Thallium(I) sulfide's electrical conductivity changes with exposure to infrared light therefore making this compound useful in photoresistors.[28] Thallium selenide has been used in a bolometer for infrared detection.[33] Doping selenium semiconductors with thallium improves their performance, and therefore it is used in trace amounts in selenium rectifiers.[28] Another application of thallium doping is the sodium iodide crystals in gamma radiation detection devices. In these, the sodium iodide crystals are doped with a small amount of thallium to improve their efficiency as scintillation generators.[34] Some of the electrodes in dissolved oxygen analyzers contain thallium.[2]