Preparation by wet chemical method and some of properties of ZnS and ZnS : Mn2 nano materials

Semiconductors nanoparticles have quantum size effects and non-linear optical characteristics as well as high quantum efficiency, making them next-generation materials that can be applied in various optoelectronic devices. Semiconductor nanoparticles have attracted much attention because of their novel electric and optical properties originating from surface and quantum confinement effects.
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Preparation by wet chemical method and some of properties of ZnS and ZnS : Mn2 nano materials Journal of Science of Hanoi National University of Education Natural sciences, Volume 52, Number 4, 2007, pp. 72- 76preparation by wet chemical method and some of properties of ZnS and ZnS : Mn2+ nano materials Tran Minh Thi, Nguyen Minh Thuy, Pham Kim Tuyen Faculty of Physics, Hanoi University of Education1 IntroductionsZinc sulphide (ZnS) is important II-VI semiconducting material with a wide direct bandgap of 3.65 eV in the bulk [1]. It has potential applications in optoelectronic devices suchas blue emitting diodes [2], electroluminescent devices and photovoltaic cells [3]. Semicon-ductors nanoparticles have quantum size effects and non-linear optical characteristics aswell as high quantum efficiency, making them next-generation materials that can be ap-plied in various optoelectronic devices. Semiconductor nanoparticles have attracted muchattention because of their novel electric and optical properties originating from surfaceand quantum confinement effects.Manganese- doped materials represent a class of phosphors that have already found theirway into applications. The transition within the 3d5 configuration of the divalent man-ganese ion (M n+2 ) has been studied extensively and its orange- yellow luminescence in ZnSis well documented. This luminescence was also observed in nanocrystalline ZnS : M n 2+ [4]and applications have already been suggested [5]. Different types of Mn2+ centers arepresent in nanocrystalline ZnS : M n2+ [6]. The orange luminescence originates from M n2+ions on Zn 2+ sites, where the M n2+ are tetrahedral coordinated by S 2− .Many articles have reported on factors influencing the quantum efficiency of nanoparticlesZnS : M n2+ [6,7]. The luminescence quantum efficiency is important for the potentialuse of nanocrystalline ZnS : M n2+ in light emitting devices where a high luminescencequantum efficiency is required.2 ExperimentalZnS and ZnS:MnS nanoparticles are prepared by wet-chemical method. This method wasused chemical substances Zn(CH3COO)2 .2H2 O, M n(CH3COO)2 .4H2 O and N a2 S.9H2 Oand mix CH3 OH : H2 O.Firstly, 0,1 molZn(CH3COO)2 .2H2 O was dissolved in the buffer acetate CH3 COOH(pH = 3.5), solution contained 0,1 mol N a2 S was added drop by drop in a reaction vessel.A level of pH plays an important role in the precipitate of ZnS and ZnS : M n 2+ . The72 Preparation by wet chemical methodreactions were happened as follows: Zn(CH3 COO)2 + N a2 S → ZnS ↓ +2CH3 COON a M n(CH3 COO)2 + N a2 S → M nS ↓ +2CH3 COON aThe theoretical calculation shows that pH = 3.5 may be choosen to make precipitate of ZnSand ZnS : M n2+ in the mixed solution, without precipitating of Zn(OH)2 . This solutionwas constantly mixed by a homogenny during the entire process. The precipitate wasseparated by centrifugation at 2500 rpm and rinsed by mixer CH3 OH : H2 O(1 : 1ratio)in several times. Then all the rinsed samples were dried in low pressure (10 mmHg) at40o C for 48 hours.The ZnS : M n2+ samples were produced with correlative concentration of M n2+ : 0.0at%; 0.25at%; 0.75at%; 1at%, 1.5at%; 2.5at%, by wet-chemical method.For an qualitative analysis of ZnS, we used optical measurement at pH = 6.0 and testsubstances of blue methylthimol with maximum absorb wavelength λ = 592nm.The results of analysis show that the content of ZnS in samples achieved > 97% of volumeThe structure and crystallinity were characterized and analyzed by X- ray diffraction(SIEMENS D5005). The photoluminescence spectra were recorded with a by fluorescencespectrophotometer HP340-LP370 using laser that has excitation wavelength 325nm, atroom temperature. Photoluminescence spectral range was chosen 360-880 nm. The averageparticle size was measured by scanning electron microscope (SEM)3 Results and discussion Figure 1 shows the XRD patterns of ZnS:Mn2+ powders with correlative concen-tration of Mn2+: 0.0 at %, 1.0 at%. The samples ZnS-M5 (0%) and ZnS-M13 (0%) wereequally concentration of M n2+ , but they are dried at different temperatures. 73 TRAN MINH THI, NGUYEN MINH THUY, PHAM KIM TUYEN Order Sample d (111) a (Ao) 1 ZnS M5 (0%) 3.110 5.387 2 ZnS M13 (0%) 3.104 5.376 3 ZnS:Mn 1% 3.098 5.366 Table1: Parameters d, a of samples ZnS M5 (0%), ZnS M13 (0%), ZnS:Mn1% We can see that ZnS nanoparticles present the sphalerite phase and they have goodcrystallinity. The locations, widths as well as intensities of the XRD peaks are nearly thesame for all samples. The table 1 shows the lattices of samples are slightly decreased andseemed invariable at different dried temperatures and concentration of M n2+ .The average crystalline sizes are calculated by the width of the XRD peak at (111) plane inthe light of Scherres equation . The average crystalline sizes of samples are about 25 nm. Figure 2 shows SEM images of ZnS : M n2+ sample (1at%M n 2+ ) . It is clear thatthe grains in sample are not uniform. The diameters of the grains are mainly distributedin the range of Figure 3 shows the room temperature ph ...