Properties of Sm-doped CaNb2O6 thin films deposited by radio-frequency magnetron sputtering

Sm-doped CaNb2O6 (CaNb2O6:Sm) phosphor thin films were prepared by radio-frequency magnetron sputtering on sapphire substrates. The thin films were grown at several growth temperatures and subsequently annealed at 800 degrees C in air. The crystallinity, surface morphology, optical transmittance, and photoluminescence of the thin films were investigated by X-ray diffraction, scanning electron microscopy, ultraviolet-visible spectrophotometry, and fluorescence spectrophotometry, respectively. All of the thin films showed a main red emission radiated by the transition from the (4)G(5/2) excited state to the H-6(9/2) ground state of the Sm3+ ions and several weak bands under ultraviolet excitation with a 279 nm wavelength. The optimum growth temperature for depositing the high-quality CaNb2O6:Sm thin films, which was determined from the luminescence intensity, was found to be 400 degrees C, where the thin film exhibited an orthorhombic structure with a thickness of 370 nm, an average grain size of 220 nm, a band gap energy of 3.99 eV, and an average optical transmittance of 85.9%. These results indicate that the growth temperature plays an important role in controlling the emission intensity and optical band gap energy of CaNb2O6:Sm thin films.