Pulsed Laser Deposited Oxide Green Emitting Thin Film Phosphors : Optimization of Growth Conditions
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Pulsed Laser Deposited Oxide Green Emitting Thin Film Phosphors : Optimization of Growth Conditions P. Thiyagarajan1, M. Kottaismay2, and M. S. Ramachandra Rao2 1 Physics, Indian Institute of Technology Madras, Departmemt of Physics and MAterials Science Research centre, Chennai, 600 036, India 2 Indian Institute of Technology Madras, Chennai, 600 036, India Abstract Structural and photoluminescence (PL) properties of Zn2(1-x)MnxSiO4 (1 ≤ x ≤ 5) and diffuse reflectance spectroscopy (DRS) and morphological studies of ZnGa2O4:Mn thin film green emitting phosphors grown using pulsed laser deposition (PLD) technique have been investigated. Zn2(1-x)MnxSiO4 thin films grown on Si substrate at 700ºC in 300 mTorr of oxygen partial pressure, upon ex-situ annealing at higher temperatures exhibit superior PL intensity. ZnGa2O4:Mn phosphor thin films grown on quartz substrate at 650oC and in-situ annealed in 300mTorr of oxygen partial pressure show better emission intensity. For both Zn2SiO4:Mn and ZnGa2O4:Mn phosphors, luminescence can be assigned to 4T1 – 6A1 transition of Mn2+ within the 3d orbital giving rise to emission at 525 and 503 nm, respectively. Introduction Oxide phosphors are gaining importance in recent years over sulfide phosphors due to their chemical and thermal stability. Oxide phosphors find potential applications in light emitting diodes (LEDs), field emission displays (FED), plasma display panels (PDP) and X-ray imaging scintillators1. Among all the known oxide phosphors, Zn2SiO4:Mn is an efficient and a potential green emitting phosphor that has been widely used in PDP, cathode ray tube (CRT), fluorescent lamps (FL) and electroluminescent (EL) devices due to its high luminescence efficiency, chemical stability and high saturated colour index2. However, there are no detailed studies available on thin film growth of zinc silicate material owing to its refractory nature. ZnGa2O4:Mn (spinel structure) oxide phosphor in thin film form is considered as a promising luminescent material used in field emission displays and electroluminescent devices3. Mn doped ZnGa2O4 has been investigated for low-voltage cathodoluminescent green emitting phosphor4, where the luminescent center Mn2+ ions (activators) occupies the tetrahedral sites of the crystal lattice. Cr or Co activated ZnGa2O4 phosphors show reddish orange or red emission5,6. Luminescence from ZnGa2O4:Mn has been assigned to 4T1 – 6A1 transition of Mn2+ within the 3d orbital giving rise to emission between 501-506 nm7,9. In this work, we have optimized the growth conditions during the pulsed laser deposition of Zn2SiO4:Mn and ZnGa2O4:Mn thin films using various oxygen partial pressures (O2pp) on various substrates, respectively. Structural and luminescence properties of the thin films are reported and discussed in detail. Experimental (a) Target preparation: Mn activated Zn2SiO4 powder was prepared using combustion method, employing zinc nitrate hexahydrate, manganese acetate, urea and tetraethoxysilane (TEOS) in ethanol.
The manganese concentr
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