Complex Nature of the UV and Visible Fluorescence of Colloidal ZnO Nanoparticles

Abstract

Time-resolved spectroscopy of colloidal ZnO nanoparticles has been carried out with a laser excitation at 248 nm. UV and visible fluorescence has been analyzed. Except for the known band gap 370-nm and impurity 510-nm emissions, we have found additional continua at ∼300, 430, and 545 nm. These continua were developed in solutions of different composition, with excess Zn and OH ions, and in function of time. All but 510-nm fluorescence bands exhibit short nanosecond or subnanosecond decays. The green fluorescence at 510 nm originating from 4-nm particles in Zn-rich solutions is a much longer-lived, 1.0 μs. The band natures are discussed. Cluster size distribution and growth kinetics have been recovered from spectral measurements.

Combined X-ray Diffraction and Diffuse Reflectance Analysis of Nanocrystalline Mixed Sn(II) and Sn(IV) Oxide Powders

“…At a given temperature, this region of the spectrum can be modeled with the empirical Urbach relation 38,39 where a0 and E0 are material parameters, hv is the photon energy, and Eu is the Urbach energy describing the width of the exponential absorption edge, which originates from the sub-band gap photon assisted optical transitions. 40 Absorbance of SnO2 in the Urbach tail region has been related to electrical responses in gas sensor testing 30 and the widths of the Urbach tails, Eu, have been shown to correlate with degree of crystallinity of SnO2. 29 Ultimately, the development and optimization of gas sensors based on mixed SnO2/SnO materials requires an understanding of the relationships between synthetic conditions and the formation of tin oxide phases, the effects of the mixed oxidation state on observed phase transitions and thermally induced grain size changes, as well as the characterization of the electrical/optical properties of these materials.…”

Polychromatic Source Excitable and Enhanced Green Photoluminescence of ZnO Nanoparticles Dispersed in High Molecular Weight

“…[10,11] This indicated that the dispersion of ZnO nanoparticles in polymer matrix stabilized the luminescence spectra of ZnO nanoparticles. This result has a significant technological implications such as for producing ZnO based fixed color displays or fluorescent biological labels.…”

“…However, the fresh colloid that exhibited a prominent PL peak at around 500 nm, suffered a significant red shift caused by increase in cluster size when aged over several days. [10,11] A shift from 500 nm to 560 nm was observed when the colloid is aged over a few days. [10] The excitation source wavelength must be carefully selected since the excitation spectra is very narrow, i.e., the width at half maximum (WHM) is only around 10 nm.…”

“…The production of ZnO colloid is similar to that reported elsewhere. [11] An amount of 4.39 g (CH3COO)2Zn•2H2O was put in 200 mL of ethanol and heated under stirring in distillation equipment at temperature of 80 o C to result about 120 mL of condensate and 80 mL of hygroscopic solution. The time required was around 3 hours.…”

“…The red shift indicated the decrease in the band gap opening as time increased, caused by a growing process of nanocrystallites. [9][10][11] By assuming the total spectra was a superposition of excitation spectra of individual particles and since the total spectra was very narrow, one expected the particle sizes were nearly monodisperse. Time dependence of excitation spectra of ZnO colloid detected at 500 nm.…”