Electroluminescent devices

Claim 2

An electroluminescent device suitable for use with the application of unidirectional electric fields comprising a piece of electroluminescent phosphor material of the kind having a localized region of high resistivity produced by forming, and means for applying across at least a part of said region a series of unidirectional voltage pulses, said pulses having pulse heights whose average for the series is significantly greater than the forming voltage for the piece and pulse lengths whose average for the series is a value operative to provide emission of light having a brightness corresponding to the upper part of the peak of the pulse response characteristic for the piece at said average pulse height.

Claim 3

An electroluminescent device as claimed in claim 1 including at least first, second, third and fourth regions of electroluminescent phosphor material of said kind having a localized region of high electrical resistivity produced by forming, at least first, second, third and fourth conductors, said first conductor being attached to a first part of said first region and to a first part of said second region, said second conductor being attached to a first part of said third region and to a first part of said fourth region, said third conductor being attached to a second part of said first region and to a second part of said third region, and said fourth conductor being attached to a second part of said second region and to a second part of said fourth region, and means for applying voltages between at least one pair belonging to the pairs consisting of the first conductor and the third conductor, the first conductor and the fourth conductor, the second conductor and the third conductor and the second conductor and the fourth conductor, said applied voltages being in the form of a series of unidirectional voltage pulses having said average pulse height for said first, second, third and fourth regions of electro-luminescent phosphor material and having said average pulse length for said first, second, third and fourth regions of electroluminescent material at said average pulse height.

Claim 4

An electroluminescent device as claimed in claim 2 wherein the means for applying voltages is operative to cause the voltage pulses applied between said first conductor and at least one conductor belonging to the pair consisting of said third conductor and said fourth conductor to be applied during the time intervals when the voltage pulses applied between said second conductor and at least one conductor belonging to the pair consisting of said third conductor and said fourth conductor are removed, and is operative to cause the voltage pulses applied between said second conductor and at least one conductor belonging to the pair consisting of said third conductor and, said fourth conductor to be applied during the time intervals when the voltage pulses applied between said first conductor and said at least one conductor belonging to the pair consisting of said third conductor and said fourth conductor are removed.

Claim 5

An electroluminescent device as claimed in claim 3 wherein the voltage pulses applied by the means for applying voltages consist of electrical potential pulses of one polarity applied to said first conductor and electrical potential pulses of the opposite polarity contemporaneously applied to said at least one conductor belonging to the pair consisting of said third conductor and said fourth conductor, and consist of electrical potential pulses of said one polarity applied to said second conductor and electrical potential pulses of said opposite polarity contemporaneously applied to said at least one conductor belonging to the pair consisting of said third conductor and said fourth conductor.

Claim 6

An electroluminescent device according to claim 4 wherein said means for applying voltages is operative to cause each of the electrical potential pulses aPplied to any one of said first, second, third and fourth conductors to be applied only after a period when the magnitude of the electrical potential of that one conductor has fallen to a low value compared with the magnitude of the last electrical potential pulse in the series applied to that one conductor.

Claim 7

An electroluminescent device as claimed in claim 2, and wherein said regions of electroluminescent phosphor material are arranged in rows and columns in a matrix formation and are part of an electroluminescent panel.

Claim 8

An electroluminescent device as claimed in claim 4, and wherein said regions of electroluminescent phosphor material are arranged in rows and columns in a matrix formation and are part of an electroluminescent panel.

Claim 9

An electroluminescent device according to claim 4 wherein the means for applying voltages includes at least one switching circuit for switching one of said first, second, third and fourth conductors between a condition in which the magnitude of the electrical potential of that one conductor is high and a condition in which the magnitude of the electrical potential of that one conductor is low, the switching circuit incorporating at least one switching transistor responsive to low voltage control signals.

Claim 10

An electroluminescent device as claimed in claim 1 and wherein said series of unidirectional voltage pulses has a duty cycle as hereinbefore defined of at most 1 percent.