X-ray absorption near-edge spectroscopy (XANES) can be used to study the oxidation state of a dilute system such as transition metal defects in solid-state samples. In blue sapphire, Fe and Ti are defects that cause the blue color. Inter-valence charge transfer (IVCT) between Fe²⁺ and Ti⁴⁺ has been proposed to describe the optical color's origin. However, the existence of divalent iron cations has not been thoroughly investigated. Fluorescent XANES is therefore employed to study K-edge absorptions of Fe and Ti cations in various blue sapphire samples including natural, synthetic, diffused and heat-treated sapphires. All the samples showed an Fe absorption edge at 7124 eV, corresponding to the Fe³⁺ state; and Ti at 4984 eV, corresponding to Ti⁴⁺. From these results, we propose Fe³⁺-Ti⁴⁺ mixed acceptor states located at 1.75 eV and 2.14 eV above the valence band of corundum, that correspond to 710 nm and 580 nm bands of UV–vis absorption spectra, to describe the cause of the color of blue sapphire.

Moisture content is an important quantity for agriculture product, especially in paddy. In principle, the moisture content can be measured by a gravimetric method which is a direct method. However, the gravimetric method is time-consuming. There are indirect methods such as resistance and capacitance methods. In this work, we developed an indirect method based on a 555 integrated circuit timer. The moisture content sensor was capacitive parallel plates using the dielectric constant property of the moisture. The instrument generated the output frequency that depended on the capacitance of the sensor. We fitted a linear relation between periods and moisture contents. The measurement results have a standard uncertainty of 1.23 % of the moisture content in the range of 14 % to 20 %.

Yellow color in gem corundum is commonly caused by Fe³⁺ impurity replacing Al³⁺ in the Al₂O₃ structure. For two decades beryllium-assisted heat treatment has been introduced to produce yellow sapphires from colorless, green, or light blue sapphires. The roles of beryllium atoms in corundum structure have been proposed in different ways either triggering structural defects or being as catalysts. Thus, the research experiments were conducted to evaluate these contradictions by applying the UV–vis excitation spectra and Fe K-edge x-ray absorption near edge structure spectra (XANES) of the samples, in combinations with Tauc plots of the UV–vis absorption spectra. The trace element content of the samples was analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). As a result, iron impurity in the samples has been confirmed as Fe³⁺ by XANES spectra, and hence, revealed as the cause of yellow color in natural yellow sapphire samples. Besides, the absorptions at 423 nm, 457 nm, 487 nm and 553 nm and emissions at 609 nm and 841 nm of Fe³⁺-Be²⁺ mixed donor states were detected by UV–vis excitation, which is the novel finding on the origin of yellow coloration in beryllium-treated sapphires. Therefore, an energy band model for mixed Fe³⁺-Be²⁺ donor states is proposed to be responsible for the yellow color center in beryllium-treated yellow sapphires, comparable to Fe³⁺ and Fe³⁺/Fe³⁺ states for the natural yellow sapphires commonly contain high iron.