Amphon, R. “GEMOLOGICAL AND SPECTROSCOPIC PROPERTIES OF BLUE SAPPHIRES FROM DEN CHAI DISTRICT, PHRAE PROVINCE”. Suranaree Journal of Science and Technology, vol. 23, no. 2, Aug. 2026, pp. 141-5, https://ph04.tci-thaijo.org/index.php/SUJST/article/view/14190.