OPTICAL-PROPERTIES OF ERBIUM-DOPED ORGANIC POLYDENTATE CAGE COMPLEXES

The optical properties of different erbium (Er)-doped polydentate hemi spherand organic cage complexes are studied, for use in polymer-based planar optical amplifiers. Room temperature photoluminescence at 1.54 mu m is observed, due to an intra-4f transition in Er3+. The Er is dir ectly excited into one of the 4f manifolds (at 488 nm), or indirectly (at 287 nm) via the aromatic part of the cage. The luminescence spectr um is 70 nm wide (full width at half maximum), the highest known for a ny Er-doped material, enabling high gain bandwidth for optical amplifi cation. The absorption cross section at 1.54 mu m is 1.1x10(-20) cm(2) , higher than in most other Er-doped materials, which allows the attai nment of high gain. Measurements were performed on complexes in KBr ta blets, in which the complex is present in the form of small crystallit es, or dissolved in the organic solvents dimethylformamide and butanol -OD. In KBr the luminescence lifetime at 1.54 mu m is <0.5 mu s, possi bly due to concentration quenching effects. In butanol-OD solution, th e lifetime is 0.8 mu s, still well below the radiative lifetime of 4 m s estimated from the measured absorption cross sections. Experiments o n the selective deuteration of the near-neighbor C-H bonds around the Er3+-ion indicate that these are not the major quenching sites of the Er3+ luminescence. Temperature dependent luminescence measurements ind icate that temperature quenching is very small. It is therefore conclu ded that an alternative luminescence quenching mechanism takes place, presumably due to the presence of O-H groups on the Er-doped complex ( originating either from the synthesis or from the solution). Finally a calculation is made of the gain performance of a planar polymer waveg uide amplifier based on these Er complexes, resulting in a threshold p ump power of 1.4 mW and a typical gain of 1.7 dB/cm, (C) 1998 American Institute of Physics.