Problem of UV LED (400 nm) as light sensor

Now I use LED as a light sensor but what I have faced one problem. When I use some LED colors e.g. pink (450 nm) or UV (400 nm), they don’t respond to the different light intensity. They give the same output voltage.

For example, I inputted 2.75 V or 3.6 V to the UV LED light source then the output voltage from the UV LED light sensor was the same at 6.60 V.

Is it because of my amplification unit or semiconductor material of UV LED or the plastic of the UV LED absorb the light?

Please give me some suggestions about this problem.

Some modern methods of constructing LEDs work by having a UV emitting LED and a phosphor that gives it the colour they want. So the trick of using them as a light detector will not work.

LEDs that use a material with a “band gap” equivalent to the emitted photons are the only sort you can use as a light detector.