靑色 사파이어의 熱處理와 分光學的 特性

Heat treatment and UV-spectral characteristics of blue sapphires from Shangtung, China

For the blue sapphires from Santung, China, the color change before and after has been investigated by UV-Visible spectrophotometry method. The blue sapphires from Shantung show four groups of absorption bands: the bands A (374, 386 and 450 nm) being attributed to single Fe³⁺ ion, the band B (560, 579 and 704 nm) to Fe²⁺/Ti⁴⁺ pairs, the band C (~800 nm) to Fe²⁺/Fe³⁺ pairs, and the D (528 nm) to Ti³⁺ d-d transitions. From those UV-VIS characteristics the origin of blue color of the sapphires is confirmed to be attributed by the factors such as Fe²⁺/Fe³⁺ and Ti³⁺/Ti⁴⁺. The absorption spectra of natural blue sapphires before and after heat treatment show distintive features, comparing with those of sapphires from other localities: the bands of 689 nm and of Cr³⁺ are not recorded on the spectra of sapphires from Shantung. The band (492 nm), which resulted from Ti³⁺, is not shown and the intensity of the band 528 nm decreases after the heat treatment. Decoloration of ink-blue sapphires are found to be successful by heat treatment with the control of annealing and atmosphere. During the diffusion process the excess components of impurities contained originally in the host crystal were expelled to the surface of crystals, enhancing the transparency of the crystals noticeably.