My research is on Lanthanides and to very slightly correct Borek's statement, Promethium (Pm), the 5th element in the lanthanide series, is naturally unavailable. It can only be artificially synthesized and is radioactive.By the way, look up to the ceiling in some building. If you see a fluorescent lamp or LED lamp, the chance is, there are f-block elements in it. Specifically, Ce, Eu, and Tb for fluorescent lamps, and Ce for LED lamps. (Just to note that these days, there are increasingly more "warm" fluorescent lamps and LED lamps, which the composing elements are different.) If you have a cellphone or iphone or whatever phone with a camera, there's a little yellowish device next to it that you can use it for flashlight. Most likely, it is made out of Ce:YAG on a blue emitting diode.
If I recall correctly, smoke detectors contain Americium (I forgot the specific isotope), a crucial element for the device to work. There are also depleted Uranium ammunition and armor plates. Neodymium is commonly used in lasers and magnets. Gadolinium compounds are used as an imaging agent for MRIs.
Basically, they are used everywhere.