What Is a Phototube?

Phototube is a basic photoelectric conversion device based on external photoelectric effect. Photocells can convert light signals into electrical signals. Photocells are divided into vacuum photocells and inflatable photocells. The typical structure of a photocell is to evacuate a spherical glass shell, apply a layer of photovoltaic material as a cathode on the inner hemisphere, and place a small spherical or small ring metal as the anode at the center of the sphere. If the ball is filled with low-pressure inert gas, it becomes an inflatable photocell. Photoelectrons collide with gas molecules during the process of flying to the anode to ionize the gas, which can increase the sensitivity of the photocell. The metals used as photocathode are alkali metals, mercury, gold, silver, etc., which can meet the needs of different wave bands. Photocells have low sensitivity, large volume, and are easily damaged. They have been replaced by solid-state optoelectronic devices.

Phototube

The principle of the photocell is

Vacuum photocells (also known as electronic photocells) are packaged in

Volt-ampere characteristics of photocells

Under a certain amount of light, the relationship between the voltage applied to the cathode of a photovoltaic device and the current generated by the anode is called the volt-ampere characteristic of the photocell.

Lighting characteristics of photocells

When the voltage applied between the cathode and anode of the photocell is constant, the relationship between the luminous flux and the photocurrent.

The slope of the illumination characteristic curve is called the sensitivity of the photocell.

1-oxycesium cathode; 2-antimony cesium cathode.

Spectral characteristics of photocells

In general, photocells with different photocathode materials have different red limit frequencies, so they can be used in different spectral ranges.

In addition, the same photocell has different sensitivity to light of different frequencies. Taking GD-4 photocell as an example, the cathode is made of antimony-cesium material, its red limit c = 700nm, and its sensitivity to incident light in the visible range is relatively high. It is suitable for white light source and is used in various photoelectric automatic detection instruments.

For infrared light sources, silver-oxygen-cesium cathodes are commonly used to form infrared detectors.

For ultraviolet light sources, an antimony cesium cathode and a magnesium cadmium cathode are commonly used.