G. L. J. A. Rikken

Photo- and electroluminescence efficiency in poly(dialkoxy-p-phenylenevinylene)

Abstract This paper presents the dependence of luminescence efficiency on the degree of conjugation for a soluble poly(dialkoxy- p -phenylenevinylene), comparing the photoluminescence yields with the electroluminescence yields. Photoluminescence efficiency increases with the fraction of non-conjugated units for polymers both in the solid state and in solution. The highest external electroluminescence efficiency measured is 1.4% (photons/electron) for a polymer having approximately 10% non-conjugated units. Electroluminescence efficiency depends not only on the radiative recombination efficiency of the emitting material but also on carrier transport into and within the material.

Electroluminescence and photoluminescence efficiency of poly(p-phenylenevinylene) derivatives

Abstract Alkoxy, alkyl, and cyano derivatives of poly( p -phenylenevinylene) [PPV] are used as the emissive layers in light-emitting diodes [LEDs] to obtain luminescence from red to blue. We present the luminescence efficiency for these soluble PPV derivatives. comparing the photoluminescence [PL] yields with the electroluminescence [EL] yields. PL efficiency increases with the fraction of non-conjugated units. EL efficiency depends not only on the radiative recombination efficiency of the emitting material but also on carrier transport to and within the material. Efforts to improve the efficiency and long term stability of these polymer LEDs are challenged by efficient and balanced carrier injection.

Poled polymers for frequency doubling of diode lasers

We report on the design and characterization of methylmethacrylate copolymers with nonlinear optical 4‐alkoxy‐4’‐alkylsulfone stilbene sidechains, which are transparent down to 410 nm. A fairly stable, polar orientation has been obtained by means of electric field poling, resulting in a reasonably high nonlinearity (d33≤9 pm/V).

Schottky effect at a metal‐polymer interface

We report the observation of the Schottky effect at the interface between a metal and a semiconducting polymer by means of internal photoemission spectroscopy. The bias dependence of the barrier provides information on the electrical properties of the polymer.

Behavior of a rectifying junction at the interface between porous silicon and its substrate

The current injection into metal/porous Si/bulk Si diodes is investigated by transport and photoresponse measurements. Under low forward bias, the diode current is determined by the space charge region at the porous Si/bulk Si interface. The activation energy of the photovoltage shows that holes are injected into porous Si states which have little quantum confinement. This is discussed in terms of the confinement model for porous Si photoluminescence.

Efficient modal dispersion phase‐matched frequency doubling in poled polymer waveguides

We report the design, manufacture, and characterization of poled polymer multilayer waveguides for frequency doubling. Phase matching is obtained by using modal dispersion between the zeroth‐order fundamental lightwave and the first‐order second‐harmonic wave. By incorporating a very thin high refractive index satellite layer, the phase‐match condition can be fulfilled with concomitant large overlap between the two waves, resulting in efficient doubling.

Internal photoemission studies of metal/polymer interfaces

Abstract Internal photoemission is shown to be a valuable technique for studying electronic properties of buried metal/semiconducting polymer interfaces. The height of the observed barriers gives information on the nature of the interface, whereas the electric field dependence of the barrier height reflects important polymer properties. It is found that the barrier height is not determined by a simple electron affinity rule but by a high surface density of states.

Colourless nonlinear optical D-π-A polymers with sulphones as electron acceptors

Novel colourless side-chain methacrylate copolymers exhibiting relatively narrow charge-transfer bands at 335 nm and second-order optical nonlinearities up to d33= 4.3 pm V–1(at 1064 nm) have been synthesized and characterized.

Linear optical properties of frequency doubling polymers

Measurements of linear optical properties of methylmethacrylate copolymers with non-linear optical 4-alkoxy-4′-alkylsulfone stilbene side-chains are presented. From there two methods for phase matching are discussed; one aiming to equalize the refractive indices of the fundamental and the second harmnic wave, the other to suppress the destructive character of the interference. The matter of photo stability of frequency doubling polymers is also discussed.

Poled Polymer For Frequency Doubling Of Diode Lasers

Aligning polar molecules imbedded in a polymer matrix by means of a high electric field, as demonstrated by Havinga and van Pelt,’ can introduce a significant polar orientation. This makes these materials suitable for secondorder nonlinear optical (NLO) effects, like electro-optical modulation2’3 and second-harmonic generation (SHG) .3,4 Especially for this last purpose polymeric materials are very promising, as they can easily be applied in optical waveguide geometries, thereby transforming low powers like those emitted by diode lasers into high intensities and consequently giving high conversion efficiencies. However, up to now no poled polymer has been reported that can be used to double the frequency of the emission of the common AlGaAs-GaAs laser diodes (/2 820 nm) . In this letter we describe polymers that were specifically designed for this purpose and present the optical properties that affect their performance in this specific application. The major requirements for the NLO moiety are a high first-order hyperpolarizability /3( 2w;w,o) and complete transparency at both the fundamental and the second-harmonic wavelength. As a small separation between the charge transfer (CT) band and the second harmonic gives a large resonant enhancement to fi (Ref. 3) a narrow CT band is obviously advantageous. After having screened a large number of chromophores for their linear and nonlinear optical properties,5 we have selected some stilbene compounds containing an alkylsulfone group as electron acceptor and an alkoxy group as electron donor, as favorable candidates. Some relevant properties of these molecules are listed in Table I.