International Journal of Science and Research (IJSR) ISSN (Online): 2319-7064 Index Copernicus Value (2016): 79.57 | Impact Factor (2015): 6.391 Volume 6 Issue 11, November 2017 www.ijsr.net Licensed Under Creative Commons Attribution CC BY The Effect of Argon Pressure on the Photoluminescent Properties of Laser Ablated SrAl 2 O 4 :Eu 2+ , Dy 3+ Thin Films Patrick D. Nsimama Department of Science and Laboratory Technology, Dar es Salaam Institute of Technology, P. O Box 2958, Dar es Salaam, Tanzania Abstract: The morphological, elemental composition and Photoluminescence (PL) properties of laser ablated SrAl 2 O 4 :Eu 2+ , Dy 3+ thin films prepared at different Argon (Ar) pressures are reported. The Atomic Force Microscopy (AFM) and scanning electron microscopy (SEM) techniques were employed for the morphological data collection. The data for elemental composition were collected using the Energy Dispersive X-ray Spectrometer (EDS) and Fourier Transform Infra-Red (FTIR). The room temperature photoluminescence (PL) data collection was done by using Cary Eclipse fluorescence spectrophotometry. The films were excited by the UV light from the xenon lamp. The PL intensities of the films seem to vary proportionally with the Ar pressure, when other parameters are kept constant. The highest green emission PL peak for the films is at 526 nm wavelength, attributed to 4f 6 5d 1 → 4f 7 Eu 2+ transitions. AFM images with well defined grains are observed on the films deposited at higher Ar pressures. The EDS and FTIR elemental composition analysis reveals that that the films consist of elements and groups of SrAl 2 O 4 . Keywords: SrAl2O4:Eu2+, Dy3+, thin film, PL, AFM, SEM, FTIR, PLD 1. Introduction The long afterglow strontium aluminate doped with europium and dysprosium (SrAl 2 O 4 :Eu 2+ , Dy 3+ ) is among the highly studied phosphor as can be substantiated by a number of published works [1-6]. SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphor is preferably prepared in thin film forms due to the fact that thin film phosphors have several advantages over powders, such as higher lateral resolution from smaller grains, better thermal stability, reduced out gassing and better adhesion to solid substrates [7]. Among the techniques employed in preparing SrAl 2 O 4 :Eu 2+ , Dy 3+ , pulsed laser ablation has distinguished itself as the most reliable and versatile technique. This is in part due to the fact that laser interaction with reactive gases is relatively weak and the deposition pressure range is extremely large, therefore electrostatic problems such as those encountered with sputtering are avoided. Additionally, the techniques can be applied in the growth of meta-stable phases and artificial structures which are impossible to stabilize by conventional means of synthesis [8]. The ability to easily change the deposited material in situ is another unique advantage to PLD which has enabled the development of new materials, including meta-stable phases and artificial super lattices, as well as the fabrication of novel device structures [9]. The deposition atmosphere during the PLD process has a great influence to the properties of the pulsed laser ablated particles as reported elsewhere [1, 4]. Nsimama and his co- workers [1] compared the photoluminescent properties of pulsed ablated SrAl 2 O 4 :Eu 2+ , Dy 3+ thin films deposited by using oxygen, argon and vacuum deposition atmospheres. The gas pressures were fixed at 0.34 Torr and other parameters were kept constant. The film with best luminescence properties was the one deposited in the argon atmosphere. It is of great interest to investigate the changes of SrAl 2 O 4 :Eu 2+ , Dy 3+ properties with the argon pressure, so as to establish the optimum range of argon pressure for the best PL properties of SrAl 2 O 4 :Eu 2+ , Dy 3+ thin films. That can provide a wider understanding of the PLD process in the argon atmosphere. Nonetheless, there is limited literature on the influence of argon pressures on the properties of pulsed laser ablated SrAl 2 O 4 :Eu 2+ , Dy 3+ thin films. Ali and his co- workers [5] reported on the pulsed laser deposited SrAl 2 O 4 :Eu 2+ , Dy 3+ , Nd3+ thin films and investigated on the argon pressure and substrate temperature influences on the photoluminescent properties of the films. Only small ranges of substrate temperature [100-300 oC] and argon pressures [10-30 mTorr] were considered and the laser fluency was 0.2 Jcm-2. The highest PL emission was recorded by the film that was deposited at low temperature (100 oC) and intermediate argon pressure of 20 mTorr. In the current work, the changes of SrAl 2 O 4 :Eu 2+ , Dy 3+ PL properties with the argon pressure ranging from 0.2-0.9 Torr are reported. Other parameters were kept constant. The FTIR data for the brightest film is analyzed and discussed. 2. Materials and Methods Silicon (100) wafer substrates were cleaned in an acetone for 5 min, in an ultrasonic water bath and then in methanol for the same time duration. Commercially available SrAl 2 O 4 :Eu 2+ , Dy 3+ standard phosphor powders from phosphor technology (UK) were treated as reported elsewhere [1] before installing in the PLD system. The deposition chamber was pumped by a turbo molecular pump to a base pressure of 8 x 10-6 mbar before the system was backfilled with argon ambient gas (purity 99.99 %) with pressures of 0.2 Torr, 0.44 Torr and 0.9 Torr, while fixing other parameters. The Lambda Physic 248 nm excimer KrF laser was used to ablate the thin films. The number of pulses, laser fluency and repetition rate were fixed at 12000, 0.74 J cm-2 and 8 Hz respectively. The substrate temperature and target-laser distance were fixed at 400 oC and 50 cm respectively. The ablated area was 1 cm2 and the laser beam was focused using a 20 cm focal length quartz lens on a rotating target at 45 oC angle of incidence. A Shimadzu Paper ID: ART20178326 DOI: 10.21275/ART20178326 1632