Materials Chemistry and Physics 125 (2011) 342–346 Contents lists available at ScienceDirect Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys Photocatalytic effects for the TiO 2 -coated phosphor materials Jin-Ho Yoon a , Sang-Chul Jung b , Jung-Sik Kim a,∗ a Department of Materials Science and Engineering, The University of Seoul, 90 Jeonnong-dong, Tongdaemun-gu, Seoul 130-743, Republic of Korea b Department of Environmental Engineering, Sunchon National University, Chonnam 540-742, Republic of Korea article info Article history: Received 8 April 2010 Received in revised form 8 September 2010 Accepted 3 November 2010 Keywords: TiO2 Atomic layer deposition Photocatalyst CaAl2O4: Eu 2+ ,Nd 3+ abstract This study investigated the photocatalytic behavior of the coupling of TiO 2 with phosphorescent mate- rials. A TiO 2 thin film was deposited on CaAl 2 O 4 :Eu 2+ ,Nd 3+ phosphor particles by using atomic layer deposition (ALD), and its photocatalytic reaction was investigated by the photobleaching of an aque- ous solution of methylene-blue (MB) under visible light irradiation. To clarify the mechanism of the TiO 2 -phosphorescent materials, two different samples of TiO 2 -coated phosphor and TiO 2 –Al 2 O 3 -coated phosphor particles were prepared. The photocatalytic mechanisms of the ALD TiO 2 -coated phosphor powders were different from those of the pure TiO 2 and TiO 2 –Al 2 O 3 -coated phosphor. The absorbance in a solution of the ALD TiO 2 -coated phosphor decreased much faster than that of pure TiO 2 under vis- ible irradiation. In addition, the ALD TiO 2 -coated phosphor showed moderately higher photocatalytic degradation of MB solution than the TiO 2 –Al 2 O 3 -coated phosphor did. The TiO 2 -coated phosphorescent materials were characterized by transmission electron microscopy (TEM), Auger electron spectroscopy (AES) and X-ray photon spectroscopy (XPS). © 2010 Elsevier B.V. All rights reserved. 1. Introduction A titanium dioxide (TiO 2 ) photocatalyst has the potential to decompose various toxic gases and to oxidize various organic com- pounds, such as harmful dioxins, into harmless compounds such as CO 2 and H 2 O, by irradiation with UV light [1]. However, TiO 2 is a wide-bandgap semiconductor (3.03 eV for rutile and 3.18 eV for anatase) and can only absorb about 5% of sunlight in the UV region, which greatly limits its practical applications. Much research has been performed on the TiO 2 photocatalysts to improve their pho- tocatalytic reactivity and induce photoreactivity under visible light irradiation. The addition or doping of small amounts of noble metals, such as Pt, Rh, Pd, Ag, and Au, remarkably enhanced the photocatalytic reactivity of TiO 2 . The coupling of TiO 2 with other inorganic oxides, such as SiO 2 , SnO 2 , WO 3 , In 2 O 3 , (Sr,La)TiO 3+ı , and ZnFe 2 O 4 , changed the photocatalytic efficiency and the energy range of photoexcitation [2–7]. Metal-ion implantation with vari- ous transition-metal ions, such as V, Cr, Mn, Fe, and Ni, accelerated by high voltage, induced a shift in the absorption band of the titanium-oxide catalysts toward the visible-light region [8]. Eu 2+ -doped solid-state materials usually show strong broad- band luminescence with a short decay time in the order of some tens of nanoseconds. The characteristic broad band luminescence originates from transitions between the 8 S 7/2 (4f 7 ) ground state and the crystal field components of the 4f 6 5d 1 excited state config- ∗ Corresponding author. Tel.: +82 2 2210 2758; fax: +82 2 2215 5863. E-mail address: jskim@uos.ac.kr (J.-S. Kim). uration [9]. The luminescence is very strongly dependent on the host lattice and can occur from the ultraviolet to the red region of the electromagnetic spectrum. In addition to the initial very short decay time, the photoluminescence of Eu 2+ -doped alkaline earth aluminates, MAl 2 O 4 :Eu 2+ (M = Ca, Sr, Ba), also showed lumines- cence with a very long lifetime in the same characteristic blue/green visible range as the photoluminescence itself [10,11]. The long- lasting characteristics of alkaline-earth aluminate phosphors have attracted considerable attention for their potential applications in such fields as luminous paints, safety indicators in emergencies, electronic instrument dial pads, lighting apparatus and switches, automobile dials and panels, writing and printing inks, and plasma display phosphors. Up to now, alkaline-earth aluminate phosphors with excellent properties, such as blue CaAl 2 O 4 :(Eu 2+ ,Nd 3+ ), green SrAl 2 O 4 :(Eu 2+ ,Dy 3+ ) and BaAl 2 O 4 :(Eu 2+ ,Dy 3+ ), have been devel- oped for various applications [12,13]. Atomic layer deposition (ALD) techniques can be utilized to obtain atomic-layer-controlled growth of conformal thin films [14–16]. The ALD method relies on alternate pulsing of the pre- cursor gases and vapors onto the substrate surface and subsequent chemisorption or surface reaction of the precursors. ALD is achieved by repeating two separate self-limiting half reactions in an ABAB... sequence. In the case of the TiO 2 ALD reaction using the titanium tetraisopropoxide (TTIP, Ti(OCH(CH 3 ) 2 ) 4 ) and H 2 O, these two half- reactions can be written as (A) Ti(OH) x ∗ + Ti(OCH(CH 3 ) 2 ) 4 → Ti(O) x Ti(OCH(CH 3 ) 2 ) 4−x ∗ + x·CH(CH 3 ) 2 OH, (1) 0254-0584/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2010.11.004