희토류 이온이 첨가된 NaBaBO3 형광체의 형광 특성 및 에너지 전달 연구

Abstract

Rare-earth-doped NaBaBO3 phosphors were synthesized by using the solid state reaction method. The reagents Na2CO3, BaCO3, and H3BO3 of high purity grade were used as starting compounds. The Tb3+, Eu3+, Dy3+, Ce3+ ions are doped in the NaBaBO3 lattices with concentration of 0.1, 0.5, 1.0, 5.0, 10, 15 and 20 mol%. The formation of the NaBaBO3 crystals for different rare-earth ion concentrations was confirmed by x-ray powder diffraction (XRD) patterns and it was observed no obvious impurity phases. Emission and excitation spectra of the rare-earth-doped NaBaBO3 were measured at room temperature and it is found that the spectra depend strongly on concentration rare-earth ions in NaBaBO3. The assignments of energy levels due to the 4f - 4f transitions of Tb3+, Eu3+ and Dy3+ in NaBaBO3 from the excitation and emission spectra are made by considering the crystal field symmetry and selection rules. The intense Ce3+ emission is observed in the wavelength region 350-550 nm peaking at 460 nm. The optimum concentration for the luminescence intensity is found to be 1 mol%. The Eu3+ emission at 615 nm in NaBaBO3 are observed at the Eu3+-concentration of 15 mol% in maximum intensity. Under excitation into the Ce3+ absorption band at 325 nm Eu3+-emission is observed together with the Ce3+ emission band due to the energy transfer from Ce3+ to Eu3+. The white light emission is realized by co-doping of Ce3+ and Eu3+ in in NaBaBO3. The white-light emission is tunable from cold to warm white by controlling the Eu3+ concentration. In the emission spectra of Dy3+ two intense bands at around 484 nm (blue) and 577 nm (yellow) regions corresponding to 4F9/2 → 6HJ (J = 15/2, 13/2) transitions, respectively, are observed. Energy transfer process, cross relaxation, concentration quenching and luminescence decays are discussed in the NaBaBO3 lattices.