Gallium(III) oxide has been studied in the use of lasers, phosphors, and luminescent materials. Tetravalent manganese is used as an activator in red-emitting phosphors. Using different phosphors produces green and red light through fluorescence. However, several Mn activated fluorides were reported as potential red-emitting phosphors for warm-white LEDs. Gadolinium compounds are also used for making green phosphors for color TV tubes. Color tubes use three different phosphors which emit red, green, and blue light respectively. In the context of phosphors and scintillators, doping is better known as activation. Artificial willemite was used as the basis of first-generation fluorescent tube phosphors. For LCD monitors the pixel brightness changes are much slower than CRT or plasma phosphors. Every pixel is made up of three separate subpixel cells, each with different colored phosphors. Thermographic PIV is based on the use of thermographic phosphors as seeding particles. This also eliminated the need for cadmium phosphors in earlier color televisions. It is used as a feedstock for production of some phosphors and semiconductor materials. These lamps can produce much better quality light without resorting to phosphors. The lamp used a folded T4 tube, stable tri-color phosphors, and a mercury amalgam.