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FROM CURRENT LITERATURE
QUANTUM YIELDS AND SPECTRAL SENSITIVITY OF VARIOUS PHOTOCELLS
In connection with the extreme sharpness of the selective maximum of the spectral characteristic of antimony–cesium photocathodes¹, the question arose of determining the quantum yield for them. It was determined by a relative method by Luk’yanov² and then by Gurevich³, who made the same measurements also for other photocells. All these data are summarized in the table.
| Photocell | Quantum yield at maximum (%) | Integral sensitivity in μA/lm |
|---|---|---|
| Antimony–cesium (external photoeffect)² | ~ 33 25 |
100 |
| Silver–cesium–oxygen (external photoeffect)³ | 0.3 | 30 |
| Sulfur–potassium (external photoeffect)³ | 2.0 | 3 |
| Selenium (barrier-layer photoeffect)³ | 31 | 500 |
| Sulfur–thallium⁴ (barrier-layer photoeffect)³ | 39 | 5,000 |
From this table it is evident that at the present time there already exists a considerable number of photocells that are very sensitive indicators for different regions of the spectrum. Photocells with barrier layers are distinguished by especially high sensitivity.
It is of interest to compare the typical values of the integral sensitivity for the same photocells (in the case of the external photoeffect, vacuum photocells are meant). This comparison is also given in the table, where the sensitivity is referred to a source color temperature of 2,840° K.
Comparison of the tabulated data shows a significant discrepancy between the magnitude of the quantum yield and the integral sensitivity, which is a consequence of the position of the maxima on the spectral cha-
Spectral characteristics of these photocells are given in the figure, where the numbers standing by the curves correspond to those in the table. From these curves it is evident that, for almost any part of the visible spectrum and for the near infrared region, one can choose an element possessing high sensitivity in that region.
Figure: spectral sensitivity curves of photocells. Vertical axis: “Relative sensitivity”; horizontal axis: “Wavelength.” Curves numbered 1–5.
N. Khlebnikov
Literature
- N. S. Khlebnikov and N. S. Zaitsev, Uspekhi fizicheskikh nauk, 19, 736, 1938.
- S. L. Lyubimov, Zhurnal tekhnicheskoi fiziki, 9, 175, 1939.
- A. F. Gurevich, Zhurnal tekhnicheskoi fiziki, 10, 1940 (in press).
- See Uspekhi fizicheskikh nauk, 22, 110, 1939.