title: Multicolor luminescence patterning by photoactivation of semiconductor nanoparticle films.
abstract: Indiscriminate adsorption of nanoparticles (NPs) significantly complicates the preparation of mesoscale NP patterns considered as enabling technology for many devices and processes. Instead of selected chemical functionalization of the substrate surface prior to the assembly of nanocolloids, the required optical properties - in our case, high quantum yield luminescence - are imparted to the layer-by-layer assembled films by spatially selected photoactivation. The films are made by sequential adsorption of a positively charged polyelectrolyte and a negatively charged CdSe/CdS aqueous dispersion with an initial quantum yield of 0.5-2%. The photoactivation process takes place in the presence of oxygen and may be accompanied by photoetching. A 50-500-fold increase in the luminescence intensity of CdSe/CdS citrate-stabilized particles (quantum yield 25-45%) after visible light illumination provides excellent pattern contrast. Micron scale luminescence patterns were produced from NPs of various CdSe core diameters with red, yellow, and green emission. It was also demonstrated that different emission colors such as orange and green can be combined in one image by taking advantage of spatially selective photoetching. The presented optical patterning technique significantly simplifies the preparation of luminescence patterns as compared to conventional methods. The high signal-to-noise ratio associated with it is essential for optical devices, information processing, and biophotonics. The most immediate use of this approach is expected in cryptography and cell monitoring.
authors.affiliation: Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.forename: Zhiyong
authors.initials: Z
authors.lastname: Tang
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Correa-Duarte
authors.forename: Luis M
authors.initials: LM
authors.lastname: Liz-Marzán
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Kotov
mesh_terms: D019187:Cadmium Compounds / Q000737:chemistry; D003116:Color; D008163:Luminescent Measurements; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D036103:Nanotechnology / Q000379:methods*; D055096:Optical Devices; D010316:Particle Size; D010777:Photochemistry; D018036:Selenium Compounds / Q000737:chemistry; D012666:Semiconductors; D013440:Sulfides / Q000737:chemistry
chemical_list: D019187:Cadmium Compounds; D018036:Selenium Compounds; D013440:Sulfides; C034939:cadmium sulfide; C058667:cadmium selenide