An improvement on the compensating method for measuring the rise and decay of luminescence

Abstract

The rise and decay ofluminescence has been investigated for some time by the use of different compensating methods [1,2 ]. These methods could be applied to exponential rise and decay processes, by producing the compensating exponential voltage by the charge and discharge of a condenser. These methods could be used to zdvantage if the time dependence of luminescence could be described by a single exponential process. Diff~culties were encountered, however, when the rise and decay cnrve could be described only by the superposition of several exponentials.As was shown in several papers, the luminescence emission spectrum of willemite was found to consist of severa] bands [3, 4] and its phosphorescence decay curve also contained several components [5] identical with the spectrum bands [6,7]. The graphical analysis of the different decay components is not convenient, therefore an electronic compensating method was developed [8 ].Ir is well known that in monomolecu]ar luminescence processes the brightness may be described by the following equations : I--~ I0(1-e-fl t) during the rise I --I0(1 --e-~ T) e -at during the decay.T being the time of excitation,/~ the constant of rise and av that of decay, the time t being measured from the beginning of rise, and of decay respectively; a and q are different. The method described in paper [8 ] is capable of compensating either the rise, or the decay curve only. The original apparatus was built for 4 exponential components, but the number of components is not limited.In a reeent improvement of our method the simultaneous compensation of the rise and decay curve was developed. The principle of operation is as follows :A square wave generator is controlling the excitation of the luminescent specimen (e. g. the screen of a cathode ray tube) and the compensating device. A multiplier phototube measures the brightness of the specimen by producing voltage pulses on its load resistance, and these are compensated by the pulses of the compensating device.