Quantum laser dyes

D. Moses, High quantum efficiency luminescence from a conducting polymer in solution a novel polymer laser dye. Appl. Phys. Leu. 1992, 60, 3215. 

Polymers with specific functionalities can be realized by incorporating various dopants, such as laser dyes, rare earth ions, quantum dots, and functional chromophores into the host polymer. Chromophores are molecules or chemical groups as part of a larger molecule, and they have characteristic absorption bands in the... 

The most important xanthenes are the imino derivatives known as rhodamines, exemplified by rhodamine B (Cl Basic Violet 10) (3.23a), A. 543 nm and 552 nm and rhodamine 6G (Cl Basic Red 1) (3.23b), /L 530 and X 557 nm (Figure 3.11). These are intensively fluorescent dyes with quantum yields close to unity. Rhodamine 6G especially has found wide apphcation in dayhght fluorescent pigments (see section 3.5.2) and this ring structure has been much modified for use in many other outlets, especially as laser dyes (see section 3.5.3) and in biomedical applications (see section 3.5.6). 

Laser dye/Si02 gel CT AB/decanol/decane/ formamide (nonaqueous xE) TE0S/H20 (pH 1, HNO 3 10-2 M laser dye) Silica gels doped with laser dyes (rhodamine B, rhodamine 6G) gave fluorescence quantum yields indicating promise as candidate solid-state laser dye materials (49)... 

Several more recently studied CPs are, on the other hand, much more luminescent. For instance, the luminescence quantum yield of MEH-PPV in solution is 35%, and laser emission at 600 nm from a solution pumped at 530 nm by frequency-doubled Nd pulses has been reported, with outputs comparable to those of typical laser dyes [152]. 

We have indicated how a modest (1.3) enhancement in angular intensity can be obtained in cavity devices with Alq emissive layers. Further enhancements in angular intensity are possible by choosing emissive layers with narrower free-space emission spectra than Alq. Alq doped with small quantities of the laser dye pyrromethene 580 (PM) results in the emission spectrum of the system becoming narrower than that of Alq. This is result of resonance energy transfer33 from the excited states of Alq to the excited states of PM580. The full width at half-maximum of the luminescence drops from 100 nm to 45 nm. The spectra are shown in Fig. 4.12. The external quantum efficiency of noncavity devices is enhanced in comparison with devices with an undoped Alq emissive layer. For a device with a ITO/TAD/Alq+0.5%PM (20 nm)/Alq/Li (1 nm)/Al(200 m) structure, an external quantum efficiency of 1.8-2% photons/electron was measured. For comparison, equivalent LEDs without the pyromethene dye had an external quantum efficiency (with Li/Al cathodes) of 0.8%. 

Ormosils can possess excellent transparency when processing conditions are optimized. Moreover, they are typically nonporous. Their properties, as well as their low-temperature processing, make them ideal candidates as optical host media for a wide range of optically active species. These include laser dyes [51,53,55], photochromic molecules [52], second-harmonic-generating dielectric oxides [54], semiconductor quantum dots [53], and metallic quantum dots... 

Laser dyes are assumed to be relatively photostable. However, as Fig. 4.28 shows, the spectra change within a few seccmds. Under these conditions 7,7 -diethylamino-4-methylcoumarine (DEMQ undergoes jJiotodegrada-tion. The different photodegradation products demonstrate a change in absorption and fluorescence maxima. In addition, their fluorescence quantum yields differ. 

Neglecting the photo-degradation processes in laser dyes the partial photochemical quantum yields of stilbene-1 derivatives have been determined by evaluation procedures as given above [93]. In Section 4.3.2 a microprocessor controlled device is described [176], which allows convenient measurement of the data. Even an optical multi-channel analyser can be used [175]. 

In the case of the photoreactions of anthrone and anthraquinone only the intensity diagrams were used to support mechanistic considerations obtained by formal kinetic examinations using absorbance. However, in the process of the examination of the photostability of laser dyes, quantum yields have been determined applying the equations given in Sections 5.5.1 and 5,5.1.1. 

By this means quantum yields can be determined not only for these two dyes but for a large variety of laser dyes which have been presented in the literature [93]. The quantum yields depend on the amount of oxygen in solution and the wavelength of irradiation. 

In Section 5.5.3, a more sophisticated method has been given to correct measured fluorescence intensities influenced by the change in the photokinetic factor during the photoreaction. By these means the photochemical quantum yields of a large variety of laser dyes can be determined using the corrections according to eq. (5.157). Some structures of dyes used are... 

In Section 5.6.1.1 quantitative results for the partial photochemical quantum yields of the photoreaction of stilbene-1 were given. A photoisomerisation was assumed to be the mechanism as a first step. This proposal is supported by a reaction chromatogram of the photodegradation reaction of this laser dye. The two parts of the diagram (see Fig. 5.58) prove a photo-reversible isomerisation as a first step [190]. This information was used for the evaluation mentioned. 

G. Gauglitz, Determination of photochemical quantum yields using fluorescence data, demonstrated by laser dyes. Z. Phys. Chem. (Wiesbaden) N. F. 113 (1978) 217. 

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