Photoluminescence sample preparation

Photoluminescence spectroscopy is used to analyze the electronic properties of semiconducting CNTs [64]. The emission wavelength is particularly sensitive to the tube diameter [65] and chemical defects [66], However, a more dedicated sample preparation is required in order to eliminate van der Waals and charge transfer interactions between bundled CNTs. This can be done via ultrasonication or treatment of the bundles with surfactants that separate individual CNTs and suppress interactions between them [67]. 

Our investigation of sNPS showed that the samples prepared by the chemical etching method described above have consistent photoluminescence, conductivity and photoconductivity properties, which have remained unchanged over 5 years. sNPS structure was investigated by scanning electronic microscopy (Fig. 9.1). 

From photoinduced absorption, luminescence and electron spin resonance observations, the dominant photocarriers generated in the polymer were shown to be polarons and bipolarons [189-191]. It was found that the magnitude of photoinduced absorption is rather independent of the condition of sample preparation whereas the photoluminescence intensity is strongly influenced. The results suggest that the luminescent exciton does not play a primary role in the photogeneration of polaronic species. 

All pure solvents and substrates used for the sample preparation were characterized also by means of Raman and photoluminescence spectroscopy. 

Figure 4.11 Photoluminescence of quantum dots near Ag nanoprisms with a series of excitation wavelengths. (A) Schematic diagram of sample preparation Ag nanoprisms (NP) are attached to a 3-aminopropyItrimethoxysilane-treated glass coverslip and overcoated with a layer of quantum dot-doped PMMA (B) Darkfleld image showing locations of Ag nanoprism (C) scattering spectra of each of the labeled nanoprisms in (B). Correlated quantum dot photoluminescence images excited with (D) 410 nm, (E) 440 nm, (F) 470 nm, (G) 490 nm, (H) 570 nm, and (I) 590 nm light. Adapted from reference 43.

Chemiluminescence and photoluminescence are other forms of interference that can reduce the accuracy of LS techniques. Chemiluminescence describes the emission within the scintillation cocktail of photons that result from a chemical reaction common initiators are samples with an alkaline pFl or the presence of peroxides. Photoluminescence can occur when the scintillation cocktail is exposed to ultraviolet light. Some substances in the cocktail, notably the scintillator, are excited and then emit light when the species return to ground state. The effect of photoluminescence is reduced in LS systems by decay when the sample train is held in a dark environment for a few minutes prior to counting. On the other hand, chemiluminescence may have a slow decay rate that requires a change in sample preparation to eliminate the chemical that causes it. Some LS systems identify luminescence by pulse shape and indicate its relative extent. 

Figure 14.26. Photoluminescence of a polythiophene sample prepared from chemical oxidation of a silylated 4-thiophene, pTh-C4 (a) before, thermal annealing, (b) after thermal annealing, >1 = 5145 A.

Fig. 19 (a) Optical absorption and (b) photoluminescence spectra of CdSe and CdSe QDs capped with different concentration of cytosine. Sample A is as-prepared QDs and Samples B and C are capped QDs. (Adapted from [75])... 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

The adsorption of CO molecules is often used to probe surface Cu+ sites (107, 236). After evacuation of Cu(II)zeolite samples at 973 K, the EPR signal assigned to the copper(II) species become weak and can hardly be observed, indicating that the Cu " ions were reduced to Cu+ (see Section IV.D.2.a). With the Cu(l)zeolite catalysts prepared in this way, the photoluminescence was observed upon excitation at about 300 nm (Fig. 31). The... 

Fig. 55. Phololumiiiescence (a) and its excitation spectrum (b) of Cu(I)ZSM-5 aitalysl and the effect of CO addition on the photolumincscencc (1-4). Catalyst was prepared by evacuation of the original Cu(II)ZSM-5 sample (1.9 wt% as Cu metal) at 973 K. Addition of CO was carried out at 77 K. CO pressure (Pa) 1, 173 2, 306 3 and 3 (excitation spectrum of the photoluminescence spectrum 3), 372 4, 2660 [reproduced with permission from Yania-shita et al. (7iSd)].

In Figs 4a + 4b the relationship between efficient luminescence and localization of charge carriers is clearly demonstrated.The sample shows no luminescence but a strong microwave absorption signal due to the delocalized electrons, as prepared. After oxidation and treatment in forming gas (FG) there is eflBcient photoluminescence (PL) but the microwave absorption has vanished due to the localization of the electrons in states at the Si-Si02 interface (see Fig. 5). 

Fe-passivated porous silicon (PS) with non-degrading photoluminescence (PL) was prepared by treating P/P+-type, boron-doped single crystal (111) Si wafers at 140 °C in an aqueous solution with 40 wt% HF and 0.3 M Fe(N03)3 (volume ratio, 7/6) [8, 9j. As shown in Figure 7.2, for freshly prepared samples, the PL peak intensity is 2-2.5 times stronger than that of ordinary PS. Furthermore, unlike... 

One of the great issues in the field of silicon clusters is to understand their photoluminescence (PL) and finally to tune the PL emission by controlling the synthetic parameters. The last two chapters deal with this problem. In experiments described by F. Huisken et al. in Chapter 22, thin films of size-separated Si nanoparticles were produced by SiLL pyrolysis in a gas-flow reactor and molecular beam apparatus. The PL varies with the size of the crystalline core, in perfect agreement with the quantum confinement model. In order to observe an intense PL, the nanocrystals must be perfectly passivated. In experiments described by S. Veprek and D. Azinovic in Chapter 23, nanocrystalline silicon was prepared by CVD of SiH4 diluted by H2 and post-oxidized for surface passivation. The mechanism of the PL of such samples includes energy transfer to hole centers within the passivated surface. Impurities within the nanocrystalline material are often responsible for erroneous interpretation of PL phenomena. 

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