Common fluorescent materials

What is fluorescence? A analogy could help understand that process which is very complex for people who have never done quantum physics.

Let's consider a ball that we let fall from some height h. The potential energy of the ball is mgh (where m is the mass of the ball and g = 9.8 m/s^2 is the earth gravitational constant) and because the ball as no kinetic energy initially, then the total energy of the ball is also mgh. When the ball bounce on the floor, it transfers part of its kinetic energy to the floor in the form of heat and vibration. So, since the total energy of the ball is not mgh anymore after the bounce, the ball wouldn't be able to go back to it's original height h, but instead at a lower height. The height at which the ball goes up to after the bounce depends on the properties of the ball and floor.

In a similar way, the light from a laser of a certain color that hit a material can change it's color, because the light transfers part of its energy to the material in the form of heat and vibration. The fact that the light change its color is in fact due to the fact that the color of light is directly connected to its energy (energy of the light absorbed by the eye or by a detector in a certain amount of time). For example, the energy of a red light is much lower than that of a blue light. In order of the less energetic to the most energetic color we have: red, orange, yellow, green, blue and violet. However, the energy of a certain light not only depend on its color, but also on its intensity. So, a blue light is only more energetic than a red light when the two lights have the same intensity.  We must first understand that light is in fact made of ''small ball'' that we call photons. The more photons by unit of time in a certain light, the more intense that light is and the more energetic that light is by unit of time. The energy of the light E is proportional to the number of photon N (when the number of photon is very very large) and to the frequency of the light v (which is connected to its color). The energy of a certain quantity of light is given by E=Nhv, where h is the Plank constant. However, when the light hit a material, yes that light can loss energy and therefore that light can change color, but each photon that hit the material doesn't change necessarily all to the same color. The graph of the number of photon of a certain color (frequency), after the collision with the material, in function of the frequency of these photons is call the fluorescence spectrum of the material. Each fluorescence spectrum of a specific material is unique and therefore we are able to find what is the material by studying the fluorescence spectrum of that material. Some material have a fluorescence spectrum that contains so few photons that we say that those material are not fluorescent, the others are said to be fluorescent.

Now let's look a some fluorescent materials that I discovered with my violet laser:

Here, we have the fluorescence of a hospital bracelet in the green when it's illuminated by a violet laser (405 nm). The laser beam don't seem violet, because the wood that was behind the bracelet was fluorescent in the blue. The picture is a long exposure, which explain why we see the laser beam trajectory:

Fluorescence of some post-it under a 405 nm laser. Again, it's a long exposure picture:

Fluorescence of a clothes hanger in the orange when it was illuminated by a 405 nm laser. In the second image, we see the full spectrum of that fluorescence. We can then see that the fluorescence is not only in the orange, but also in the red and the green. The spectrum as been obtained with a transmission diffraction grating:

Fluorescence of tree post-it and it's corresponding full spectrum. The first post-it is green, the second is light pink and the last dark pink:

Fluorescence in the yellow of used oil in a beaker when that oil is illuminated by a green laser (532 nm). We see the reflection of the green laser below the beaker, because the beaker act like a transparent mirror here. That oil is used in the vacuum pumps of our laboratory.

I was surprised when I shined my violet laser (405 nm) to a tree in the night. I realized that the tree was shining green after the laser was closed! The tree was phosphorescent! The part that was shining green is circled in red in the next picture which was taken in picture the day after:

Which seem to be a specific lichen. The lichen is also fluorescent in the green when illuminated by a 405 nm laser:

Being a physics student, I decided to do a emission spectrum of that fluorescence. We can se here the laser around 405 nm and the fluorescence around 520 nm and 555 nm.

I still don't know the lichen species name.