This paper reports on the defect correlated self-quenching and spectroscopic investigation of calcium titanate (CaTiO3) phosphors. A series of CaTiO3 phosphors doped with trivalent europium (Eu3+) and codoped with potassium (K+) ions were prepared by the solid state reaction method. The X-ray diffraction results revealed that the obtained powder phosphors consisted out of a single-phase orthorhombic structure and it also indicated that the incorporation of the dopants/co-dopants did not affect the crystal structure. The scanning electron microscopy images revealed the irregular morphology of the prepared phosphors consisting out of μm sized diameter particles. The Eu3+ doped phosphors illuminated with ultraviolet light showed the characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+. As a charge compensator, K+ ions were incorporated into the CaTiO3:Eu3+ phosphors, which enhanced the photoluminescence (PL) intensities depending on the doping concentration of K+. The concentration quenching of Eu3+ in this host is discussed in the light of ion-ion interaction, electron phonon coupling, and defect to ion energy transfer. The spectral characteristics and the Eu-O ligand behaviour were determined using the Judd-Ofelt theory from the PL spectra instead of the absorption spectra. The CIE (International Commission on Illumination) parameters were calculated using spectral energy distribution functions and McCamy's empirical formula. Photometric characterization indicated the suitability of K+ compensated the CaTiO3:Eu3+ phosphor for pure red emission in light-emitting diode applications.
This paper reports on the structural, optical and photometric characterization of an Eu(3+)/Dy(3+) doped yttrium oxysulfide phosphor (Y2O2S:Eu(3+)/Dy(3+)) for near white emission in solid state lighting. A series of Y2O2S phosphors doped with Eu(3+)/Dy(3+) were prepared by the hydrothermal method. The microstructures of the as-synthesized phosphors were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results reveal that the obtained powder phosphors have a single-phase hexagonal structure and also indicate that the incorporation of the dopants/co-dopants did not affect the crystal structure. The SEM images reveal the morphology of the prepared phosphors as an intense interpenetrating network of interconnected micro-fibers with a diameter of about 0.15 μm. The band gap of the phosphors was calculated from diffuse reflectance spectra using the Kubelka-Munk function. The Eu(3+), Dy(3+) doped and Eu(3+)/Dy(3+) co-doped phosphors illuminated with ultraviolet light showed characteristic red luminescence corresponding to the (5)D0→(7)FJ transitions of Eu(3+) and characteristic blue and yellow luminescence corresponding to the (4)F9/2→(6)H15/2 or (4)F9/2→(6)H13/2 transitions of Dy(3+). The luminescence spectra, the energy transfer efficiency and the decay curves of the phosphors indicated that there exists a strong energy transfer from Dy(3+) to Eu(3+) and this was demonstrated to be a resonant type via a dipole-quadrupole reaction. Furthermore, the critical distance of the Eu(3+) and Dy(3+) ions have also been calculated. By utilizing the principle of energy transfer it was also demonstrated that with an appropriate tuning of the activator content the Y2O2S:Eu(3+)/Dy(3+) phosphors can exhibit a great potential to act as single-emitting component phosphors for white light emission in solid state lighting technology.
Motivated from our previous studies on the upconversion properties of BaMgF:Yb,Tb phosphor, here we investigated the upconversion properties of BaMgF:Yb,Er phosphor. We demonstrate a two-way versatile approach for the fine-tuning of emission from green to the red region, by varying the dopant concentration and adjusting the pulse width of an infrared laser. The mechanism involved in tuning the emission color by laser power and pulse width variation was illustrated in detail. The temperature dependent upconversion spectra were studied by analyzing the fluorescence intensity ratio of the thermally coupled levels. The maximum sensitivity obtained is 83.29 × 10 K at 583 K, which is much higher than the temperature sensitivity reported for other fluoride based materials. Moreover, the influence of the excitation power density on the ability of the phosphor for temperature sensing was also investigated. We obtained a maximum (∼415 K) temperature detection at 2563 mW laser power. The obtained results illustrate the potential use of BaMgF:Yb,Er phosphor in an optical thermometer due to its highly sensitive temperature detection ability.
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