Tin nanoclusters obtained in potassium chloride by thermal annealing

Abstract

Tin nanoclusters were obtained in potassium chloride crystals following the electrolytic coloration of KCl:Sn 2+ and KCl: Sn 2+ +Ca 2+ crystals and thermal annealing at various temperatures and times. Electrolytic coloration of KCl:Sn 2+ crystals produces electronic centers inside of samples, presumably negative metal ions of tin. Optical absorption measurements were performed on as grown sample, colored and thermal annealed samples. The behavior of the samples with Sn colloids was compared with theoretical predictions according to Mie's theory. Tin nanoclusters in KCl exhibit an absorption band with a peak at 215 nm. The structure of the nanoclusters was studied by optical absorption and transmission electron microscopy means.1 Introduction Metallic nanoclusters show unusual properties, having neither the bulk material nor the constituting atoms characteristics, and this is linked to the special behaviours that the nanoparticles exhibit [1]. One way to obtain metallic nanoclusters is the conversion of negative metal ions in colloids. The existence of negative metal ions in alkali halide crystals was the subject of o series of papers. Their identification was based of various techniques of characterization, like optical absorption, electric conductivity or Electron Paramagnetic Resonance (EPR) measurements. The methods for obtaining such negative metal ions were various, starting with X-ray irradiation, additive or electrolytic coloration. So far, was demonstrated the existence of Pband even Sn - [6]. The change of the valence for heavy metal ions were also observed in CaF 2 : Pb 2+ crystals under X-ray irradiation at the temperatures over 300 K, where Pb 2+ ions are transformed into Pb + , Pb + -Pb 2+ and/or Pb 0 (2) centres [7]. The next step is the conversion in colloids of these negative ions, which appears in the whole range of temperatures, starting with 77 K up to 800 K. For the centers created at low temperature, a warm up until room temperature is enough to evidence different reactions between negative metal ions and the other defects. For the centers obtained over the room temperature, thermally annealing leads directly into metallic colloids [8][9][10][11]. In this paper we present for the first time the method of obtaining the nanoclusters of Sn in KCl crystals using step-by-step conversion of the defects produced during electrolytic coloration [12], presumably tin negative metal ions, followed by thermal annealing.