The "Essence" of Light

The "Essence" of light is written by Sallie, a student, for her Chemistry class.  This project contains images and information from sources besides myself.  A bibliography is at the end.  

Introduction

Fluorescence, phosphorescence, bioluminescence; the “escence” of light.  Through these different chemical phenomena, creatures, rocks, and clothing can emit light in a unique way.  Fluorescence is the reason that your bowling ball glows in cosmic bowling (5).  When you have a glow in the dark keychain, phosphorescence is at play.  Fireflies thrive by using bioluminescence for mating (6).  Light made by chemical reactions falls under the category of chemiluminescence.  Studying the chemistry involved within these phenomena has solved many of these awe-inspiring and light-emitting mysteries. 

Fluorescence and Phosphorescence

Phosphorescence and fluorescence are two processes that make objects glow.  Although they are different, many similarities become apparent when further studied.  They both appear mysterious because they emit more light than other objects next to them.  Fluorescent molecules use their unique properties to harnesses energy that other molecules cannot (8). Phosphorescence continues to emit light after the source of energy is removed (5).  

Fluorescence

In black light, some posters glow eerily.  This cool effect is due to fluorescence (5).  Fluorescence’s emission of light is due to the de-excitation of electrons. A form of energy such as thermal energy is applied.  The electrons in the molecules become excited and move up one or more energy levels.  The spin on the electron remains constant.  This new electron is very unstable and quickly emits a photon to return to ground state.  This photon is often at a wavelength we can see (8).  What makes a fluorescent object glow, however, is that the objects next to it do not have fluorescent properties.  A fluorescent molecule takes a thermal or other non-visible source of energy and re-emits it at a different wavelength visible to the eye.  Because a significant greater amount of light is being emitted by a fluorescent object than a non-fluorescent object, it appears to be glowing.  The fluorescent materials are able to take non-visible energy and use it to emit more light.  The non-fluorescent object can only emit the relatively small amount of visible light in the room (5). Harnessing non-visible energy, fluorescence is a way for an electron to emit light.

Uses of Fluorescence

Fluorescence is broadly used in the world today. The most common application of fluorescence is the use of this property in fluorescent light bulbs (5).  A fluorescent light bulb consists of an evacuated glass bulb containing mercury vapor (8).  It is coated on the inside with fluorescent powder.  These powders are known as phosphors and contain fluorescent elements such as apatite analog (Sr₅(PO₄)₃F), antimony, and rare earth metals (8).  In the bulb, short waved UV light is emitted (5). Voltage is applied to the light bulb and mercury becomes ionized to conduct electricity.  The electron of the mercury vapor escapes leaving a mercury ion.  The electron collides with the mercury gaseous atom, become excited, and emits this UV light (8).  The phosphors in the fluorescent powder absorb the energy and re-emit it as visible light.  This way of producing light wastes less energy because the light bulb does not become hot and does not waste its energy heating the world.  Fluorescent materials are also harnessed and implemented in bleach. In this way, laundry detergent companies can argue that their bleach is “whiter than white.”  These companies put fluorescers in their detergents in quantities of up to one per cent.  Clothing manufacturers make their clothing with fluorescers already in them.  In the bright sun, white shirts can harness the UV energy and become very white (5). Many people’s professions are mineral hunters.  Although this job sounds humorous, these skilled professionals search for valuable minerals especially ones with fluorescent properties.  They can use their mineral’s fluorescent properties to decipher the origins of the mineral.  Some diamonds are even fluorescent!  Although nowadays people regard fluorescence as an impurity in their diamonds, the green light that some diamonds produced under black light used to be regarded as highly precious (8).  More common uses of fluorescence include posters that glow in black light, cosmic bowling, and in forensic science to identify clues (5).  Fluorescence is extremely useful in many areas of our lives.  

History of Phosphorescence

Phosphorescence makes many things “glow in the dark.”  It puzzled many everyday people when it was first encountered.  Although it was first seen in the seventeenth century, it was only until the nineteenth century that it was carefully studied (8). Philipp Lenard developed the currently used model.  As a boy in Hungary, Lenard played with fluorescent materials.  Later, he moved on to attend a university and develop his model.  He tried to equate phosphorescence with fluorescence and noticed something that went against the current thinking.  He developed a new explanation and published it in his theory of electron excitation and luminescence.  His theory was published in 1902, but it was not until 1905, when Einstein developed the idea of photons, that Lenard’s theory could be explained.  Lenard went on to win the Nobel Prize for a topic related to phosphorescence (8). 

Phosphorescence

Phosphorescence is the gradual re-emission of light at a lower energy (8).  Glow-in-the-dark objects use phosphorescence in order to work.  It differs from fluorescence because it can continue to emit light long after the source is taken away (5).  When a source of energy is applied, within the object the electrons become excited and start to move into a higher energy state.  They change their spin and get stuck in a metastable condition; the electron is not returning to ground state because it thinks it is stable.  In this way, glow-in-the-dark things are “charged up.”  They can be freed from this state by thermal energy.  This energy raises the electron to a higher level that makes it unstable and allows it to fall back to the ground state and release a photon.  This photon constitutes as the “glow” of the glow-in-the-dark object.  Because thermal energy is required to release the electron, phosphorescence is temperature dependent. The reason why the electrons are released so slowly is due to the changing spin of the electrons.  The decay of phosphorescence can vary from a fraction of a second to hours.  Phosphorescence saves the energy from its source and can continue to use it long after the source is removed (8).

Daily Uses of Phosphorescence

There are numerous uses for phosphorescence in daily life.  It is used in the theater to mark ledges and stairs.  When the lights go down for scene changes, the actors can still safely exit the stage.  Apart from glow in the dark toys, phosphorescence is used for more sophisticated needs.  Many watches are developed with phosphorescent materials on the hands so the user can tell the time in the dark.  The kinds of phosphorus that are commonly found in nature display this property hence the name, phosphorescence (8).  

Triboluminesence

Another way that atoms produce light is the process of triboluminescence. When you go into a very dark room and crunch on some mint Lifesavers, they create sparks in your mouth, but only if it is dry.  This occurrence is fun and due to triboluminescence. When you crunch the Lifesavers, they tend to break along planes splitting positively and negatively charged ions.  When one splits these sugar crystals, the ions try to bridge over the gap and create UV energy.  This energy is absorbed by the candy, which is fluorescent, and re-emitted as visible light.  This light is the spark one sees.  Triboluminescence is just fluorescence in disguise (5). 

Chemiluminescence

            Chemiluminescence is a general process that consists of a reaction that produces molecules that become excited and release light.  Some reactions that might have fluorescent or phosphorescent properties can also fall under the category of chemiluminescence.  This property is very broad.  All it involves is two molecules reacting to produce energy.  This energy excites the product of the reaction.  The excited molecule either releases a photon or transfers its energy to another molecule for emission.  Bioluminescence is a subcategory of chemiluminescence.  This process is how fireflies glow (7).

  One of the earliest studies of chemiluminescence was by Henry Brand.  This German alchemist was attempting to obtain gold from human urine.  Instead, he obtained phosphorous that glowed in the air.  This glowing was due to chemiluminescence.  Luminol is a chemical that is used in devices to measure nitrogen dioxide in the air.  Nitric oxide and ozone react together in a chemiluminescent reaction.

NO + O₃ = NO₂* + O₂

NO₂*= NO₂ + hv

In this reaction, nitric dioxide is produced in an exited state denoted by the asterisk.  This excited molecule emits a photon and completes the chemiluminescent reaction, which has about a ten percent yield.  This reaction was used in the 1970’s for detecting harmful nitric oxide exhaust in cars. Putting dry air through electric discharge easily creates ozone.  In these automobile tests, the sample exhaust and the ozone were mixed to create light.  This light was then amplified then measured.  The amplification allows for a broader range of samples of exhaust to be measured (7). 

            Glow sticks depend on chemiluminescence.  The U.S. Navy first developed them for stealth missions.  These sources of light are easily shielded if darkness is necessary. With this new technology, the U.S. Navy dropped behind enemy lines undercover.  Divers in murky waters also use these light sticks extensively (7). 

2H⁺ + C₂O₄^2- +H₂O₂ = 2CO₂ + 2H₂O

Hydrogen peroxide (H₂O₂) reacts with oxalate ester (C₂O₄^2- ) to produce two carbon dioxide (2CO₂) molecules, water, and energy.  This energy produced by the exothermic reactions is transferred to a fluorescent dye, which emits this energy as light.  The fluorescence makes the stick “glow.”  Another example of chemiluminescence at work is when metals glow blue when they get really hot.  However, the yellow flame from burning wood is not chemiluminescence.  Chemiluminescence is present in blacksmith’s shops all the way to the great depths of the ocean (7).  

Introduction to Bioluminescence

Bioluminescent Bay, or Biobay, is an anomaly of the world.  It is here, in Puerto Rico, that bioluminescence can be easily viewed.  This bay has 720,000 bioluminescent organisms per gallon of water!  These creatures are responsible for lighting up Biobay at night.  This picture below is just one of the fantastic sights that bioluminescence provides. 

The motion of the kayak is triggering the creatures in the water into lighting up and giving a bioluminescent show (10).  But what is bioluminescence?  Bioluminescence is the emission of light by organisms.  This process is a sub-category of chemiluminescence.  These creatures carry out a chemical reaction in their bodies.  The intermediate products of this reaction are excited and then emit light (8).  The Harbor Branch Oceanographic Institute found that between the depths of 200 to 1,000 meters, over ninety percent of organisms living there utilize bioluminescence (7).  While fluorescence and phosphorescence just re-emit light at different wavelengths, bioluminescence produces the excited molecule without external energy as a factor.  These three processes are comparable because their emission spectrums are similar.  However, fluorescence and phosphorescence occurs in organisms too, but they are not the same as bioluminescence (4).  

Big Picture Bioluminescence

Bioluminescence is a type of chemiluminescence that occurs in living organisms (4).  Many organisms use this process for mating, schooling, camouflage, and hunting (8).  These luminescent species lurk in marine habitats, in the air, and as terrestrial bacteria.  Many marine sea creatures use bioluminescence.  Some groups of animals, however, do not have any luminescent species.  These groups include mammals, vertebras (not including fish), higher plants, and viruses.  In labs, scientists have created luminescent versions of these animal groups by recombinant technology (4).  Some scientists believe that the some species are able to be luminescent by eating other luminescent organisms (4).

            On a larger scale, the reaction in bioluminescence is simple.  A chemical substrate called luciferin, when catalyzed by luciferase, reacts with oxygen to produce oxyluciferin in an exited state.  This product of the exothermic reaction is excited and releases a photon, or light!  This reaction occurs in many sea creatures.  Some of the key components are naturally produced in the organism or ingested.  This basic reaction appears in variations across the many bioluminescent species (1).  

Key Components in Bioluminescence

While studying firefly tales, scientists have discovers that there are a few key components in bioluminescent reactions that cannot be missing.  Oxygen is one of the reactants that is needed to carry out a bioluminescent reaction (1).  Fireflies breathe in oxygen though it’s complex systems of air tubes in order to deliver this ingredient to their stomachs containing luciferin (6).  ATP (C₁₀H₁₆N₅O₁₃P₃), or adenosine triphosphate, is essential to a bioluminescent reaction (11).  It is fortunate that ATP is a key ingredient in a living organism.    It is imperative that luciferin is present the reaction (1).  The composition of luciferin in different creatures varies (1).  This ingredient is oxidized by the enzyme luciferase.  This enzyme kick starts the reaction by lowering the activation energy needed to start the reaction.  From organism to organism, the enzyme luciferase can also vary.  These ingredients are essential to making organisms glow by bioluminescence (4).  In many types of species, luciferin must be brought in freshly for the reaction to occur.  This process may happen by eating other luminescent creatures of producing luciferin within their body (1).  

How Bioluminescent Reactions Occur

There are two main ways that bioluminescent reactions can occur.  The first occurs when the ingredients are separate.  The organism introduces the missing components in order for the bioluminescent reaction to occur and produce light.  This is the most simplistic version of the reaction.  Fireflies are thought to emit light in this way.  In some special organisms, all the key components to the reaction are already present together in something called a photoprotein.  This molecule contains the luciferin, luciferase, oxygen, and ATP.  Certain ions, like calcium, trigger the molecule to mix the oxygen and luciferin and catalyze the reaction emitting light (1).  Below is a diagram of what is happening in the oxidation of luciferin (1).

  

(1).

History of Bioluminescence

Luminescence has been observed for a long time, but it is only until very recently that we have been able to explain what iss happening.  The ancient Greek and Chinese both recorded sighting of luminescence.   Aristotle wrote about organisms releasing light over two thousand years ago!  He said, “some things, though they are not in their nature fire, nor any species of fire, yet seem to produce light”(4).  One phenomenon that scientists attribute to bioluminescence is milky seas.  These very rare occurrences have been recorded by seamen for centuries.  A milky sea is a rare occurrence where part of the Ocean emits a whitish blue light.  These lights, which extend at times to forty miles, make the sea look milky.  The first satellite image was taken January 25, 1995.  This phenomenon still cannot be explained, but many scientists think that it is due to a high concentration of bioluminescent creatures.  They compare it to a red tide, where algae accumulate in large bunches.  In the novel Twenty Thousand Leagues Under the Sea the submarine passes through a milky sea.  The parallels between an actual milky sea and the “sea of milk” described in the book make researchers conclude that this occurrence in the book was based on someone’s real account (1).  Overall, the exact reason behind the occurrences of milky seas remains a mystery.  Bioluminescence has been seen for centuries, but just only recently studied in depth.  

Bioluminescence in Fireflies

Bioluminescent properties occur in many species of beetles and fireflies (4).  In these types of animals, luciferase catalyses the reaction of luciferin. The decarboxylation of luciferin in the presence of ATP forms into another form of luciferin.  This form of luciferin can finally react with the oxygen and emit light.  The diagram below is a visual representation of the reaction (4). 

(4).

First, the D-luciferin and the adenosine triphosphate are present together.  The D-luciferin uses up two of the adenosine triphosphate’s phosphates to form adenosine monophosphate. The new form of luciferin with AMP attached oxidizes with O₂ gas to form a new compound. The AMP breaks away leaving another compound.  Carbon dioxide (CO₂) separates leaving an excited molecule that emits a photon (4) (9).  The structure of luciferin in a firefly is C₁₃H₁₂N₂O₃S₂ (8).  A firefly stores both luciferin and luciferase in its sixth abdominal part.  Oxygen comes through its air pipes and reacts the reaction starts when these ingredients are mixed (6).  This reaction produces light that shines through fireflies’ stomachs.  There are two different theories that scientist follow on the fireflies’ ability to flash their lights.  Some believe that the fireflies regulate how much oxygen they intake, using oxygen as the limiting reagent in the reaction.  If there is not enough oxygen, the light cannot be produced.  Another theory is that fireflies have physical control over the production of light besides limiting the reactants.  They think that fireflies use neural control to start the reaction (6). Fireflies use their bioluminescence for mating.  It is remarkable that their ability to produce light requires little heat and is 96% efficient.  The fireflies waste nine times less energy than incandescent light bulbs (6).  Fireflies and beetles have a remarkable ability to produce light in an efficient manner. 

Bioluminescence in Dinoflagellates

Some species of dinoflagellates, or very simple algae, have bioluminescent properties (4).  They are responsible for waves lighting up in the dark, or the visible wake behind a boat at night.  Although these algae are very small, when grouped together they can light up bays, waves, seas.  Scientists speculate that they could be responsible for milky seas, or large areas of water that glow in the night (1).  These bioluminescent species of algae are responsible for the light on the surface of the ocean (4).  The intensity of the brightness of the ocean is directly related to the concentration of the dinoflagellates in the water (1).  Many of these creatures are stimulated to produce light via bioluminescence by motion produced by fish or boats.  This is the light one can see in the wake of ships (4).  Due to the high concentration of bioluminescent dinoflagellates in Bioluminescent Bay, this body of water displays intense and brilliant bioluminescent behavior.  When one scares fish in Biobay, a blue light illuminates their trail due to the movement of water (10).  These algae emit light centered at 470 nanometers producing a bluish green light (4). The reaction that occurs in bioluminescent algae is much more simple that fireflies (4). 

(4).

The luciferin in the structure of a tetrapyrrole in the presence of ATP is catalyzed by luciferase to react with O₂.  In this oxidation reaction, a new compound is formed.  Water is a product that is removed leaving an excited molecule that emits a photon (4).  The left over unexcited molecule is no longer useful and often disposed (1). These tiny but bioluminescent organisms are triggered to produce flashes of light by motion.  The motion of waves or small organisms like fish is enough to trigger these dinoflagellates (1).   Heat and pH affect the behavior of these species of algae.  At pH 8 the luciferase is isolated from the luciferin prohibiting a reaction, while at a more acidic pH of 6, bioluminescence occurs (1). Although these dinoflagellates are small, when grouped together they can emit a lot of light.  

Bioluminescence in Other Sea Creature

Many sea creatures use bioluminescence for hunting or avoiding predators.  The anglerfish, or the scary fish in Finding Nemo that lit up, is an example of a bioluminescent creature.  This fish uses bioluminescence to lure its pray close.  It is then able to attack and consume them.  Some squid change color to avoid predators.  This form of defense is made possible by bioluminescence.  During the day, when the squid lurks in deeper water, it emits blue lights to match the color of the water where it is.  The water has filtered all the other colors except blue; therefore the squid only produces that color. When night comes, the squid migrates up closer to the surface and turns green and blue to match the relatively unfiltered moonlight.  Most sea predators hunt by looking upwards to see shadows.  By counter-illuminating, the squid can match the intensity of light around it in order to erase its shadow.  The squid changes its color by minute differences in the water because predator’s eyes adjust to a certain intensity and they can notice small changes.  The squid knows what color to change by the temperature of the water.  The deeper they are, the colder it is, and the blue they have to be. Both the anglerfish and squid use bioluminescence for survival (1).  

Uses of Bioluminescence

There are many potential uses for bioluminescence; however it is very expensive to procure bioluminescent creatures. In a more simple way, lanterns are made in many places by crushed up fireflies (8). The potential for using bioluminescence is science and technology is great. Because ATP is found in all life, NASA has considered testing for life on other planets by trying to run a bioluminescent reaction with the planet sample by mixing the planet dust with luciferin, luciferase, and oxygen. If the reaction glowed, that would most likely mean ATP was present and there is a potential of life on that planet (6). In a similar manner, tuberculosis treatments can be tested. A sample of the TB virus and the antibiotic can be combined with a bioluminescent reaction without ATP. Once the luciferase is added, the researcher can see how well the treatment is working by the intensity of light. If a lot of ATP, and consequently a lot of the living virus, is still present, the sample will glow showing the researchers that their medicine is not working. The intensity of the glow will show how well it is working (6). This phenomenon will help with gene therapy by signaling active genes by the same process of testing for life on planets (6). Thanks to dinoflagellates, bioluminescence can be used to detect movement and the flow of particles. These organisms can be used as microscopic flow sensors because they light up when they move (2). These algae have been successfully used to study the flow of water around a dolphin and the dynamics in the way that it moves (2). In the developing of artificial hearts, dinoflagellates can be utilized. Scientists need to know if the blood is being too hard or soft in their new hearts. These extremes can cause many fatal diseases. These doctors can use bioluminescent algae to measure if the blood is being pumped gently enough (2). Bioluminescence can be used in future research and technology.

Conclusion

There are numerous ways an object or organism car emit light. As seen in fluorescence, something can absorb photons and re-emit them at a different wavelength. In this process, the energy that collides and excites the electron, that quickly moves down to ground state emitting that energy as visible light. Fluorescence is responsible for the glow in black light. In phosphorescence, the electron gets excited but is put in a metastable phase where the electron thinks it is stable. The electrons are gradually freed from this state and they emit a photon when falling back to ground state; they continue to emit light after the source of energy is removed allowing them to glow-in-the-dark. Triboluminescence gains its energy by breaking positive and negative ions apart and emitting the energy, that is trying to bridge the gap, as light (5). The process of producing light by a chemical reaction is chemiluminescence (7). One form of chemiluminescence is bioluminescence. As seen in many sea creatures, organisms can emit light by oxidizing the luciferin in their bodies and emit light (4). All these types of luminescence are the “escence” of light.

BIBLIOGRAPHY

BIBLIOGRAPHY

(sorry the format is wacky)


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(2) Jennings, Paige. “ Glow with the Flow.” Scripps Institution of Oceanography. 28 Apr.
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(5) Rohrig, Brian. “A Light of a Different Color.” ChemMatters Apr. 1999 : 4-6.

(6) Shelton, Heather. “Bioluminescence: Fireflies and the Future.” 4 Jan. 2008. Serendip.
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(8) World of Chemistry. Detroit: Gale, 2000.

(9) McConnell, Jane. Helpful Discussion. 21 May 2009.

(10) “Bioluminescent Bay.” Nov. 20 2008. Island Adventures Biobay Tours 21 May 2009
.

(11) "Glow stick." Wikipedia, The Free Encyclopedia. 16 May 2009, 07:22 UTC. 22 May
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