There are two identical crystals with the property of phosphorescing in the yellow part of the spectrum. Both crystals were preliminarily illuminated: the first with red rays, the second with purple rays. For which of the crystals can I observe the afterglow?
For the second crystal, it will be possible to observe the afterglow.
The wavelength of the exciting light should be less than the wavelength of phosphorescence light. Rays of violet have a shorter wavelength than yellow rays, and red rays have a longer wavelength.
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