Do HPHT diamonds show a stronger fluorescence reaction to shortwave UV or longwave UV?

• A. Longwave UV
• B. None
• C. Shortwave UV
• D. Both shortwave and longwave equally

Answer: (C)

This question tests how fluorescence in HPHT-treated diamonds responds to different UV wavelengths. HPHT treatment can create specific defects or color centers in the diamond lattice that readily emit visible light when excited by UV photons. Shortwave UV has higher-energy photons (around 254 nm) than longwave UV (around 365 nm), so these centers are more effectively excited by shortwave light. The result is typically a stronger fluorescence response, usually seen as a blue glow, with longwave UV producing a weaker or negligible emission in many cases. Some HPHT diamonds may show little to no fluorescence at all, but among those that do fluoresce, the response is generally stronger with shortwave UV. Therefore, the stronger fluorescence is observed under shortwave UV.