Glow-in-the-Dark Materials

Why did I pick this topic for my project?

Ever since I was little, I have liked to see stars, and shining things, and lights in the dark. There are a few reasons: one is because they are glowing; the other reason is because I was afraid of the dark, so I had to sleep with a night light on. One day, I saw that there is a product called ``Glow in the Dark Stars.'' I was very happy to see it, because when the light is off, the whole room would be like a sky at night if the stars were all over the walls; and also I wouldn't have to turn on a night light when I sleep, because the stars are taking over the job of my night light.

For this WSE187 research cycle, Dr. Noe asked us to think of some topic to do for a project, and the night of the first meeting, I was looking at the stars on my wall. ``Why don't I just do a project on the stars, to find out how the glow-in-the-dark products work, what kind of environment makes the light last longer, and how much light intensity the stars hold in?'' Therefore, I chose this topic, and worked on it, which I found very interesting and matched to my interests. (I guess it's because this is a project I thought for myself, not some lab instruction with lab manuals.)

What is this project about?

This project is about phosphorescence, which is the technical term for the effect when a material emits ``glow'' light at a later time after having been exposed to light. The idea was to use a light detector to actually measure the intensity of the light emitted by a some phosphorescent (glow-in-the-dark) material as it steadily decreased over a period of time.

After searching on the web, a company in California called Shannon Luminous Materials was found that sells glow-in-the-dark materials. The company was contacted and the person there provided two very different samples to experiment with. One sample was labelled B-330, and was a copper-activated zinc sulphate. The second sample is B-901, which they said was "mixed oxides; containing, we think, Al, B, Sr, Eu, and possibly, Hf." The glow from the B-901 sample lasted much longer, so it was used for the measurement.

Setup of the experiment

The equipment used in the experiment was actually very simple and convenient:
The procedure was simple too .... The data was recorded in the voltmeter and stored in the computer, the we transfer the data type as a spread sheet format; looking at the correlation of the light intensity as the time passes when the samples were exposed under the flourescent light by the graphs obtained from the spreadsheet.

The diary and the analysis

The WSE187 ``Introduction to Research'' class meets twice a week for three weeks, and this cycle is repeated 4 times in the semester. My diary tells what we did in each class.

DAY 1:  First day of WISE research class. We were to asked to pick a topic and make some observations related to it, basically making a little experiment of our own. Dr. Noe talked about things like the index of refraction, light reflection, and the wavelength of light in different media. An interesting class, there were a lot of demonstrations presented. However, what should I do for this project? Maybe my "stars" on my wall which light up my room like the real stars all over the sky.

DAY 2:  My idea was approved by Dr. Noe, and samples were ordered from the company. Again, many demonstrations were presented since not everyone had thought about what they were going to do. We were also told that we were going to talk about our intended projects to the high school WISE students at the next meeting. First assignment was given also -- we were asked to write about our backgrounds and where we are from, and how we got into WISE.

DAY 3:  The high school WISE students came, we were talking about our backgrounds, and how we got into the WISE program, and how the college life is so far. We basically just introduced ourselves to the other WISE students -- it was mostly from the autobiography we wrote the other day. Everyone did a little demonstration of her project. A nice day filled with WISE people, and we had fun!

DAY 4:  Getting equipments for the experiment setups. Light detector, a dark environment, and samples (Came from the company in California few days ago). The dark environment was set up without light leaking in, as soon as the sample entered, which set the initail light intensity equals to 0. Two samples B-330 and B-901 were exposed under the flourescent light for about 5 minutes before they entered the dark environment.

As a result, it was found that the sample of B-330 can't hold light for a very long time. In othe words, as soon as it enters the black cover, the light decays enormously to almost completely no intensity contained in less than 5 second. However, the other sample, which is the B-901, holds light for a very long time. The first few seconds it also decays very fast, but after that the light decay slows down, and became steady. The sample can hold light for minutes and even few hours. It was a very amazing result. In this data recording, the light decays about 2 hours to approach to zero intensity.

*****Picture Gallery*****

Two Samples Demonstration of activating the samples Photocell in the detector Voltmeter close look
Complete setup The computer storing data and converting to spreadsheet format Experiement in progcess Comparision of the afterglow in two samples

DAY 5:  The fact that the sample B-901 was holding the light for a long time determined that it's the better example for experiment on light decaying. In fact, the light intensity dropped really fast for the first few seconds when it was taken into the black cover. It was the same effect as the sample B-330 did. However, one discovery was that, the B-330 sample didn't hold a high light intensity when it was exposed under the light. On the other hand, the B-901 sample was holding roughly twice as strong the B-330. That explains why the light dropped very quickly to almost disappearing for B-330 while the light was dropping yet it's still decaying in certain rate as soon as it passed the first few seconds.

DAY 6:  The data of the light intensity was recorded into the spreadsheet in the computer, we graphed it first with time and the voltage without taking log of the data. The graph showed an exponential dacay relationship between time and the light intensity. However, there were some gaps approach to the end of the lines, which are the 0's. It was probably the computer couldn't take more data, so it started all over again, but it was only about a second of data loss. It didn't effect too much since the decay was going extremely slow at that certain time spots.

We took the base 10 log for both light intensity and the time passed, a very interesting thing happened. The graph showed linear relationship between the two axes. We tried to traced the possible function of the graph, and finally, we found it may be the function of Y = 1/x for the line segment after time passes about 1 minute. This function may appear to be the power law function, which the general format for power law/log to log graph is y = kx^n, where k can be any constant, and n is the exponent for the function. in this graph, the constant is 1, and the exponent is -1. However, we can't conclude that the graph can be absolutely expressed in the poer law graph yet, because it's not a absolute straight line we are looking at.

There is another law that might be fit in to the graph, called Zipf's Law. Zipf's law is to express the probability of something's occurance is very high while some other thing 's occurance is very small. The graph for Zipf's Law is also a straight line with log-log graph, where the formal function is Pn ~ 1/ n^a: Pn is the probability of occurance for the Nth item, and a is exponent close to 1. However, after investigation, we found out that Zipf's Law is irrelavent to the graph we obtained, but it's a good reference of statistics.

It was very interesting that after thinking about the graph, and trying to find the relationship for a long time, it came out to be a function that looks so easy and simple. I thought it would be somethine even more complicated, but it's not a bad thing, and hopefully, it will make this project easier?!

My phosphorescence data

After this cycle of research....

It was very interesting that this project started nice and easy, and as I expected, there are much more out there for me to explore about this topic, which is also a fun thing to do. There are still so many different types of experiments I could work with this topic such as performing similar measurements with different wavelengths of light, or different temperatures. I will work on it later and experience the fun with this glow in the dark toys as far as it can get. Luckly, I got the chance to do my project even further, I am very happy about it. Maybe I will create something more interesting, it might be a glow in the dark cars, or glow in the dark chalk. Maybe a glow-in-the-dark roller coaster is also not a bad idea!! I think I will have much more fun soon!

I'd like to thank Dr. Noe from Laser Teaching Center who brought me this chance to work with such a fun thing, and taught me about doing research. It's a great experience I have had!

Some other cool links

There are some very interesting websites that Dr. Noe found, and I also found a few, to look at while I was doing this project and writing up this page. Here are the links for these, I hope you will enjoy them like I did:

If you have any suggestions or if you find any good websites that are related to my project, please E-mail to me, I will be happy to receive your e-mails. ^_^ Thanks

Email To Jill