Alternating current light-emitting

Direct and Alternating Current Light-Emitting Devices Based on Pyridine-Containing Conjugated Polymers... 

SCALE Symmetrically Configured Alternating Current Light Emitting... 

Phase-modulation immunoassay measurements are made with sinusoidally modulated light. Since the emission is a forced response to the excitation, the emitted light has the same periodicity as the excitation. Due to the time lag between absorption and emission, the emission is delayed in comparison with the excitation. The time delay between the zero crossing of one period of the excitation and of the emission is measured as the phase angle (Figure 14.11). The emission is also demodulated, due to a decrease in the alternating current (AC) component of the AC to direct current (DC) ratio. 

The simplest electronic devices, such as diodes, light-emitting diodes, lasers, and photocells, have a single p-n junction. If we place, say, a p-type doped Si block in contact with n-typed doped Si block, electrons will normally flow from the n to the p regions but not vice versa. Thus, the p-n diode so created can be fitted with ohmic contacts to function as a rectifier of alternating current. Schottky junctions can act in this way to some degree even without deliberate creation of a p-n junction. 

The most versatile and convenient method to overcome flame emission applicable to all elements is the modulation of the light emitted by the hollow cathode. This can be accomplished by running the lamp on alternating current or by interrupting the light beam mechanically with a rotating disk. The photoelectric current from the photomultiplier tube is then amplified by an a.c. amplifier. The d.c. component of the output of the photomultiplier tube, deriving from the continuous flame emission. 

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