CALIFORNIA STATE SCIENCE FAIR
2016 PROJECT SUMMARY
Ap2/16
Name(s) Project Number
Project Title
Abstract
Summary Statement
Help Received
Hao Yang He
Quantum Physics and Glow in the Dark: Observing Luminescent
Radiation in Glow in the Dark Materials (Phosphorescence)
S1708
Objectives/Goals
The objective of this experiment was to determine if the brightness of light affect the luminescence of
phosphors? And which phosphor (Zinc Sulfide or Strontium Aluminate) would emit brighter light, persist
longer, and how do they differ?
Methods/Materials
Phosphors(Strontium Aluminate and Zinc Sulfide), light sensor, LED flashlight, Logger/Lab Pro hardware
& software(online sourced, obtained from teacher), and wood & cardboard for experiment setup. Exposed
respective phosphors to LED light for 10 seconds and measured resulting phosphorescence on light sensor
for 400 seconds in dark conditions. Brightness of the LED input light was changed between 480 lux, 300
lux, and 130 lux and tested on the phosphors.
Results
The average was taken for the initial t=0 luminescent value and the time it took for the phosphor to no
longer shine. The brightness of input light is proportional to the initial luminescence and persistence of
each phosphor. Strontium Aluminate emits more light and persists than Zinc Sulfide but only at high input
brightness(480 lux). Zinc Sulfide is consistent in light emission and persistence but does not perform as
well as Strontium Aluminate at high input brightness.
Conclusions/Discussion
The performance of the phosphors is consistent with electrons in atomic energy levels which absorb light
energy and releasing photons as they drop down energy levels. The persistence of phosphors indicate an
electronic state that holds electrons within energy levels for longer periods of time. The experiment also
shows differences in performance between Strontium Aluminate and Zinc Sulfide. Strontium Aluminate
requires a high brightness threshold to perform adequately whereas Zinc Sulfide requires a low threshold
and then is consistent throughout. Such difference can be caused by the phosphor's manufacturing process
and other elements it was mixed with.
I exposed two different glow in the dark materials (phosphors) to different levels of light brightness and
observed trends in initial brightness, brightness over time, and its emission persistence.
I designed the experiment myself but had some help from my dad constructing the setup. I also got advice
from my chemistry teachers.
