Photoemissive Yield of Cs3Sb Photocathode and Its Dependence on Temperature

Abstract

A method which allows measurements of the photoemissive quantum yield of a Cs3Sb cathode of a photomultiplier is described. The method consists of an accurate control of the photocathode polarization to separate its eventual effects from the dependence of the quantum yield on the temperature. Measurements thus performed on four 56AVP phototubes have been interpreted as an up-to-now unknown variation of the quantum yield due to the temperature. The measurements suggest that the Cs3Sb could exist in two states, one of which, never noticed before, is stable only below (260±2)°K (the transition temperature), and which moreover is very sensitive to the absorbed energy. This low temperature state has a low quantum yield (for whitish-blue light), which, depending on the absorbed energy, can be even five to seven times lower than the yield of the usual high temperature state of Cs3Sb.

Thermosensitive Discontinuities and Hystereses of the Photoemission of Alkali–Antimonide Cathodes at High Light Intensities

“…They established a model of a change in crystal structure and related a large numbcr of less explained results of Cs,Sb cathodes t o this model [17]. With respect to the differences in the time behaviour and the light intensities, a connection of our results to those of De' Munari [17] is not evident, but in our case we can exclude a relation of the jumps and of a change in crystal structure. The jumps were observed continuously a t temperatures betm ern 50 and 210 OK, while changes in the crystal structure occur a t definite temperatures.…”

“…The comparison of our results with those of De'Munari et al [17] shows some differences. De' Munari found a hysteresis by measuring the temperature dependence of the photoemission current a t constant intensity and spectral properties of light and a t constant geometry of illumination.…”

“…Such a trivial explanation was often used when fading of photoemission was observed [12]. Our results are an example that the simplest explanation must not be the best one to get an insight in reality; indeed we can exclude the influence of dark conductivity, what -apart from many other arguments -can be seen best from the independence of the absorption constant on the conditions of sublinearities and discontinuities of the [17]. The hystereses observed by Penning and Moubis are similar to ours with respect to the comparable order of magnitude of the photoemission currents a t which the discontinuities occur.…”

“…De' Munari found a hysteresis by measuring the temperature dependence of the photoemission current a t constant intensity and spectral properties of light and a t constant geometry of illumination. We also have measured such "temperature hystereses" but the differences are : The times of the jumps a t the discontinuities were in our cases between 1 and 1 0 m s for multialkali cathodes and 10 s for Cs,Sb, while De' Nunari et al [17] measured times of more than lo4 s. The intensities of our measurements were in excess of 101l photons/cm2 s and were characterized by a fading sublinearity of the J-I characteristics, while in [17] the light intensities were so small that a special method was necessary to detect the emission current. De' Nunari et al…”

“…The measurements of De' Munari et al [17] are restricted to very small emission currents, while our measurements are characterized by high light intensities where fading processes are characteristic. De' Munari et al concluded that their measurements can be related to a transition between different modifications of Cs,Sb cathode material.…”