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Diffusion coefficients of fluorescent organic molecules in inert gases
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Image of FIG. 1.
FIG. 1.

Schematic of an OVPD reactor with a laser-induced fluorescence (LIF) capability to dynamically measure organic species concentration in the gas phase. Here, and are the mass flow rates of carrier gas injected in the source and the tube respectively, and are the source and tube temperatures, is the tube pressure, and PL is the photoluminescence.

Image of FIG. 2.
FIG. 2.

(a) Concentration of Alq as a function of time, , for a series of organic material pulses into the OVPD reactor and transported by Ar. The pulses are shown for several arrest times, . All pulses are generated with the following conditions: Source temperature  = 300 °C, source carrier gas mass flow rate  = 100 sccm, tube pressure  = 1.5 Torr, total carrier gas mass flow rate  = 200 sccm, and tube temperature  = 340 °C. All pulses are generated by a 3 s long injection from the organic material source. Following 6 s after injection, the travel of each pulse is arrested for a time, , by switching all carrier gas flow to the bypass line. The solid lines are fits by the EMG function with a fixed  = 4.6 s for all pulses. (b) Evolution of the pulse width, , with arrest time, , obtained from the EMG fits in (a). The solid line is a linear fit.

Image of FIG. 3.
FIG. 3.

Diffusion coefficients of Alq in N and Ar as functions of (a) tube temperature, , with a tube pressure of  = 1.5 Torr and (b) as a function of the inverse of with a  = 340 °C. The lines are theoretical diffusivities, calculated using the Chapman-Enskog theory.


Generic image for table
Table I.

Diffusion coefficients of Alq, ADN, SubPc, and rubrene in N and Ar measured experimentally and calculated using the Chapman-Enskog theory. and are the tube temperature and pressure, respectively.

Generic image for table
Table II.

Molecular properties used to parameterize the Chapman-Enskog theory. is the molecular mass, is the melting point, and are the maximum intermolecular attractive energy and the molecular diameter of species α, is the fractional anisotropy of the molecular shape, and is the magnitude of the molecular dipole.


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Scitation: Diffusion coefficients of fluorescent organic molecules in inert gases