THE SYNTHESIS OF PHOTOLUMINESCENCE MATERIAL OF CAAL2O4: MN4+ BY MEANS OF HYDROTHERMAL METHOD AND ITS CHARACTERIZATION

• Main Author: WAHYUNI ( NIM : 20513303 ), RIZKY
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/24083
• Institution: Institut Teknologi Bandung

<p align="justify">Utilization of White Light Emitting Diodes (WLED) is becoming the primary choice in the lighting system. WLED has many advantages compared to conventional illumination such as high efficiency, long lifetime, and environmental friendly. WLED is usually obtained from a combination of a blue InGaN phosphor chip coated with yellow phosphor (Y, Gd)3(Al, Ga)5O12: Ce3+. The WLED generally has low Color Rendering Index (CRI) due to the lack of red emission contributions. Ion Mn4+ is a promising dopant to produce red luminescence. Dopant Mn4+ show broad absorption at wavelenght of 300 nm - 480 nm and emits light in the range of 600 nm - 700 nm. CaAl2O4 become active luminescence materials because it has a variety of cation site which will provide various Mn4+ distribution. This research were conducted by doing the synthesis of photoluminescence material of CaAl2O4 with dopant Mn4+. The synthesis method is hydrothermal assisted sintering. The host material of CaAl2O4 was first synthesized to obtain the optimum condition. At precursors were weighed stoichiometrically and dissolved together with urea which acts as a mineralizer in deionized water. Then the homogeneous mixture was hydrothermalized at 220 °C for 24 hours. The results of XRD characterization showed that host material did not form on the hydrothermal conditions. The results of hydrothermal then was sintered repeatedly at 1300 °C for 6 hours and 8 hours. The pattern of powder X- ray diffraction showed characteristic peaks of the host CaAl2O4, secondary phase of CaAl4O7 and Ca12Al14O33. Host volume fraction which is obtained from the results of refinement using the Fullprof program with Rietveld method is 91.86%. This is the optimum condition of host CaAl2O4 formation and subsequently used to synthesized of CaAl2O4: Mn4+ (1%). Based on the XRD data, dopant related material’s peaks were not found. It is proved that the dopant has been successfully inserted into the host. The volume fraction of CaAl2O4: Mn4+ (1%) increases to 95.20% based on refinement results. Photoluminescence properties of CaAl2O4: Mn4+ (1%) were measured at room temperature. There were no differences in emissions spectrum between host and CaAl2O4: Mn4+ (1%). The concentration of Mn dopant was increased to 3% and 6% subsequently and the photoluminescence properties were measured again. Unfortunately, also there were no differences in emissions spectra between host and CaAl2O4: Mn4+ again although the dopant concentration has been enhanced. This show that at the optimum condition do not generate emissions of dopant Mn4+. The long high temperature sintering time can eliminate the active center of ion Mn4+ luminescence because the valence state of Mn4+ is unstable under radiation or thermal conditions. Sintering time at 1300 °C is shortened to 1 hour, 2 hours, 4 hours, and 6 hours. The photoluminescence properties of host and CaAl2O4: Mn4+ (3%) the were measured again. There are differences of the emission spectra between host and CaAl2O4: Mn4+ (3%). CaAl2O4: Mn4+ (3%) emissions measured with &#955;ex 325 nm, 365 nm, and 488 nm were still emitting at a wavelength of 654 nm. The emission at a wavelength of 654 nm is a transition from forbidden spin (2E (rumus) 4A2g) in Mn4+ assisted by phonons. The emission intensity of dopant Mn4+ decreases as the sintering time increases. Excitation of CaAl2O4: Mn4+ (3%) is clearly observed at wavelength of 340 nm and 470 nm which are allowed transitions of 4A2g (rumus) 4T1g (F) and 4A2g(rumus) 4T2g (F), respectively. The peak at 318 nm on the excitation spectrum is the charge transfer transitions from O2- (rumus)Mn4+. The XRD analysis proved that synthesized CaAl2O4: Mn4+ (3%) has nearly the same XRD pattern of CaAl2O4 host and the volume fraction is lower than the optimum condition.<p align="justify"> <br />