nanoparticles are virtually not luminescent, but silver nanoparticles show plasmon emissions with reasonable quantum yields. Furthermore, the non-radiative decay, resulting in electron-hole pair generation, may be used for photosensitization of wide bandgap semiconductors (see Figure 7.5) [16,17]. Similar effects may also be observed as direct photoinduced electron transfer between metal surfaces and surface-bound molecules [18]. 

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