X-ray induced luminescence, optical, compositional and structural investigations of natural and imitation rubies: Identification technique

In this work, the x-ray induced luminescence technique was used to investigate natural and imitation rubies. The red and pink natural rubies in the present work were provided from Myanmar and Vietnam, respectively. The imitation rubies (red and pink glasses) in glass were taken from imitation jewelry company in Thailand. Optical, compositional and structural were studies to confirm the identification of natural and imitation stone. X-ray diffraction (XRD) study reveals that natural rubies contain α-Al₂O₃ as the major phase. On the other hand, XRD does not show sharp peak for imitation ruby stone, therefore it indicates that the imitation rubies are made of amorphous material (glass). Absorption spectra in visible region of natural rubies, red and pink glasses show a prominent absorption band around 520–560 nm wavelength with Cr³⁺ transitions, gold nanoparticles and Er³⁺ transitions, respectively. Photoluminescence (PL) emission spectra of both natural rubies show strong red emission at 692 nm (λ_ex = 577 nm), relating to Cr³⁺ transition (²E_g→⁴A_2g). The green emission peak at 548 nm (λ_ex = 403 nm) of imitation ruby (pink glass) was observed; it comes from the transition of Er³⁺ (⁴S_3/2 → ⁴I_15/2). The x-ray induced luminescence (XIL) spectra of natural rubies show similar pattern with PL result, while XIL of imitation rubies cannot be observed. This XIL result show the fast separation behavior between natural and imitation rubies. Therefore, XIL is suitable for using as a luminescence analysis of gemstones because of their fast process, non-destructiveness and without excitation wavelength special sample-preparation needs.