Which description best defines fluorescence in gemstones?

• A. Emission of visible light after stimulation stops.
• B. Emission of visible light during stimulation by UV or X-ray radiation.
• C. Continuous emission after the stimulus ends.
• D. Absorption of light without emission.

Answer: (B)

Fluorescence is the emission of visible light that occurs while a gemstone is being stimulated by ultraviolet or X-ray radiation. When the gemstone absorbs the high-energy photons, electrons are raised to a higher energy level and then almost instantly drop back, releasing light in the visible range. The glow appears only while the excitation source is on and stops as soon as the UV or X-ray is removed, because the emission is tied to the ongoing excitation rather than to a lingering afterglow.

This differs from phenomena where the material continues to glow after the stimulus ends (phosphorescence) and from simply absorbing light without emitting any visible light. In fluorescence, the emission is prompt and coincides with the illumination.