Preparation and properties of solar-blind photomultiplier tube
Dang Xiangyu     
Electron Tube Department, Beijing Hamamatsu Photon Techniques INC., Langfang, Hebei 065001, China

Overview: The spectral response range of the solar-blind photomultiplier tube is in the ultraviolet band, and it is insensitive to the visible and infrared bands. Because of its solar blindness, it has been widely used in ultraviolet radiation detection, ultraviolet communication and atomic fluorescence analysis instruments. Atomic fluorescence spectrophotometer as an element analysis instrument can detect mercury, chromium, beryllium, arsenic, antimony, zinc and other metal and non-metallic elements. With the increasing demands of the state and people on food, medicine and environmental protection, the demand for atomic fluorescence spectrometer is increasing. The use of the solar-blind photomultiplier tube can reduce the flame noise and avoid the design of complex optical path and light shielding system, so it is an important photodetector used in atomic fluorescence spectrometer.

But at present, the solar blind photomultiplier tubes used in the atomic fluorescence spectrophotometer on the market basically rely on foreign imports. The domestic solar-blind photomultiplier tubes are not satisfactory to the output sensitivity and life. Therefore, it is significant to develop a solar-blind photomultiplier tube with high output sensitivity, long service life.

The main components of photomultiplier tubes are incident window, photocathode, multiplier system and anode. The window material limits the cut-off wavelength of the photomultiplier tube in the short-wave region. The transmittance of window material affects the spectral response sensitivity of photomultiplier tube in short wave region. In this paper, synthetic quartz is chosen as window material of photomultiplier tube according to practical application. The types of photocathode materials mainly limit the response wavelength in the long-wave region of the solar-blind photomultiplier tube. Generally, the sensitivity of Te-Cs cathode decreases when the wavelength is more than 320 nm. But the preparation process is closely related to the wavelength, and inappropriate preparation process will seriously affect the cut-off wavelength in the long-wave region. How to ensure high cathode sensitivity and control white light sensitivity is one of the key and difficult points. The secondary electron emission coefficient of the dynodes determines the gain of the photomultiplier tube. How to make a high gain and ensure a small dark current is the other difficulty.

This paper mainly introduces the exhaust process of solar-blind photomultiplier tube, and designs a special double light source oven. Using the special double light source oven, the white light sensitivity and ultraviolet sensitivity can be monitored in the exhaust process. Through the analysis of the photocurrent and dark current on the small current amplifier, the activation termination point can be accurately judged to ensure high sensitivity and high gain. And at the same time, it can also control the sensitivity of white light and dark current. We test the performance of the solar-blind photomultiplier tubes. Results show that it has good solar-blind characteristic, cut-off wavelength at 320 nm, and output sensitivity can reach 5x105 A/W (250 nm), and gain can reach 1.3x107, and life is more than 1000 h. The solar-blind photomultiplier tubes are evaluated by several domestic analytical instruments manufacturers, all feedback are very good.