The Post Office

Aubrey Douglas Walker

Berkeley Michael Ferro

Rodney Edwin Spratling

David C Powell

An organic phosphor which is a solid insoluble in water and organic solvents and which may be used in a phosphorescent printing ink or a paper coating composition comprises molecules of at least one phosphorescent activator held within a matrix of a condensation resin that does not itself absorb ultraviolet or visible radiation at the excitation and emission frequencies of the phosphorescence activator(s). The phosphorescence activator(s) is/are a compound or mixtures of compounds of the general formula

Phosphorescent materials

A credential, such as a passport or an identification card, is provided, for example by impregnation or coating, with a phosphorescent composition which includes at least two phosphorescence activators which exhibit different emission characteristics both with respect to wavelength and lifetime so that, when the composition is irradiated, the initial afterglow changes color, for example from green to blue.

Identification matter

A method of rendering a surface, especially a paper surface, phosphorescent, in which a composition comprising a phosphorescence activator and a soluble condensation product of formaldehyde and an amino compound is applied to the surface and is allowed to react in situ to form a phosphorescent insoluble condensation product. The composition may, for example, be in the form of a printing ink or a paper-coating mix.

Phosphorescent materials and solutions suitable for their preparation, the solutions comprising a phosphorescence activator and a soluble condensation product capable of further reaction to form an insoluble condensation product, the latter being one that does not absorb ultraviolet radiation in the absorption range of the activator.

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North Harrow, United Kingdom

Aubrey Douglas Walker