Experiments with Glow-in-the-Dark Toys: Kinetics of Doped ZnS Phosphorescence

Abstract

Many semiconductors exhibit the property of phosphorescence, the phenomenon whereby a material excited by visible or ultraviolet radiation glows (i.e., emits visible light) for a substantial time after the excitation source has been removed. Absorption of visible or ultraviolet radiation, from sunlight or room lights, causes excitation of electrons and produces nonequilibrium concentrations of electrons and holes in the solid. Light is emitted as the electrons recombine with the holes, a process that occurs at a rate dependent on the material and the temperature. One phosphorescent semiconductor commonly used in glow-in-the dark toys and emergency signs is copper-doped zinc sulfide (ZnS:Cu), a material that produces a yellow-green glow. We have found the study of this light emission to be a suitable introduction to kinetics and to semiconductors.

Determination of a Kinetic Law of Phosphorescence Decay Using a Conventional Photo Camera and Free Image Processing Software

“…It should be noted that, in most inexpensive glow-in-the-dark children’s toys, ZnS:Cu phosphor is employed as the luminescent additive. , This phosphor consists of ZnS crystals with admixtures of copper and gives a long-lasting green afterglow with λ max ∼ 520–530 nm. , The glow-in-the-dark object with the phosphorescence intensity shown in Figures – exhibits the afterglow of this particular characteristic color. The luminescence of the ZnS:Cu phosphor can be excited with blue light and occurs via the recombination mechanism, with the emission centers being Cu + ions. ,,,, Although the compressed hyperbola law is the most common among crystal phosphors, and the ZnS:Cu phosphor is of greater abundance, when performing this work one can easily find objects that obey the exponential law and contain a luminescent additive another than ZnS:Cu.…”

“…It should be noted that, in most inexpensive glow-in-thedark children's toys, ZnS:Cu phosphor is employed as the luminescent additive. 2,19 This phosphor consists of ZnS crystals with admixtures of copper and gives a long-lasting green afterglow with λ max ∼ 520−530 nm. 20,21 The glow-inthe-dark object with the phosphorescence intensity shown in Figures 2−4 exhibits the afterglow of this particular characteristic color.…”

“…The luminescence of the ZnS:Cu phosphor can be excited with blue light 21 and occurs via the recombination mechanism, with the emission centers being Cu + ions. 2,13,15,19,22 Although the compressed hyperbola law is the most common among crystal phosphors, and the ZnS:Cu phosphor is of greater abundance, when performing this work one can easily find objects that obey the exponential law and contain a luminescent additive another than ZnS:Cu. This laboratory work was performed by some students of the chemistry department of the Baku branch of M.V.…”

“…Investigation of the kinetics of phosphorescence decay is a useful learning task in studying the formal kinetics, and also properties of crystal phosphors. This Journal has published a number of articles devoted to the phosphorescence decay kinetics. − In all of them, the luminescence intensity was recorded using special scientific equipment such as spectrofluorometers − or gauges linked to electronic signal processing devices. − In this work, it is shown that a conventional digital photo camera can be successfully used for quantitative observation of phosphorescence emission intensity. Using ordinary glow-in-the-dark children’s toys as phosphorescent objects allows one to perform the study of phosphorescence decay kinetics completely at home as part of distance learning.…”

Introducing Manganese-Doped Lead Halide Perovskite Quantum Dots: A Simple Synthesis Illustrating Optoelectronic Properties of Semiconductors

“…7 Although doping has attracted increasing interest in the nanochemistry field, the concept is yet to be incorporated into undergraduate laboratories due to the complexity in synthesizing doped QDs. 8,9 Several chemistry undergraduate laboratory experiments pertaining to QDs have been developed, pioneered by Nordell and Winker. 10,11 Currently, the range of QDs in teaching laboratories includes PbS QDs, carbon QDs, and core−shell QDs, etc.…”