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: RE x ) emit visible light, originating from the RE ions, by 238–257 nm ultraviolet light excitation; that is, blue & red emission from RE  = Pr 3+ , red from Sm 3+ , green from Tb 3+ , and blue and yellow from Dy 3+ . 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 °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 °C).