Butyl-PBD

Butyl-PBD [2-(4-t-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole] BBOT [2,5-bis(5-r-butylbenzoxazol- 354 367 382 ... 

The primary scintillator converts excitation energy into light. Two commonly used primary scintillators are PPO (2,5-diphenyl-oxazole) and butyl-PBD (2-(4 -tert-butyl-phenyl)-5-(4 -biphenyl)-l,3,4-oxadiazole). The pulse voltage produced by butyl-PBD is about 20% greater than that produced by PPO, but its usefulness is reduced because of its limited solubility. Suitable concentrations of PPO and butyl-PBD are about 5 g/1 and 7 g/1 respectively. With alkaline samples butyl-PBD produces a brownish colour in the scintillation cocktail. In highly quenched samples, a higher concentration may be required for optimum efficiency. 

A suitable mixture for toluene-soluble materials is toluene containing 5 g PPO/1 or 7 g butyl-PBD/1 0.1 g POPOP or dimethyl-POPOP/1. This mixture cannot be used for measuring the radioactivity in aqueous samples since water is immiscible with toluene. A further solvent (secondary solvent) miscible with both water and primary solvent must be added to this mixture to enable water to be incorporated. This amount of aqueous solution which can be incorporated in a particular mixture without phase separation depends on the identity of the secondary solvent, the relative proportions of primary and secondary solvents and the temperature. 

Other widely-used electron-transporting materials include 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-l,3,4-oxadiazole (butyl-PBD), which is essentially nonemis-sive and often introduced between the cathode and the emitting layer precisely for that reason, and 3-(4-Biphenylyl)-5-(4-tert-butylphenyl) l-phenyl-l,2,4-triazole (TAZ-1).6,74... 

A subsequent paper from two MIT groups [12] reported on a single-layer device where CdSe NCs were homogeneously distributed within a polymer layer (70-120 nm thick) of PVK as a hole-conducting component that additionally contained an oxadiazole derivative (butyl-PBD) as an electron-transporting molecular species. 

Following these recent successful developments, trilayer hybrid NC/polymer devices were reported, constituting a film of CdSe/ZnS NCs a few monolayers thick sandwiched between films of PVK (hole transporter) and butyl-PBD (electron transporter) [23]. All the layers were deposited by a spin-coating technique from dissimilar solvents (either organics or water). These devices showed 20 times the external quantum efficiency (0.2 %) and less than half the threshold voltage of a single-layer device based on the PVK/NC/PBD blend. These improvements upon going from a blend to a trilayer structure were attributed to more balanced carrier conduction to and enhanced recombination in the NC layer. 

Commercial solgel (emulsion) scintillators used were Aquasol II and Biofluor (New England Nuclear), Beckman GP (Beckman Instr.), and PCS (Amersham Corp.). Solvents used were p-xylene (ICN spectral grade) and toluene (Packard "Puresolv") and the scintillators were p-bis-Co-methylstyryl)-benzene (bis-MSB from Eastman Kodak) and 2-(4 -t-butylphenyl)-5-(4"-biphenylyl)-1,3,4-oxadiazole (butyl-PBD from ICN). The chelating agent was di-2-ethylhexyl phosphoric acid (HDEHP) obtained from K K Laboratories and used without further purification. Radionuclide solutions of known radioactivity concentration were supplied by other workers in the NBS Radioactivity Group (Mann, 1979). 

After Soluene 350 treatment, Permablend III (Packard Instrument Company Inc.) 5.1 g/ 1000 ml toluene was used as scintillation fluid. This fluid was also used in some of the in situ experiments. However, in this case butyl-PBD (Ciba-Geigy Inc.)... 

B. The slices were soaked in 3 ml ethylene glycol overnight with occasional stirring. To remove the ethylene glycol the slices were washed twice with 3 ml alcohol (99.5%) and then soaked overnight in 3 ml of this medium. The alcohol was then replaced by 3 ml toluene. About 3 hours later, when the slices were completely transparent, the toluene was exchanged for either (1) 5 ml butyl-PBD scintillation fluid, or (2) 5 ml Permablend III scintillation fluid. One hour later the radioactivity was analysed. 

D. The gel slices were treated according to B ( 1 or 2 ) or C ( 1 or 2 ). After the radioactive analysis the slices prepared according to B2 or C2 were treated overnight with 0.2 ml Soluene 350 and 0.05 ml bidistilled water. After addition of the original sampels of scintillation fluid the vials were treated as in A. (The Soluene 350 and the water can also be added to the Permablend III Scintillation fluid, but the subsequent swelling of the gel slices will then take much more time.) The Bl and Cl slices had to be rinsed twice in 3 ml toluene and soaked for at least 3 hours in this medium prior to Soluene 350 treatment. This was to ensure that only traces of butyl-PBD would remain. (Butyl-PBD reacts with Soluene 350 and produces... 

Butyl-PBD or BBOT may be substituted for PPO and DM-POPOP for Bis-MSB. The quantities used vary considerably and reference [73] should be consulted for further details. 

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