Photoluminescence quantum yield

The solution photoluminescence quantum yields of the copolymers are high (0.4-0.8) and indicate a great potential in light emission applications [60, 64-69],... 

Some of the derivatives 96 show high photoluminescence quantum yields of up to 73%, and can be applied as blue and green polymeric emitters in organic materials-based LEDs [122]. 

The choice of new complexes was guided by some simple considerations. The overall eel efficiency of any compound is the product of the photoluminescence quantum yield and the efficiency of excited state formation. This latter parameter is difficult to evaluate. It may be very small depending on many factors. An irreversible decomposition of the primary redox pair can compete with back electron transfer. This back electron transfer could favor the formation of ground state products even if excited state formation is energy sufficient (13,14,38,39). Taking into account these possibilities we selected complexes which show an intense photoluminescence (0 > 0.01) in order to increase the probability for detection of eel. In addition, the choice of suitable complexes was also based on the expectation that reduction and oxidation would occur in an appropriate potential range. 

Remarkably enough, 47 is a blue dye with a high photoluminescence quantum yield and, nevertheless, a high photochemical stability. Figure 7 shows the spectra of the different rylenetetracarboxdii-mide oligomers. 

Mattoussi H, Murata H, Merritt CD, Iizumi Y, Kido J, Kafafi ZH (1999) Photoluminescence quantum yield of pure and molecularly doped organic solid films. J Appl Phys 86 2642-2650... 

Similar results (a significant decrease of the photoluminescence quantum yields) were observed for thiophene-thiophene-S,S-dioxide copolymers containing 3,6-dimethoxyfluorene 560 (03MM8986) and carbazole 561 (02MM8413) (with 0F = 20-25% in solution). 

All the copolymers showed similar absorptions with Lmax at 470 nm, which was more intense for polymers with higher thiophene content. In contrast, their emission colors were progressively red shifted with increasing thiophene-based comonomer content. Copolymer 596a emitted bright red light (620 nm) with reasonably high photoluminescent quantum yields (34-69%). 

Figure 26. Experimental photoluminescence quantum yields for Mn2+ CdS nanocrystals, plotted versus Mn2+ concentration (a) for the long-lived yellow emission from Figure 25 (b) for the shortlived red emission from Figure 25. The solid lines represent the proportion of particles with (a) 1 and (b) 2-5 Mn2+ dopant ions, as described by Eqs. 1 and 2. [Adapted from (82).]...

The /3-diketonate [Nd(dbm)3bath] (see figs. 41 and 117) has a photoluminescence quantum efficiency of 0.33% in dmso-7r, solution at a 1 mM concentration. It has been introduced as the active 20-nm thick layer into an OLED having an ITO electrode with a sheet resistance of 40 il cm-2, TPD as hole transporting layer with a thickness of 40 nm, and bathocuproine (BCP) (40 nm) as the electron injection and transporting layer (see fig. 117). The electroluminescence spectrum is identical to the photoluminescence emission the luminescence intensity at 1.07 pm versus current density curve deviates from linearity from approximately 10 mA cm-2 on, due to triplet-triplet annihilation. Near-IR electroluminescent efficiency <2el has been determined by comparison with [Eu(dbm)3bath] for which the total photoluminescence quantum yield in dmso-tig at a concentration of 1 mM is Dpi, = 6% upon ligand excitation, while its external electroluminescence efficiency is 0.14% (3.2 cdm-2 at 1 mAcm-2) ... 

A single-layer OLED with [Er(acac)3phen] doped into a 80-nm thick film of PVK (see fig. 117) prepared by spin-coating and deposited on an ITO electrode, and with a 100-nm lithium-doped (0.1%) aluminum cathode has also been tested and shows an onset voltage of about 12 V for electroluminescence (Sun et al., 2000). [Er(dbm)3bath] has a photoluminescence quantum yield of 0.007% in dmso-7fl at 1 mM concentration the OLED based on this compound and similar to the one described above for Ndm has a NIR external electroluminescence efficiency of 1 x 10-6 (Kawamura et al., 2001). 

The oligomers 23 and 24a-c show enhanced solubility and increased glass transition temperatures when compared to their linear counterparts 25 and 26 (Scheme 3.10). No melting transition is observed for 23 whereas the linear molecule 25 (Scheme 3.10) melts at 254 °C. The electronic absorption spectra of the cruciforms 23 and 24a-c exhibit structureless, broad absorption peaks. Assuming a nonplanar ground state, the also featureless emission spectra indicate no significant increase of planarity upon photoexcitation. In addition, the cruciform molecules 23 and 24a-c show lower photoluminescence quantum yields (41-70%)... 

Spin-orbit coupling not only governs the amount and pattern of ZFS of the emitting triplet state, but it is also of dominant importance for the radiative emission decay rates and thus for the photoluminescence quantum yields. These properties are crucial for the suitability of triplet emitters in OLEDs. In conclusion, detailed spectroscopic studies of compounds triplet state properties in combination with... 

Eu(L )3(DDXPO) and Eu(L )3(DPEPO) were recently synthesized and structurally characterized (see Eigures 2.24 and 2.25), with the coordination polyhedra being a distorted square antiprism [34]. The former complex has a solid-state photoluminescence quantum yield of 48%, about two times higher than that of the latter (28%). 

A particularly interesting study that exemplifies the effect of nano-confinement is one where poly(phenylene vinylene) PPV, a luminescent polymer, was incorporated into the channels formed from these polymerized hexagonal phases [78]. These hexagonal PPV nanocomposites exhibited a significant enhancement in the photoluminescence quantum yields, from ca. 25 to 80%. The origin of this enhancement is ascribed to the prevention of the formation of poorly emissive inter-chain excitonic species as a result of the confinement of the PPV chains into well-defined and well-separated nanochannels. An important feature of these nanocomposites was that they could be readily processed into thin films and fibres and, more importantly, macroscopic alignment of the channels encapsulating the PPV chains led to polarized emission [79]. 

TABLE 8.1. Photoluminescence Quantum Yields of Selected Para-phenylene-Type Oligomer and Polymer Films and Solutions. 

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