Study of various phosphors in fluorescent lighting

Introduction: (Initial Observation)

In a guided tour to a zinc mine that is now converted to a museums, I had an exciting experience. At the end of one of the mine tunnels, the tour guide turned off the lights and turned on UV lights. Suddenly I saw thousands or millions of colorful luminescent spots on the rocks. Since the UV lights were barely visible, it seemed that rocks were emitting light.

Later in a dark corner of a science museum I saw a display with similar minerals. The display had a button, allowing you to switch the light from visible to UV for comparison.

After some more studies, I now know that fluorescent lights actually produce invisible U.V. or Ultra Violet lights. The white powder coated inside the lamp is the substance that become excited by UV light and produces visible light.

What I don’t know is what specific chemicals are fluorescent and what colors do they produce? In this project I will attempt to identify and obtain some fluorescent chemicals and use them to convert a UV light to a multi color fluorescent light.

Be careful in handling chemicals. All chemicals must be considered hazardous, until proven otherwise.

Information Gathering:

Find out about what you want to investigate. Prepare a research plan. Research plan is a list of tasks that you want to do as your research. Such plan may change after you gather some initial information. Read books, magazines or ask professionals who might know in order to learn about the subject of your research. Keep track of where you got your information from.

My Research Plan:

Following are a list of tasks that I want to do during my study:

1. 1. Check encyclopedia or online dictionaries such as dictionary.com to learn the exact meaning of terms such as phosphors, luminescent, fluorescent, phosphorescence and any other related term that I find during my study.
   2. Search the Internet with a combination of keywords such as phosphorescence, fluorescence, bioluminescence, minerals, rocks, chemicals. For example I may search for fluorescent minerals.
   3. Obtain a UV light from a local hardware store or sports shop or museum and then try to find fluorescent rocks in my backyard, local park, local shores, local creeks. I know that I have to do it in the darkness or have a black fabric or black box for quick observations. I have already checked with my local hardware store and know that UV lights are sold as black lights.
   4. Use the fluorescent powders that I collect to make paints and cover a UV light bulb with those paints to make a multi-color light bulb. I think I can mix such powders with wood glue to make fluorescent paint.

My Research Plan PART 2:

After gathering the information, I learned that I can use Zinc Sulfide, cadmium sulfide and … as fluorescent substances for test. However I don’t know where I can get them cheap. So I made the following as the part 2 of my research plan.

1. 1. Search the Internet and encyclopedia to find out the uses of such chemicals. Maybe some of these chemicals have other uses and other names and I might be able to buy them from a local hardware store, paint store or pharmacy.
   2. Search the Internet and call a local distributor of chemicals and science supplies to get price on the material that I need.
   3. Search the Internet and local stores to look for portable UV lights.
   4. Obtain the material that I need and perform my experiments.

Sample Information:

Following are samples of information that I gathered by searching the Internet. The virtual show of UV effect on fluorescent rock is the most realistic demonstration of fluorescence that I could find.

Collection of fluorescent minerals from Franklin and Sterling Hill, New Jersey,
under short-wave ultraviolet (left) and normal light (right).

While searching about fluorescent minerals, I found mineral.galleries.com with a list of minerals that are fluorescent under long wave and short wave UV.

The list shows the name of mineral, not their chemical name. you can follow up the links to see what are the chemicals in each type of mineral.

The same fluorescent minerals are classified in another page with images that shows the mineral, under normal light and UV light. (mouse over required)

The fluorescence properties of some minerals are also uses as key to identify such minerals. As you see in the pictures, most minerals are only partially fluorescent because minerals often are a combination of multiple chemicals.

You may also notice that none of the minerals are producing enough light to be acceptable for commercial use and manufacturing fluorescent lights.

Research has been done by many fluorescent light manufacturers and their suppliers to discover chemicals that produce more light when excited by UV radiation.

Such research has lead to identifying some rare earth elements that are more luminescent under UV radiation.

Currently most fluorescent powders used in fluorescent lights are sulfides, oxides or other compounds of rare earth elements such as Cerium, Neodymium, Europium, etc.

Fluorescent lamps: they consist of a sealed glass tube, coated on the inside with phosphors and filled with an inert gas and a small quantity of mercury. An electrical discharge within the tube excites the mercury atoms which emit radiation predominantly in the ultra violet. This UV radiation is converted to visible light by the phosphors. Fluorescent lamps are available with different diameters, inert gas fillings and phosphor coatings. The color properties of a fluorescent lamps are determined by the phosphors used to coat the inside of the tube. A mixture of phosphors is used to produce a white color appearance, but this can vary in color temperature depending on the relative proportions of the phosphors in the mixture. The phosphor mixture also determines the color rendering properties of the lamp. All fluorescent lamps require ballasts to provide appropriate electrical conditions for starting and control of the discharge.

The intense emissions and almost monochromatic tones obtained by diluting the Rare Earths based activators in the appropriate host networks (very often simple rare-earth compounds at 0.7 or 14 electrons ¦: yttrium, lanthanum, gadolinium et lutetium) are the primary reason for this development. They made it possible to meet the very specific criteria for use that traditional band emission phosphors could not satisfy. A great variety of emissions can be obtained, depending on the type of activator brought into play and the respective positions of the excited or fundamental energy levels.

• Color Television with Cathode Ray Tube (CRT)

In color television, where the image is reproduced by selective cathode excitation of three phosphors (blue, green and red) deposited on the internal face of the screen, yttrium oxysulfides activated with trivalent europium (Y2O2S: Eu3+) facilitated such a gain in the brilliance of red over ZnS: Ag (more than doubled it) that it has totally replaced it at about five times less the cost.

The exceptional performance of the rare-earth phosphors has also been used gainfully in a vast number of cathode tubes for professional application: color computer monitors, tubes for aviation use, projection television, etc.

Diodes emitting a wide spectrum of colors are now manufactured all over the world. diodes have a longer lifetime than other lamps, so their use is particularly prevalent wherever lighting maintenance is expensive.

Information from a Chemical Dictionary:

Zinc Sulfide: ZnS. Exists in two crystallin forms, alpha (wurtzite) and beta (sphalerite).

Properties: Yellowish-white powder, stable if kept dry, Alpha: special gravity 3.98, Beta: special gravity 4.102; changes to alpha form at 1020ºC; sublimes at 1180ºC.

Uses: Pigments; white and opaque glass; base for color; lakes; rubber; plastics; dyeing, phosphor in x-ray and television screens; luminous paints; fungicide.

Zinc Oxide: ZnO. Coarse white or grayish powder; odorless; bitter taste; greatest ultraviolet absorption of all commercial pigments, nontoxic as powder.

Uses: Pigment, accelerator activator, ointments, mold growth inhibitor in paints; ceramics; floor tiles; glass; feed additive; dietary supplement; cosmetics.

Cadmium Sulfide: CdS. Yellow or brown powder. Special gravity 4.82; melting point 1750ºC; insoluble in cold water.

Uses: Pigments and inks, ceramic glaze, pyrotechnics, phosphors, fluorescent screens; rectifiers; photoconductor in xerography; transistors; solar cells.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to study different phosphors used in fluorescent lighting. This study includes identifying minerals and chemicals that are being used or can be used as phosphor. In other words I will test different substances to see which one is fluorescent and what color does it produce.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

The Independent or manipulated variable for our research is the type of substance that we test for it’s florescent properties.

Dependent variable is the color of light emitted when the substance is under UV light.

Controlled variables are other experiment or environmental variables that may affect the results of our experiments. Controlled variables are temperature, type and strength of UV radiation.

Hypothesis:

Based on your gathered information, make an educated guess about what types of material may be fluorescent. Identifying variables is necessary before you can make a hypothesis.

I think when the zinc sulfide and zinc oxide are fluorescent, the sulfide and oxide of many other metals should be fluorescent as well. Specially many of sulfides and oxides of earth metals and rare earth metals will have some fluorescent properties. My hypothesis is based on may gathered information and sample formulas that I have found. I will test my hypothesis on chemicals such as:

1. 1. Calcium Oxide
   2. Barium Oxide
   3. Zinc Oxide
   4. Magnesium Oxide
   5. Cadmium sulfide
   6. Zinc sulfide

I chose the above chemicals for test because I think I can easily find them locally. I may change this list if I could not find some of the items. I will also test the items around the house to find fluorescent material.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Introduction: In this experiment you will try to find some fluorescent material at home.

Procedure: Turn off all the lights at night. Turn on your portable UV lamp. Carefully go through the objects in your room or your house. Keep the lamp a few inches away from the objects that you observe. Make a list of all objects that are fluorescent and emit visible light when excited by UV radiation. In your search for fluorescent material, include different papers, dollar bills, stamps, labels, plastics, medicine and dietary supplements, soaps and detergents, glasses, your hands and feet, bones. Record your observations in a table like this:

Fluorescent pigments may be combined with plastics, paper, fabric, glass and paint. Many labels are made of fluorescent paper or are printed with fluorescent ink.

I also noticed some medicine such as dietary supplements containing Zinc Oxide are fluorescent, however when placed next to a more active fluorescent object, their fluorescence is not noticeable.

Without UV light, a regular paper and a fluorescent paper look the same, however under UV light, we will notice a big difference.

Among the household material, Ajax brand bleach and corn oil were among fluorescent liquids.

The most interesting part of this experiment is when you discover fluorescent dirt and bacteria around the house, specially around the stove, sink and refrigerator. Such dirt and bacteria are not visible in day light.

Experiment 2:

Introduction: Discover fluorescent minerals. In this experiment you will try to find some fluorescent minerals.

Procedure: Collect rocks and sands from different places near your home. In a dark room observe the rocks under UV to see if any of the rocks in your area contain fluorescent material. With the help of an adult, you may expand your search to the nature and search the beach or a hiking trail or a local park or creek under the illumination of your portable UV light. In this way you will not have to bring in so many rocks for observation. You can make observation outside and just pickup any fluorescent rock that you may find.

Note that fluorescent minerals are rare and you may not find any in your area.

Experiment 3:

Introduction: In this experiment you will test certain chemicals to see if they are fluorescent or not. The varieties that you test depends on what you can find or have access to.

Procedure: Gather samples of oxides and sulfides of different metals. You may optionally include some phosphates and carbonates as well. View them in a dark room, under UV light.

Some of the chemicals that you may test are:

Zinc Sulfide, Zinc Oxide, Zinc silicate, Cadmium sulfide, barium sulfide, strontium sulfide, calcium sulfide, Strontium phosphate, calcium tungstate, calcium carbonate (limestone), calcium fluoride (fluorite). (Not all of the suggested chemicals are fluorescent)

Note that many of the fluorescent pigments used in televisions and gas discharge tubes (also known as fluorescent bulbs) are compounds or blends of more than one fluorescent substance. Compounding and blending can result different shades of fluorescent pigments with higher fluorescence properties.

Another point is that the color of produced light also depends on the type (or wave length) of UV light (see an example). Different UV lights are also known as UVA, UVB and UVC witth wave lengths as follows:

UVA 400 nm – 320 nm (known as black light)
UVB 320 nm – 290 nm
UVC 290 nm – 100 nm

The highest wave length is from UVA that is also known as black light and you can simply purchase it from hardware stores. (Portable version is available at MiniScience.com). UVB and UVC are more specialized, more expensive and can only be purchased from medical and scientific suppliers.

Final point is that the form of crystals also affect the color of emitted light. A special substance such as calcite (natural calcium carbonate) may be fluorescent in one form and not the other. (Click here to see some fluorescent minerals).

It seems that Zinc Sulfide and Zinc cadmium sulfide are the most widely used fluorescent chemicals and are often a main ingredient of fluorescent pigments. Since small amounts of Zinc Cadmium Sulfide is invisible to the naked eyes, US army used it to simulate the use of biological weapons.

Many of fluorescent chemicals are white or colorless under normal light, but they will emit a specific light under UV radiation. Artists have sued such chemicals and produced pictures that is one thing under normal light and different thing under UV light. Such chemicals have also been used as invisible ink for creating secret messages. You may purchase invisible fluorescent pigments from riskreactor.com.

I used 3 different fluorescent pigments and made fluorescent paints. I did that by mixing the fluorescent pigments (powder) with small amount of water and small amount of wood glue.

Then I used a brush and made 3 different marks on a regular (non fluorescent) paper.

I also used the same paints to paint different spots on the fluorescent bulb.

When the bulb is on, 3 different colors were visible, however the picture that I took is not showing the colors.

Materials and Equipment:

List of material depends on your final experiment design. You may extract the list from the experiment section.

When I searched the Internet for a place to buy Zinc Sulfide, I found the following website. http://www.2spi.com/catalog/chem/zinc-sulfide.shtml .

You may find more if you search yourself.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculations are required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

List of References

http://www.rhodia-ec.com/site_ec_us/electronics/page_luminescence.htm

http://www.metall.com.cn/re/intro/application.htm

http://www.wtec.org/loyola/displays/c5_s2.htm

http://www.wiley-vch.de/contents/ullmann/ull_10427.html

http://www.maxpages.com/durotest/Aquatinic_Aquarium_Lighting

http://www.stanfordmaterials.com/LPGRP.html

http://www.stanfordmaterials.com/LPRD.html

http://www.sylvania.com/pmc/chem/pflamps.htm

A Sample project related to fluorescence

The Vocabulary of Luminescence

http://www.uvlamp.com