Summary

In this lesson students will investigate the fluorescence of a variety of everyday items as well as prepared samples under a black light. Students will examine the concepts of absorption and subsequent emission of photons, as well as wavelength, frequency, and energy of electromagnetic radiation. As extension activities, students will learn about phosphorescence and research real-life applications of photoluminescence.

Grade Level

High and Middle School

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• HS-PS2-6: Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.
• HS-PS4-3: Evaluate the claims, evidence, and reasoning behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other.
• HS-PS4-4: Evaluate the validity and reliability of claims in published materials of the effects that different frequencies of electromagnetic radiation have when absorbed by matter.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Analyzing and Interpreting Data

Objectives

By the end of this lesson, students should be able to

• Identify a number of everyday items that will fluoresce under a black light.
• Explain the emission/absorption of photons of light.
• Describe what is happening to the electrons in atoms/molecules when fluorescence occurs.
• Differentiate between fluorescent objects and glow-in-the-dark objects using the terms fluorescence and phosphorescence.

Chemistry Topics

This lesson supports students’ understanding of

• Energy
• Electromagnetic radiation
• Frequency
• Wavelength
• Electrons
• Quantitative Chemistry
• Photon emission
• Photon absorption
• Fluorescence

Time

Teacher Preparation: 60-180 minutes

Lesson:

• Engage: 10-30 minutes
• Explore: 45-100 minutes
• Explain: 30-60 minutes
• Elaborate: 20-40 minutes (Optional extension activities: additional 20-12o minutes)
• Evaluate: 30-60 minutes

Materials

• Black light(s) (UV-A light bulb)
• Everyday items (teacher examples and items from students)
  • Lego bricks
  • White t-shirts
  • Cotton balls
  • Highlighters
  • Fluorescent pipe cleaners
  • Cosmetics
  • Fishing line
  • Postage stamps
  • The website Science Notes has a great list of everyday items that fluoresce visibly under a black light.
• Grocery store/pharmacy items:
  • Fluorescent paint
  • Antifreeze
  • Laundry detergent
  • Mr. Clean liquid cleaner
  • Irish Spring soap
  • Vaseline petroleum jelly
  • B12 vitamins
  • Alka-Seltzer
  • Tonic water (with quinine)
  • Rock salt
  • Turmeric spice
  • Olive oil
  • Canola oil
  • Honey
  • Ketchup
  • Milk
  • Bananas with spots (see photos)
• Other Item Suggestions:
  • Different denominations of money (see photo)
  • Passports
  • Driver’s license
  • Credit cards
  • Note: UV lights will show a different color security band for different denominations of bills. Reference this link for colors of bands.
• For each lab group:
  • 2 sets of note cards or white paper
  • 1 yellow (or pink) marker (Crayola suggested)
  • 1 yellow (or pink) highlighter marker (Office Depot brand highlighters seem to have the brightest intensity under the black light)
  • 1 set of highlighters (3-4 different colors)
  • A set of white objects such as:
    • Wood painted white
    • White cotton balL
    • Sample of white leather
    • Sample of white plastic
    • White metal

Safety

• Students should wear goggles.
• Students should not look directly at the black light bulb for a long duration of time.
• Teachers should use a black light bulb with rays in the UV-A portion of the spectrum and not simply a UV lamp, as UV bulbs with shorter wavelengths and higher energy (UV-B or UV-C) can be damaging to the eyes.
• Check safety, warning, and disposal labels on any grocery item, especially items like cleaners, vitamins, and antifreeze.

Teacher Notes

• Preparation: If you have only one black light, you will need to conduct this activity as a demo and perhaps complete only some of the Parts I-V. It is best if you can set up your light in a completely dark room. You can purchase black light keychains if you would like to set up more stations for students but cannot afford to purchase multiple full-sized lights.
• Even if you have multiple lights, you may want to set up Part I as a teacher demo and introduction. Then allow students to work in groups for Parts II-V. If you only have a few black lights, you could allow students to rotate through stations, if you have a space where other students could work in light. If you have only one light, you could arrange Parts II-V of this lab to take place while other students are working on independent classwork and perhaps have one group at a time rotate into a dark closet, where you can monitor at the door. If time constraints or material constraints are an issue, this lab is still effective with only Parts I, III, and IV.
• For Part I, prepare samples that you would like to share with your classes. Check with other teachers at your school to see if they might have rock samples, fluorescent dyes, scorpions, or other interesting items that fluoresce. Make a grocery run to pick up some everyday items to test. See Materials section for suggestions. Science Notes website also has a great list of items.
• For Part II, ask each student or team of students to bring an object from home to test for fluorescence. Approve all student items before allowing groups to begin testing in Part II; students may attempt to bring inappropriate glow-in-the-dark items such as condoms, so make sure to allow sufficient time for students to get their items approved.
• For Parts III and IV, obtain white paper strips or index cards. For Part III, a yellow marker and yellow highlighter are needed for each group. (You can compare an orange or pink marker to its same colored highlighter, as long as desired effect of non-glowing marker ink and glowing highlighter ink is achieved with your sets.) During the lab, you will ask students to write a word on white index cards (or white paper) using yellow marker versus yellow highlighter. I wrote “yellow marker” and “yellow highlighter,” which is not overly original but it helped me remember which sample was which. For Part IV, prepare more white paper strips or index cards and a set of colored highlighters (3-4 different colors) for each group. During the lab in Parts III and IV, students will observe which marker and highlighter colors “glow” under the black light and which colors don’t.
• Make sure to check your examples and chosen yellow marker, highlighters, etc. under the black light. Some highlighters will glow faintly under the black light and others do not glow at all. You may also find that some markers will also glow (like Crayola’s pink in some packages). Usually the blue highlighter does not glow so you can make the designation that not all highlighters are created equally. If you want to differentiate, give each group different brands of highlighters, with colors that glow in some brands and do not in others; then ask them to compare data. In order to make the distinction between yellow marker ink and yellow highlighter ink, I have found that Office Depot brand highlighters have the brightest highlighter ink with the most glow. I use Crayola markers as my regular marker brand.

• Part III can be used to compare pink colors instead of yellow with older Original Crayola pink markers and pink highlighters. Newer Color Max additives to Crayola markers have included some fluorescent dye components because the ink of newer pink Crayola markers fluoresces where older pink marker ink appears darker in visible light and does not fluoresce.
• For Part IV, I have found that blue and purple highlighters do not tend to glow and yellow highlighters always glow; fluorescence under a black light varies by brand for orange, green, and pink. From my experience and recent purchases, the Office Depot brand highlighters have the most intense glow under the black light; pink, orange, yellow, and green glow, but blue and purple do not glow. Bic Brite Liner highlighters glow in pink, orange and yellow, but not in green or blue. Sharpie highlighters glow in yellow, and green, but not in pink, orange, blue, or purple.
• For Part V, obtain and prepare samples of small, similarly-sized squares of different white objects: cotton cloth, white trash bag, white metal, etc. The goal here is to find some white samples that fluoresce and others that do not. You may want to conclude the lab portion of this activity with this part as a demo if you do not have enough samples for each group.

• Engage: Students are interested in black lights and “glowing” objects, so in my experience it has been easy to connect them with this topic. My school has a black-light pep rally around Halloween each year, so I would begin a classroom discussion by referencing this much-anticipated event.
• Give out Introduction and Pre-Lab portions of the lab for students to read and then begin the Engage discussion above or you can send these portions home with students to complete for homework after the discussion.
• I suggest introducing this lesson at the close of class and ending the Engage portion by asking students to each bring in one item to the next class that they want to test with a black light. I offer a prize to the most original item to encourage and inspire creativity! It’s also important to make sure students understand that their items must be school-appropriate and that the teacher must sign off on them before they can be tested.
• You may want to use Flinn Fluroescent Dyes Demo (free to use and download) as an optional Engage demonstration at this point. I recommend using this activity as a more involved way to introduce this lesson, before starting the Procedure section, or before the Analysis portion of the lab.
• Explore: This section covers the Procedure and Observation portions of the student lab handout. This investigation can be split into two days/class periods, where each day is introduced by showing students something new about fluorescence, such as the glowing strips in different bill denominations or other cool untested samples, like a scorpion or fluorescent minerals. Refer to the Procedure section of the student document for the specific layout.
• Explain: Students will complete the Calculations section, and use Background information provided, as well as information from The Chemistry of Highlighter Colors, from Compound Chemistry to complete the Analysis questions. Teachers may want to provide hard copies of the Compound Interest handout, or make the link easily accessible for students.
• Elaborate: Students will read the article “Let it Shine” about PPG’s glow-in-the-dark tools and complete the questions in the Extension portion of the lab, discuss possible extensions and real-life applications with the class. Teachers may want to provide hard copies of the article, or make the link easily accessible for students.
• For your reference, this website summarizes some of the major differences between fluorescence and phosphorescence. It mentions forbidden spin state transitions, so it may be a bit beyond the understanding of students.
• Optional Extension Activities:
• Flinn Fluroescent Dyes Demo (free to use and download)
  • I recommend using this demonstrations as an additional portion of the Engage section of this lesson if time allows. The activity involves observations under visible light and black light for aqueous solutions of fluorescein, rhodamine, and tonic water, and an ethanol solution of eosin Y.
  • Extension Activity 1
    • I recommend using this activity in the Elaborate section. Students can make fluorescent, phosphorescent bouncy balls or slime using borax and Elmer’s glue from grocery store and glow in the dark powder from Educational Innovations. Instructions can be found in the AACT resource Changing a Monomer to a Polymer.
  • Extension Activity 2
    • I recommend using this after discussing glow-in-the-dark items. Students create their own fluorescent and phosphorescent creations, tying in a few concepts on polymers and crosslinking. The instructions can be found on my polymer lesson website, just add in the glow powder or paint!
  • Extension Demonstration
    • I recommend using this in the Elaborate section. The experiment is based on this Scientific American article, which is described in more detail in Teacher Notes below.
• Evaluate: Students complete the assessment questions as individuals or in lab partner groups, at teacher’s discretion. For an alternative method, on the short answer questions, teacher could have discussions with each student group instead of asking them to write out answers to be graded. Answer key is provided as a downloadable document for teacher reference.