Homebrewed phototransistors - unijunction versions
You can get the effect of a phototransistor by putting a photodiode on the base of a BJT, and if you don't have a photodiode, any diode in an optically transparent case will do. All PN junctions exhibit a photocurrent effect to some degree. LEDs work quite well:







simulate this circuit &ndash; Schematic created using CircuitLab

Would this work with a UJT? I suppose if you file off the case you would get some photocurrent. I have no idea if it would be enough to get you over the peak region so you can make an oscillator, at least with practical light sources. If you try it, post your results as an answer!