EVOLUSI STRUKTUR DAN SIFAT OPTIK MATERIAL FOTOLUMINESENSI SELF-ACTIVATED NA2TISIO5 DENGAN INKORPORASI ION CA2+

• Main Author: Dian Ruhimat, Dzaky
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/72772
• Institution: Institut Teknologi Bandung

promising rare-earth free alternative material for light emitting diode (LED) component. However, its commercial application is limited due to the low emission intensity. This study aims to comprehend the effects of Ca2+ incorporation into NTSO, especially to the structural and optical emission properties. Na2(1-x)CaxTiSiO5 samples (x = 0.00; 0.01; 0.05; 0.10; 0.15; 0.20; 0.25; 0.50; 1.00) were synthesized by solid-state reaction method. Structural properties were characterized using X-ray and neutron diffraction, as well as LeBail and Rietveld refinement analyses. The photoluminescence properties were studied by room temperature photoluminescence spectroscopy to observe emission intensity variation with the Ca2+ ion concentration increments. The X-ray and neutron diffraction in the range of 0.00 ? x ? 0.25 shows that Na2(1-x)CaxTiSiO5 samples have identical structure with NTSO, that is, orthorhombic with space group of Pmc21. Further increasing in Ca2+ ion concentration induces transformation from NTSO phase with orthorhombic structure to monoclinic CaTiSiO5. X-ray diffractograms in the range of 0.05 ? x ? 0.25 exhibit a new peak at 2? = ~33o, whose intensity increases as Ca2+ concentration increases. There are three possibilites which might result in formation of the observed new peak, namely the existence of secondary phase, symmetry reduction of NTSO’s structure, or O2- displacement in Na2(1-x)CaxTiSiO5 lattice. Rietveld refinement analyses for the new peak conclude that the existence of Ca2+ gives rise to CaTiO3 phase in the range of 0.05 ? x ? 0.25, according to the best match between observed and calculated diffraction pattern. Lattice constant depression was perceived as Ca2+ ion concentration increases. These increments also change the coordination of TiO5 unit and change the Tim+ valence from +3 to +2. Light-induced excitation of Na2(1- x)CaxTiSiO5 at 4.84 eV produces blue light emission in range of 2.00-3.00 eV and UV light in range of 3.30-3.60 eV. The blue light emission properties were maintained for Na2(1-x)CaxTiSiO5 samples, regardless of Ca2+ concentration, whereas UV emission splits to two distinct peaks at 3.40 eV and 3.48 eV as Ca2+ concentration increases. The highest intensity for both UV and blue emission was observed when x = 0.15 and decreases with further increase of Ca2+ concentration. The calculated X-ray absorption spectrum and electronic structure of NTSO present that Tim+4p and 3d states in two different coordination environment play a major role in electronic transitions of that compound. Furthermore, there are overlapping 4p and 3d states in the energy range of 4.00-4.50 eV. This observation might cause orbital mixing of Tim+ 4p-3d states. Electronic excitation at 4.84 eV corresponds to charge transfer transition from O 2p to Ti 4p. Selection rule for electronic transition classifies this transition as forbidden, because ?l = 0. However, this charge transfer transition could be detected due to the orbital mixing of Tim+ 4p-3d states. The UV emissions of 3.40 eV and 3.48 eV were presumed to be originating from radiative relaxation of electrons residing in Ti 3d state from TiO5 and TiO6 units. Meanwhile, the blue emission of Na2(1-x)CaxTiSiO5 was suspected to be originating from d-d transition, according to Tanabe-Sugano diagram analysis. Tim+ valence variations provide a different number of electrons residing in 3d orbital, which might affect the emission intensity.