The Influence of Traces-Elements on the Colour of Ruby and Sapphire

Abstract

The pure corundum which comprises aluminium oxide is colourless The geological environment contributes different substance in the process of forming crystal so that the resultant corundum is in different colour The relation between the colour and trace-elements in the ruby/sapphire was not fully explained Also a universal numerical system to defined colour is needed so that the colour of the gem could be state and compare with The purpose of the study is to find the relation of trace element concentration and the colour and also to establish a standard procedure which is practical in both academic and commercial field In this study we collected corundum samples vary in geological origin and colour A colour grading system which was developed by the Gem and Jewelry Institute of Thailand–Gem Testing Laboratory (GIT-GTL) was employed to identify the colour of samples (Atichat et al 2006) On the basis of grading results the colour of samples were defined in CIE 1976 L* u* v* colour space The lightness and the hue of each sample was defined The numerical expression of colour component described the colour precisely and scientifically The optical transmission/reflection spectrum of samples were obtained via UV-Visible-NIR Spectrophotometers The concentration of trace elements were measured via laser ablation-inductively coupled plasma-mass spectrometry Cr Fe Ti and V affected the colour of ruby and sapphire Visible light transmission spectrum was able to reveal the effect of trace elements on colour Cr is the premier contributor of the red hue in ruby and Ti enhanced red hue when Cr concentration was low (

Date of Award	2016 Sept 5
Original language	English
Supervisor	Hui-Chen Kung (Supervisor)