PL quantum yield

Core/shell-type nanoparticles ovm ated with higher band inorganic materials exhibit high PL quantum yield compared with uncoated dots d K to elimination of surface non-radiative recombination defects. Such core/shell structures as CdSe/CdS [6] and CdSe ZnS [7] have been prepared from organometaHic precursors. 

A modified SILAR system has been used to grow CdSe in CdS/CdSe core shell semiconductor nanocrystals.12 A cadmium precursor solution, with CdO dissolved with oleic acid in octadecane, was injected onto the substrate, and the Se solution (Se powder dissolved with tributylphosphine in octadecane) was similarly injected. The temperature of the reaction solution was 185 °C. A CdS outer layer in the CdS/CdSe/CdS colloidal quantum wells was deposited by alternating injections of cadmium and sulfur both in octadecane solutions at 230-240 °C. These structures showed high PL quantum yields (20-40%), relatively narrow emission bands, and tunable emission colors from about 520 to 650 nm depending on the number of CdSe monolayers. 

Many important photophysical properties, such as aggregation-induced emission (AIE),11,12 blue shift of PL emission in the crystal state relative to that of amorphous solid,13 extremely high photoluminescence (PL) quantum yields... 

Highly efficient green photoluminescence has also been realized from SCPs. Copolymers 11 (Fig. 5) derived from 2,7-fluorene and 2,3,4,5-tetraphenylsilole show absolute PL quantum yields up to 84%.28 A well-defined alternating copolymer 12 with a repeating unit made up of ter-(2,7-fluorene) and 2,5-silole possesses an absolute PL quantum yield >80%.29 SCPs 13 with a main chain structure of 3,6-carbazole-2,7-fluorene-2,5-silole also show absolute PL quantum yields up to 86%.30 An energy transfer copolymer 14 of 2,7-dibenzosilole and... 

Copolymers 15 (Fig. 6) derived from 2,7-fluorene and 2,5-dithienylsilole show red fluorescence via an energy transfer process.31 The APl could be 591 nm for copolymers with higher contents of 2,5-dithienylsilole. The absolute PL quantum yields (<30%) of the copolymers are somewhat lower than the green fluorescent SCPs. A copolymer 16 derived from 2,7-dibenzosilole and 4,7-dithienyl-2,l,3-benzothiadiazole show a better red fluorescence.26 The APL of the copolymer is at 629 nm, with an absolute PL quantum yield of 53%. 

In this chapter, we describe the synthesis of a series of self-assembled metal coordination polymers that show various color emissions from the violet to red spectral region with high PL quantum yields and good OLED efficiencies. 

Spectroscopic data of la—li, monomers of la—li, and model compound 1 (zinc(II) fe(V-phenyl salicylaldiminato) are listed in Table 2. The absorption spectra of these zinc(II) terpyridine polymers are similar, with absorption maxima at 286—290 and 320—391 nm. PL of these polymers span violet, blue, green, and yellow color. The PL quantum yields ( I>PL) range from 25% for lb and le to 77% for If in DM Ac. The PL values of the polymer thin films were determined using integrating sphere,23 which were found to vary from 0.15 to 0.55 0.05 (Table 2). 

Quinine sulfate in 0.1 N sulfuric acid was used as reference for determination of PL quantum yields. Excitation wavelength was 330 nm. 

Haase and co-workers have extensively studied the synthesis of high-quantum-yield nanophosphors such as Eu-, Tb- or Er-doped lanthanide phosphates (Riwotzki et al., 2000, 2001 Lehmann et al., 2004 Kompe et al., 2003 Lehmann et al., 2003). For example, the photoluminescence (PL) quantum yield of the CePO Tb core nanocrystals (4-6 nm) diluted... 

The Sm + ion with 4f -orbital configuration has numerous energy levels, even covering the NIR spectral range (Figure 11.27), which may be the reason that the PL quantum yields of most Sm complexes are very low. 

In 2007, the new dysprosium complex Dy(PM)3(TP)2 [PM= l-phenyl-3-methyl-4-isobutyryl-5-pyrazolone and TP = triphenyl phosphine oxide] was reported. A series of devices with various structures were fabricated to investigate the EL performance of Dy(PM)3(TP)2. The best device with the structure ITO/CuPc (15 nm)/Dy complex (70 nm)/BCP (20 nm)/AlQ (30 nm)/LiF (1 nm)/Al (100 nm) exhibited maximum brightness 524 cd m , current efficiency 0.73cdA and power efficiency 0.161mW The low PL quantum yield (3.5%) of the complex caused poor EL performance [75]. 

The NC synthesis was performed using an approach of Ref. [12]. These synthetic conditions were found to be optimal for preparation of CdTe NCs with a photoluminescence (PL) quantum yield of 40-60%. A Critical point drier (Spi Supplies) was used for the fabrication of aerogels. 

As mentioned above, rubrene is a prominent red-emitting molecule, as its PL quantum yield is 100% in dilute solution, but that emission is strongly suppressed in the solid state due to fission of the l1 to two triplets. Hence, it yields bright red OLEDs when incorporated as a guest in hosts such as TPD.69... 

The PL quantum yield r)pl. While r]pl of many dyes is close to 100% in solution, in almost all cases that yields drops precipitously as the concentration of the dye increases. This well-known concentration quenching effect is due to the creation of nonradiative decay paths in concentrated solutions and in solid-state. These include nonradiative torsional quenching of the SE,148 fission of SEs to TEs in the case of rubrene (see Sec. 1.2 above), or dissociation of SEs to charge transfer excitons (CTEs), i.e., intermolecular polaron pairs, in most of the luminescent polymers and many small molecular films,20 24 29 32 or other nonradiative quenching of SEs by polarons or trapped charges.25,29 31 32 In view of these numerous nonradiative decay paths, the synthesis of films in which r]PL exceeds 20%, such as in some PPVs,149 exceeds 30%, as in some films of m-LPPP,85 and may be as high as 60%, as in diphenyl substituted polyacetylenes,95 96 is impressive. 

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