Spectroscopic Characteristics and Identification Significance of Pink Diamonds of Different Causation Types

Pink diamonds are primarily categorized into 3 types: natural, treated natural, and treated synthetic pink diamonds. The colouration of natural pink diamonds is predominantly associated with plastic deformation or NV centers.Those coloured by plastic deformation display a broad absorption band around 550 nm in the UV-Vis spectra, and could be type Ⅰ a or type Ⅱ a. Natural pink diamonds coloured by NV centers are usually type Ⅱ a and are relatively rare. The colours of treated synthetic pink diamonds are mainly induced by NV centers, and they mostly belong to type Ⅱ a+Ⅰ b with low isolated nitrogen content. Treated natural pink diamonds exhibit greater diversity in type and more complex colouration mechanisms, posing certain challenges for detection. Based on previous research, 8 representative pink diamond samples of different types were collected and analyzed using gemmological microscopy, infrared spectroscopy, UV-Vis spectroscopy, photoluminescence (PL) spectroscopy, and fluorescence imaging. The results indicated that: (1)Type Ⅰ a pink diamonds coloured by 550 nm absorption band are typically natural; (2)Type Ⅰ a pink diamonds coloured by NV centers are usually treated natural diamonds; (3) Type Ⅱ a natural pink diamonds coloured by 550 nm absorption band typically exhibit high-temperature unstable centers such as H4 center (496 nm) and GR1 center (741 nm) in PL spectra; (4)Type Ⅱ a natural pink diamonds coloured by NV centers, in addition to containing high-temperature unstable centers, show no absorption peaks related to irradiation and annealing (e.g., 1 450 cm^-1 and 9 287 cm^-1) in their infrared spectra. The spectroscopic characteristics and identification methodology summarized in this study provide a practical reference for laboratory analysis.