Several rocks or minerals will glow under black light or ultraviolet light under certain frequencies of light emissions.
many crystal types like fluorites, some others like chromium in ruby, zirconium, tungstates, calcite, gypsums, manganese, or selenites,
I have only used light for finding brightly colored Fluorite ore crystals, n pretty glow in the light but almost as easily found in most any light, the rocks already stick out like sore thumbs, and the fluorite crystals are mostly for the wife's nik-nak shelf or maybe a little powdered for a flux additive.
I do not see any relation to gold, although gold also reflects certain frequencies of light.
gold can be thinned flat thin enough to see through the gold foil we only see green when looking through gold, used in arc welding glass shields, and other applications, gold also makes good laser mirrors,
They use gold as well as many other metals in medicines (or some medical poisons, or radioactive medicines...) Light in UV range to other frequencies such as X-ray and you name it in the medical or biological fields, that type of thing is what the images pictured above remind me of (biological or carbon-based chemistry, not much to do with gold in rocks.
I would forget the fancy flashlight and learn how to pan for gold if gold was my goal.
light will decompose some materials, can chemically, or can produce or cause electro-chemical reactions or effects, photography silver gold mercury, or some other halides or metal or chemicals salts reacting to light, as mentioned cyanide as well as nitric acid ...
very active metals sodium, potassium, cesium, and rubidium with exposure to radiant light frequencies can cause electrons to move or be removed, photoelectric and its effects...
Spectrography using light movement and splitting to determine elements... ...
Some crystals or rocks split light like the rocks the early sailors used to navigate to sail the oceans.
Gases like chlorine and others react to light... as well as chlorine or others in solution (pools for swimming or water treatment to kill germs or ultraviolet for aggravating or killing those little tiny biological critters...
I would also research the methods used before chasing my wild ideas ( although they do get me places), I can waste a lot of time running in circles...
Other things will react with metals or their salts and as well in chemical reactions like heat or cold, sound frequencies, vibration, magnetic fields, microwave or radio frequencies, and electricity, well I am just rambling now.
