Multiple Color Inorganic Thin-Film Phosphor, RE-Doped Amorphous Gallium Oxide (RE = Rare Earth: Pr, Sm, Tb, and Dy), Deposited at Room Temperature

Multi-color inorganic thin-film phosphors are deposited at room temperature on glass substrates using ultra-wide bandgap amorphous gallium oxide (a-GO) as a host material. All of the a-GO films doped with four kinds of rare-earth ions (a-GO:REx) emit visible light, originating from the RE ions, by 238-257 nm ultraviolet light excitation; that is, blue & red emission from RE = Pr3+, red from Sm3+, green from Tb3+, and blue and yellow from Dy3+. The a-GO:Pr-x and a-GO:Tb-x films emit bright light clearly visible by human eyes. Although the internal quantum efficiencies of unannealed a-GO:Pr-0.02 and a-GO:Tb-0.02 films are 0.2 and 1.8%, respectively, those are improved to 2.4 and 3.8 %, respectively, by post-deposition thermal annealing in O-2 at 400 degrees C through desorption of weakly-bonded oxygen and structural relaxation. On the other hand, the annealing temperature to improve photoluminescence is limited by crystallization (onset temperatures 400-500 degrees C).