This is the third paper in our Light-Emitting Diodes series. The series aims to create a systematic library of LED-based materials and to provide the readers with the description of experiments and pedagogical treatment that would help their students construct, test, and apply physics concepts and mathematical relations. The first paper, published in the February 2014 issue of TPT,1 provided an overview of possible uses of LEDs in a physics course. The second paper2 discussed how one could help students learn the foundational aspects of LED physics through a scaffolded inquiry approach, specifically the ISLE cycle. The goals of this paper are to show how the activities described in our second paper help to deepen student understanding of physics and to broaden student knowledge by exploring new phenomena such as fluorescence. Activities described in this paper are suitable for advanced high school courses, introductory courses for physics and engineering majors, courses for prospective physics teachers, and professional development programs.

Topics
Light emitting diodes, Electric lamps, Measuring instruments, Electric currents, Chemical elements, Batteries, Educational assessment, Teaching, Libraries, Scholarly publishing
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The following are just examples of curriculum materials relevant to this issue:
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In our experiments we used the following OptoSupply LEDs: red OSHR511P, yellow OS5YKA511P, green OSPG511P, blue OSUB511P, and white OSPW511P.
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We used a Vernier emissions spectrometer.
9.
The videos of the experiments are available at http://youtu.be/E87ovkzTxUo and http://youtu.be/oPWcczSgxRE.
10.
Note: if we increased the voltage across the yellow LED cooled in liquid nitrogen above about 6 V, it suddenly flashed bright and burned due to voltage breakdown.
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13.
Notice that we used two yellow LEDs in series directly connected to the voltage source (4.5-V batteries). The goal of such arrangement is to keep constant voltage across the LED and thus help students see the pattern clearly. If the LED is connected to the voltage source in series with a resistor, the voltage across the LED will increase as the LED's temperature decreases. In this case it might happen that the LED will remain glowing brighter when immersed in liquid nitrogen, although the current through the LED will decrease.
14.
A similar sequence of activities called Great White LED, has been developed at Kansas State University as a part of Visual Quantum Mechanics material, http://web.phys.ksu.edu/vqm/VQMNextGen/App&ModelBuilding/greatwhiteled.pdf. GWL combines I–V curves and spectral measurements with computer simulations to gradually construct an explanation about how white LED works. Our approach is different as we use only experiments, provide more activities (original), and systematically follow the ISLE cycle.
15.
The activities described in this section can also be done with a magenta LED (sometimes called a pink LED). A magenta LED consists of a blue LED covered with a reddish fluorescent layer.
16.
Note that such white LEDs did exist for short time in the 1990s. However, instead of being wired internally these LEDs had external leads for each of the LEDs.
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18.
Demonstrations of the white LED principle using blue LEDs and fluorescent markers have been described before in
Masahiro
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2015
American Association of Physics Teachers
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