Low Temperature Growth of CaTiO 3 : Pr Phosphor Thin Film on Flexible Substrate by Photo- induced Chemical Solution Proc
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Low Temperature Growth of CaTiO3: Pr Phosphor Thin Film on Flexible Substrate by Photo- induced Chemical Solution Process Tetsuo Tsuchiya, Tomohiko Nakajima, Kentaro Shinoda National Institute of Advanced Industrial Science and Technology (AIST),Tsukuba Central 5,㻌 1-1-1 Higashi Tsukuba, Ibaraki, 305-8565, Japan ABSTRACT Preparation of the CaTiO3:Pr (CTO:Pr) phosphor thin film on PET substrate was investigated by using the excimer laser-assisted metal organic decomposition(ELAMOD) and photo reaction of nano-particles (PRNP) process. The effects of the substrate material, starting materials, and UV sources on photoluminescence (PL) were investigated. By using the BaTiO3 (BTO) nanoparticles buffer layer and the CTO: Pr nano-particles as a starting material, CTO: Pr thin film on the PET substrate was successfully obtained by using the KrF laser and excimer lamp irradiation at 25oC. It was found that excimer lamp irradiation is effective for improving the PL of the films. INTRODUCTION In recent years, to decrease the power consumption of photo devices, a field emission and electrical luminescence devices have attracted much attention because of the direct luminescent principals. Pr doped calcium titanate compound (CTO;Pr) have been reported to be good phosphors that exhibit red emission at around 612 nm, which is ascribed to the 4f- 5d transition of the Pr3+ [1]. Recently, Takashima and coworkers reported that CTO: Pr thin film electroluminescent devices at the working voltage of 10 V were prepared by Plus Laser Deposition (PLD)[2]. For the low cost and light display and lighting, the preparation of the phosphor thin films on flexible substrate would be expected to be the key technology. However, processing temperature of the CTO: Pr thin film is more than 500oC [3-5], it is difficult to prepare the film on glass or organic substrate. In a previous report, we have developed the photo-induced chemical solution process such as excimer laser-assisted metal organic deposition (ELAMOD) [8, 9] and have successfully prepared CTO: Pr thin film on quartz substrate [10, 11]. However, the PL intensity of the film prepared at 250oC is found to be higher than that of the film prepared at room temperature. A crystal growth of the CTO: Pr thin film by using ELAMOD process was found to be strongly dependent on the substrate material’s physical properties. Therefore, in this paper, to prepare the CTO: Pr thin films, we investigated the effect of the buffer layer materials on the PL properties. Also we developed the photo reaction of nano-particles method (PRNP) [12, 13] by using excimer lamp for the preparation of the phosphor thin film on organic or glass substrates. EXPERIMENT The starting solution was prepared by mixing constituent metal 2-ethylhexanoate solutions diluted with toluene to obtain the required concentration and viscosity for spin coating. The molar ratios of Ca, Pr, and Ti in the coating solution were 0.997, 0.002, and 1.00, respectively. This solution was spin-coated onto the SiO2 or SrTiO3 (STO) substrates at 4000 rpm
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