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.
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:
- 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.
- Search the Internet with a combination of keywords such as phosphorescence, fluorescence, bioluminescence, minerals, rocks, chemicals. For example I may search for fluorescent minerals.
- 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.
- 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.
- 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.
- Search the Internet and call a local distributor of chemicals and science supplies to get price on the material that I need.
- Search the Internet and local stores to look for portable UV lights.
- Obtain the material that I need and perform my experiments.
Phosphor : A substance that exhibits phosphorescence.
Luminescence : The emission of light that does not derive energy from the temperature of the emitting body, as in phosphorescence, fluorescence, and bioluminescence. Luminescence is caused by chemical, biochemical, or crystallographic changes, the motions of subatomic particles, or radiation-induced excitation of an atomic system.
Compounds which emit light when excited electrically or by light–ie electrofluorescence, cathodofluorescence (excited by electrons instead of by a currrent), and photofluorescence. Fluorescent lamps are actually photofluorescent–the phosphors on the glass are excited by UV radiation from the ionized gas inside the tube, and emit visible light. CRTs and television screens are cathodofluorescent.
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.
Emissions applications have been under development since the 1960’s, in conjunction with the industrial availability of Rare Earths of sufficient purity. Such applications include television color, fluorescent lighting, and medical X-ray photography.
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.
|Use of Rare Earth Phosphors in Electronic Applications|
Y2O2S: Eu3+Gd2O2S: Tb3+
Red for television
Green for professional tubes
Y3 Al5 O12: Ce3+
Red corrector for high
pressure mercury vapor lamps
Sr5(PO4)3Cl: Eu2+LaPO4: Ce, Tb
(Ce, Tb) MgAl11O19
(Gd, Ce, Tb) MgB5O10Y2O3: Eu3+
Rare Earth Phosphors
Rare earth compounds are known to emit distinct and different wavelengths in the electromagnetic spectrum, the three main phosphor applications using rare earths are color cathode ray tubes, tri-phosphor fluorescent lamps, and x-ray intensifying screens, in which Y2O3 and Eu2O3 of 99.99% pure play a key role, in addition, high purity La2O3, CeO2 and Gd2O3 are used.
Rare Earth Elements
Because of their similarity, REE are difficult to separate and initial applications were based on “group” properties of a mixture of several of the elements. Thorium, along with associated REE, was first used in the 1800s in the manufacture of incandescent gas mantles. Other early uses of REE were in lighter flints, arc carbons, polishing compounds, and glass and ceramic additives. Mischmetal alloy, composed of 51-53% Ce, 22-25% La, 15-17% Nd, 3-4% Pr, 2-3% Sm, 3% Tb, 3% Y, and 5% Fe, is mainly used in the production of lighter flints and high-strength low-alloy steel.
Current uses of REE, summarised in Table 3, are about 95% in the mixed form, on a volume basis, with the individual elements accounting for the remaining 5%.
Major applications of the REE (Rare Earth Elements).
|Lanthanum||Component of mischmetal.||Ceramic glazes, high quality optical glass, camera lenses, microwave crystals, ceramic capacitors, glass polishing, petroleum cracking.|
|Cerium||Most abundant REE. Chief component of mischmetal.||Glass polishing, petroleum cracking catalysts, alloys – with iron for sparking flints for lighters, with aluminum, magnesium and steel for improving heat and strength properties, radiation shielding, many others.|
|Praseodymium||Yellow ceramic pigments, tiles, ceramic capacitors. With neodymium in combination for goggles to shield glass makers against sodium glare, Permanent magnets. Cryogenic refrigerant.|
|Neodymium||Important in magnetic alloys.||Ceramic capacitors, glazes and colored glass, lasers, high strength permanent magnets as neodymium-iron-boron alloy, petroleum cracking catalysts.|
||Not found in nature. Radioactive; produced only in nuclear reactors.||Radioactive promethium in batteries to power watches, guided missile instruments, etc, in harsh environments.|
|Samarium||Important in magnetic alloys.||In highly magnetic alloys for permanent magnet as Samarium-Cobalt alloy; probably will be superseded by neodymium. Glass lasers. Reactor control and neutron shielding.|
|Europium||One of rarest, and most rare reactive of rare earths. Absorbs neutrons.||Control rods in nuclear reactors. Colored lamps, cathode ray tubes. Red phosphor in color television tubes.|
|Gadolinium||Solid state lasers, constituent of computer memory chips, high temperature refractories, cryogenic refrigerants.|
|Terbium||Associated with gadolinium.||Cathode ray tubes, magnets, optical computer memories; future hard disk components; magnetostrictive alloys.|
|Dysprosium||Absorbs neutrons. Magnetic alloy.||Controls nuclear reactors. Alloyed with neodymium for permanent magnets. Catalysts.|
|Holmium||Absorbs neutrons.||Controls nuclear reactors; catalysts; refractories.|
|Erbium||Physical properties almost identical with Holmium and Dysprosium.||In ceramics to produce a pink glaze; infra-red absorbing glasses.|
|Thulium||Gives x-rays on irradiation in nuclear reactor.||X-ray source in portable X-ray machines.|
|Ytterbium||Properties very similar to Lutetium – not well known.||Practical values presently unknown. Research.|
|Lutetium||Chemical and physical properties not well known.||Deoxidiser in stainless steel production, rechargeable batteries, medical uses, red phosphors for color television, superconductors.|
|Yttrium||Associated with Holmium, Erbium. Cold or hot forged||Deoxidiser in stainless steel production, rechargeable batteries, medical uses, red phosphors for color television, superconductors.|
||Close to Aluminum in chemical and physical properties||X-ray tubes, catalysts for polymerization, hardened Ni-Cr super alloys, dental porcelain.|
|Thorium||Resembles nickel, as soft and as plentiful as lead. Radioactive.||Gas mantles. Can be used as nuclear fuel in place of uranium.|
|Cadmium Zinc Sulfide||Cd:ZnS||red|
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.
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.
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.
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:
- Calcium Oxide
- Barium Oxide
- Zinc Oxide
- Magnesium Oxide
- Cadmium sulfide
- 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.
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:
|Object or material name||Color on day light||Color under UV|
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.
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.
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)
These chemicals are expensive, so you are not really expected to purchase them. Of course if you want to purchase them, a local laboratory supplier is the best source. You may also try to find them and purchase them online. The way that I like is trying to get small free or inexpensive samples (1 to 5 grams) from a local chemist or a college. It will take a long time to gather samples of chemicals, but it is worth trying. I contacted a chemist working in a fluorescent bulb factory and got some samples. All my samples were blends and had no chemical name. I also burned some magnesium ribbon to make magnesium oxide for test.
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.
Under normal light, markings are not visible because they are the same color as paper. However under UV light, I was able to see three different colors.
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.
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.
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.
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.
List of References