Structural and optical properties of Co-doped HfO² multi-layer deposited by spray pyrolysis technique

The optical and structural properties of co-doped HfO₂ thin films with rare earth trivalent ions prepared by ultrasonic spray pyrolysis technique, are reported. An arrangement of multi-layer (Si-SiO₂-HfO₂:Eu³⁺-HfO₂:Tb³⁺-HfO₂:Tm³⁺-SiO₂) were deposited on silicon substrates at temperatures from 400 to 550°C, using acetyl acetonates as precursory reagents. A refractive index value of 2.1 was determined by spectral ellipsometry. The surface morphology was obtained by AFM measurements. For 50 to 550 nm thickness films, an average roughness value of ~56.8 A was obtained for different substrate temperatures and grown deposition times. EDS measurements showed the presence of hafnium, and rare earths dopants as elemental composition. XPS measurements demonstrated that hafnium and rare earths oxidation species are formed at hafnium dioxide thin films. Photoluminescence emission spectra of multi-layer structures present characteristic emission peaks associated with Tb+3, Eu³⁺, and Tm³⁺ dopants. The results presented above motivate us to consider that these multilayer structures could be appropriate to be used as a rare earth host to improve optical emission.