doi:10.1038/nindia.2015.25 Published online 20 February 2015
By heating nitrates of metals in the presence of organic fuels, researchers have synthesized glowing nanomaterials1. These nanomaterials are known as nanophosphors, and they exhibit a long afterglow when excited by ambient light. Nanophosphors are potentially useful as light sources for use in extremely dark conditions.
Nanophosphors show excellent chemical stability over a long time, and they have the ability to store and emit energy. These properties make nanophosphors suitable for use in luminescent paints, inks and sensors. However, scientists have been unable to find suitable raw materials (fuels), which has hindered the production of nanophosphors with desired properties.
The researchers synthesized the nanophosphors by heating the nitrates of strontium, aluminium, europium and dysprosium in an auto-combustion process by using fuels such as urea, citric acid, glycine and the carbohydrates lactose, dextrose and fructose. They then investigated whether the nanophosphors exhibited photoluminescence and a long afterglow when excited with light of different wavelengths between the near-ultraviolet and visible regions.
The researchers found that all the nanophosphors exhibited afterglow when excited with ultraviolet light for 15 minutes. Of the produced nanophosphors, those made with glycine fuel showed the best luminescence properties having the longest afterglow of almost 12 hours.
This afterglow was produced by the green luminescence from the nanophosphors made using glycine. Such emission happens when specific ions in luminescent materials are excited to high energy states by absorbing light and then drop to a lower energy state by emitting light. The researchers say that a similar phenomenon caused the metal ions in the nanophosphors to give off green light.
1. Swati, G. et al. Investigation on luminescence enhancement and decay characteristics of long afterglow nanophosphors for dark-vision display applications. Appl. Surf. Sci. (2015) doi: 10.1016/j.apsusc.2015.01.135