Stephan Haubold

Synthesis and surface modification of amino-stabilized CdSe, CdTe and InP nanocrystals

Abstract CdSe, CdTe and InP nanocrystals were prepared by an organometallic synthesis using mixtures of highly boiling primary amines and trioctylphosphine (TOP) as the coordinating solvent, and were characterized by powder XRD, SAXS, HRTEM, absorption and luminescence spectroscopy. The use of amines allowed us to obtain small crystalline nanoparticles for all materials investigated. In all cases, as-prepared colloids show rather narrow particle size distributions which can be further improved by standard size selective precipitation. Amino-capped II–VI nanocrystals show strong size-dependent band edge photoluminescence (PL). CdSe nanocrystals with the mean particle size in the range of 1.2–3.0 nm exhibit emission from blue to green with room temperature quantum yields of 15–20%. CdTe nanocrystals (2.5–5.0 nm size range) show a PL tunable from green to red with quantum yields up to 65% at room temperature. InP nanocrystals (1.5–4.0 nm size range) possess a weak emission (

Strongly Luminescent InP/ZnS Core–Shell Nanoparticles

The wide-bandgap semiconducting material, zinc sulfide, has been coated on indium phosphide nanoclusters to a 1-2-Å thickness. The resulting InP-ZnS core-shell particle (as shown in the TEM image; scale 1 cm=5 nm) exhibits bright luminescence at room temperature with quantum efficiencies as high as 23 %.

Cooperative effects in π-ligand bridged dinuclear complexes XXII. New dinuclear bis(cyclopentadienediyl)ketone complexes containing molybdenum, tungsten, cobalt and iron

Abstract Hydrolysis of the siloxyfulvene compounds {M}[η 5 -C 5 H 4 C(OTMS)(C 5 Me 4 )] ({M}=Mo(CO) 3 Me: 1a ; {M}=W(CO) 3 Me: 1b ) affords {M}[η 5 -C 5 H 4 C(O)(C 5 Me 4 H)] ({M}=Mo(CO) 3 Me: 3a ; {M}=W(CO) 3 Me: 3b ) which are suitable precursors for the synthesis of dinuclear complexes. The reactivity of the molybdenum and the tungsten compounds shows remarkable differences: heating of 3a with Co 2 (CO) 8 in the presence of 3,3-dimethylbut-1-ene reveals the heterodinuclear complex Me(CO) 3 Mo[(η 5 ( Mo )–C 5 H 4 )C(O)(η 5 ( Co )–C 5 Me 4 )]Co(CO) 2 ( 4a ) along with the homodinuclear complex (CO) 2 Co[(η 5 -C 5 H 4 )C(O)(η 5 -C 5 Me 4 )]Co(CO) 2 ( 5 ), the comparable reaction of 3b with Co 2 (CO) 8 results in the formation of the heterodinuclear complex Me(CO) 3 W[(η 5 ( W )–C 5 H 4 )C(O)(η 5 ( Co )–C 5 Me 4 )]Co(CO) 2 ( 4b ) only. The metal–metal bound complexes [(η 5 ( M )–C 5 H 4 )C(O)(η 5 ( M ′)–C 5 Me 4 )]MM′(CO) 6 ( M–M′ ) (M=W, M′=Mo: 8 ; M=M′=W: 9 ; M=M′=Mo: 10 ) are synthesized from the reaction of 3a or 3b with M′(CO) 3 (EtCN) 3 (M′=Mo, W). When Mo(CO) 6 is used in place of Mo(CO) 3 (EtCN) 3 10 can also be obtained in addition to [(η 5 -C 5 H 3 Me)C(O)(η 5 -C 5 Me 4 )]Mo 2 (CO) 6 ( Mo – Mo ) ( 12 ) as an unexpected by-product. In complex 12 the cyclopentadienyl ligand is regioselectively methylated in the vicinal position to the bridge-head atom. The synthesis of [(η 5 ( Mo )–C 5 H 4 )C(O)(η 5 ( Fe )–C 5 Me 4 )]MoFe(CO) 5 ( Mo–Fe ) ( 14 ) is achieved by reaction of 3a with Fe(CO) 3 (C 8 H 14 ). An X-ray diffraction study of the mononuclear siloxyfulvene Me(CO) 3 W[η 5 -C 5 H 4 C(OSiMe 2 t -Bu)(C 5 Me 4 )] ( 2 ) proves the fulvene-like structure of the uncoordinated tetramethylated cyclo -C 5 -moiety.

Colloidal synthesis of monodisperse luminescent InP nanocrystals

Luminescent InP nanocrystals were prepared by organometallic approaches using long chain alkylamines, trioctylphosphine and trioctylphosphine oxide as stabilizing and size regulating agents. The nanocrystals were characterized by powder XRD, synchrotron XPS, HRTEM, absorption and luminescence spectroscopy. Nearly monodisperse fractions of InP nanocrystals were isolated by the size-selective precipitation technique. As prepared, InP nanocrystals exhibit very poor photoluminescent properties, however, their PL efficiency can be drastically enhanced by photoetching of the nanoparticle surface with certain fluorine compounds. A new technique of controllable size-selective photoetching of colloidal nanoparticles allowed the preparation of nearly monodisperse fractions of InP nanocrystals with room temperature PL quantum yields of 25-40%. The PL band was tunable from green to near-IR with increasing particle size.