Fluorescent doping

Another important early advance made by Tang et al. [7] is the use of fluorescent doping, i.e., the addition of a small percentage of an emissive fluorescent material into a host matrix. This can be used to alter the color of emission, in addition to improving the efficiency and the lifetime of devices. The technique of simultaneously vapor depositing the host and the fluorescent dopant material is now widely used in the field of OLEDs. 

Tanaka, A., Sawada, H., Takoshima, T., and Wakatsuki, N., New plastic optical fiber with polycarbonate core and fluorescence-doped fiber for high temperature, Proc. SPIE, 840, 19, 1987. 

Single molecules also have promise as probes for local stmcture when doped into materials tliat are tliemselves nonfluorescent. Rlrodamine dyes in botli silicate and polymer tliin films exliibit a distribution of fluorescence maxima indicative of considerable heterogeneity in local environments, particularly for the silicate material [159]. A bimodal distribution of fluorescence intensities observed for single molecules of crystal violet in a PMMA film has been suggested to result from high and low viscosity local sites witliin tire polymer tliat give rise to slow and fast internal conversion, respectively [160]. 

Fiq. 20a. The pulsed Raman spectrum of Mn-doped ZnSe single crystal using a detection interval of 200 nsec. Broad band fluorescence superimposed on a large instrumental scattered light component was observed. Recordings taken with ratemeter time constants (TC) of 1 sec and 10 sec are shown (37). 

Fiq. 20b. The pulsed Raman spectrum of Mn-doped ZnSe with a 1 /xsec detection interval. The fluorescent background was significantly reduced from that observed with a 200 nsec detection interval in Fig. 20a (37). 

Velapoldl et al. (64) used a similar approach but prepared fibers of uniform diameter (5-45 pm) from Inorganic Ion-doped glasses. The fluorescence parameters of these materials can be changed by substituting various Ions, such as Tb , Sm , Eu , Mn, UOj, Cu, and Sn. They show excellent stability under Irradiation using Incident excitation (measurement Imprecision of 1% under continuous Irradiation In the microscope for 24 h) and have a fluorescence flux density proportional to the fiber length. 

To enhance the formation of Ti species by reduction and nitration together, treatment with H2+N2 plasma and H2+Ar/N2+Ar (H2+Ar treatment followed by N2+Ar) were tried. However, there was no further improvement. H2+Ar/N2+Ar plasma treatment reduced the optimum treatment time to 20 minutes but improvement of photocatalytic activity imder fluorescent light was just 2.0 times. H2+Ar pretreatment seems to make substitutional doping of N easier through reduction reaction. 

Nanoparticles of Mn and Pr-doped ZnS and CdS-ZnS were synthesized by wrt chemical method and inverse micelle method. Physical and fluorescent properties wra cbaractmzed by X-ray diffraction (XRD) and photoluminescence (PL). ZnS nanopatlicles aniKaled optically in air shows higher PL intensity than in vacuum. PL intensity of Mn and Pr-doped ZnS nanoparticles was enhanced by the photo-oxidation and the diffusion of luminescent ion. The prepared CdS nanoparticles show cubic or hexagonal phase, depending on synthesis conditions. Core-shell nanoparticles rahanced PL intensity by passivation. The interfacial state between CdS core and shell material was unchan d by different surface treatment. 

Figure 13.2 Fluorescence micrographs of DOPC multi-layer patterns fabricated by dip-pen nanolithography, (a) An array of 25 contiguous line features. Red color is from doped rhodamine-labeled lipid, (b) A higher magnification of the region highlighted by the white square in (a), (c) Two-component patterns containing two different dyes. Green color is from doped NBD-labeled lipid.

Figure 13.5 (a) Fluorescence micrograph of the self-spreading lipid bilayer doped with a dye molecule. The lipid bilayer spread on an oxidized silicon wafer from a deposited lipid aggregate illustrated on the left, (b) A schematic drawing of the selfspreading lipid bilayer from the lipid aggregate. Adapted from Ref [48] with permission. 

Figure 11 Order parameter (P2) as measured by fluorescence emission (filled circles) and absorption dichroism (open squares) and order parameter

Many of the linear conjugated tricyclic systems have interesting fluorescence or other electrophysical properties. Bis-pyrazolepyridines such as compound 30 have been incorporated into polymers as fluorescent chromophores <1999JMC339>, and used in doped polymer matrices <1997JMC2323>. They are electroluminescent at 425 nm and photoluminescent at 427 and 430 nm in a poly(vinylcarbazole) matrix with a quantum efficiency of 0.8. 

A typical multilayer thin film OLED is made up of several active layers sandwiched between a cathode (often Mg/Ag) and an indium-doped tin oxide (ITO) glass anode. The cathode is covered by the electron transport layer which may be A1Q3. An emitting layer, doped with a fluorescent dye (which can be A1Q3 itself or some other coordination compound), is added, followed by the hole transport layer which is typically a-napthylphenylbiphenyl amine. An additional layer, copper phthalocyanine is often inserted between the hole transport layer and the ITO electrode to facilitate hole injection. 

The use of doped and undoped silica aerogels as multifunctional host materials for fluorescent dyes and other luminescent materials for display and imaging applications has been reported.278 Results have been presented on the PL spectra of undoped silica aerogels and aerogels doped with Er3+, rhodamine, and fluorescein.278... 

Huber Ch., Werner T., Krause Ch., Wolfbeis O.S., Novel Chloride-Selective Optode Based on Polymer-Stabilized Emulsions Doped with a Lipophilic Fluorescent Polarity-Sensitive Dye. Analyst 1999 124 1617. 

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