Speaker
Mr
ALI HALAKE WAKO
(University of the Freestate)
Description
1. Introduction
Long afterglow or persistent phosphors have the ability of absorbing energy from UV or sunlight and then release it slowly in the dark [1,2]. Inorganic phosphors doped with rare earth elements show broad band emission from blue to red which makes them suitable for a variety of industrial applications, such as luminescent pigments, fluorescent lamps, color display, plasma display panels (PDP), radiation dosimetry and X-ray imaging [3]. The type and duration of emission from a phosphor is affected by a number of parameters such as the type and amount of activators or dopants, the structure of the host lattice, the method of preparation or growth conditions and other post-treatments. These parameters play a significant role in inducing a crystal field effect within the host matrix which in turn influences the emission wavelength, its intensity and lifetime. The main task would therefore be to optimize these factors to obtain a phosphor that gives the best performance for the desired application. In this study thin films of SrAl2O4:Eu2+, Dy3+ /Nd3+ were prepared using Pulsed Laser Deposition (PLD). The effect of varying argon gas pressure and substrate temperatures on the structure and photoluminescent (PL) properties of the SrAl2O4:Eu2+, Dy3+ /Nd3+ thin films were investigated.
2. Results
X-ray diffraction (XRD) patterns of the SrAl2O4:Eu2+, Dy3+ /Nd3+ phosphor thin films deposited on Si(100) in vacuum, 10, 20 and 30 mTorr argon partial pressure as compared with that of the as-prepared powder are shown in figure 1. The peaks fitted well with the powder and the JCPDS card number 74-0794 for the monoclinic SrAl2O4 of space group P1211 (4). It can be seen that with increasing the argon pressure the peaks in the (220) direction shifted to the lower 2-theta angles from 29.1o in vacuum to 27.9o in 30 mTorr argon partial pressure. Ar has a higher mass density and therefore tends to reflect lighter atoms in the plume more and these results in a film with big particles [4] which results in lattice expansion inducing crystal field effect in host lattice causing the XRD peak shift to lower angles. Figure 2 shows PL emission spectra recorded with He-Cd laser at excitation of 325 nm from SrAl2O4:Eu2+, Dy3+/Nd3+ thin films deposited under different argon atmospheres whereby emission peaks are observed to shift towards the higher wavelength side. Larger particles will cause lattice expansion and increase the crystal-field interaction of Eu2+ resulting in red shift.
At what level of studies are you currently? (Hons/MSc/PhD)
PhD
Please provide the name and email address of your supervisor.
Francis B dejene
dejenebf@qwa.ufs.ac.za
Are you currently a postgraduate student? (Yes/No)
Yes
Primary author
Mr
ALI HALAKE WAKO
(University of the Freestate)
Co-authors
Prof.
Francis dejene
(University of the Free State)
Prof.
Hendrik Swart
(University of the Free State)
