Security devices and methods of authentication thereof

A security device comprising:

• a substrate;
• and
• a photoluminescent image disposed on or in the substrate, the photoluminescent image comprising at least two different visible light emitting photoluminescent quantum dot compositions, each arranged according to different respective photoluminescent sub-images, the at least two different visible light emitting photoluminescent quantum dot compositions having different emission spectra from one another, and the same or different excitation spectra, the at least two different visible light emitting photoluminescent quantum dot compositions thereby emitting different respective visible colours from one another when excited;
• wherein the respective photoluminescent sub-images are configured such that the photoluminescent image formed by the combination of the respective photoluminescent sub-images is multi-coloured, emitting different visible colours in different laterally offset parts thereof upon excitation of the at least two different visible light emitting photoluminescent quantum dot compositions;
• wherein at least a portion of the photoluminescent image overlaps an at least semi-transparent region of the substrate.

A security device comprising:

• a substrate;
• and
• a photoluminescent image disposed on or in the substrate, the photoluminescent image comprising at least two different visible light emitting photoluminescent quantum dot compositions, each arranged according to different respective photoluminescent sub-images, the at least two different visible light emitting photoluminescent quantum dot compositions having different excitation spectra from one another, and the same or different emission spectra;
• wherein the respective photoluminescent sub-images are each configured to define a different one of a set of image frames which, when excited sequentially, exhibit the photoluminescent image, which is animated.

A method of authenticating a security device, the security device comprising:

• a substrate;
• and
• a photoluminescent image disposed on or in the substrate, the photoluminescent image comprising at least two different visible light emitting photoluminescent quantum dot compositions, each arranged according to different respective photoluminescent sub-images, the at least two different visible light emitting photoluminescent quantum dot compositions having the same or different emission spectra from one another, and different excitation spectra;
• the method comprising the steps of:
• sequentially illuminating the photoluminescent image with light of different wavelengths, such that the at least two different visible light emitting photoluminescent quantum dot compositions are excited sequentially and the security device exhibits the photoluminescent sub-images sequentially.