Luminescence Thermometry Based on the Upconversion Luminescence from the Stark Sublevels of BaY2F8:Yb3+, Tm3+ Phosphor.

Visible and near-infrared (NIR) upconversion luminescence (UCL) emissions originating from the BaY2F8: Yb3+, Tm3+ systems were investigated under a laser excitation at 980 nm. The BaY2F8:20 mol% Yb3+, x mol% Tm3+ and BaY2F8: y mol% Yb3+, 0.5 mol% Tm3+ phosphors showed prominent UCL at 800 and 810 nm. The optimized doping concentrations of Yb3+ and Tm3+ in the BaY2F8 host matrix were evaluated, their spectroscopic properties were determined, and studies on their temperature-dependent behaviour were carried out. The temperature-sensing properties were studied by generating the fluorescence intensity ratio (FIR) of the UCL peaks originating from the thermally-coupled energy levels of the Tm3+ ions. The Stark sublevels of 1G4 level of Tm3+ ions were utilized to estimate the temperature-sensing abilities of the phosphor.

Dopant distribution and influence of sonication temperature on the pure red light emission of mixed oxide phosphor for solid state lighting.

In this study, europium doped yttrium gadolinium (Y1.4Gd0.5Eu0.1O3) mixed oxide phosphors were synthesized by a sonochemical method at different growth temperatures (50°C, 100°C, 150°C and 200°C) for pure red light emission applications. The compositional identification, presence of dopants and the distribution of doping materials in the crystal lattice was studied by TOF-SIMS. The formation and growth mechanisms in the sonochemical synthesis of Y1.4Gd0.5Eu0.1O3 nanophosphors are discussed in detail. Different spectral and Judd-Ofelt parameters were estimated from photoluminescence data. Optical gain and efficiency parameters were calculated with the variation of synthesis environment and an efficient synthesis method to make good red emitting phosphors for solid-state lighting and display applications were proposed.

The energy transfer phenomena and colour tunability in Y2O2S:Eu(3+)/Dy(3+) micro-fibers for white emission in solid state lighting 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.

Synthesis, thermal and spectroscopic characterization of Caq2 (calcium 8-hydroxyquinoline) organic phosphor.

Bluish-green photoluminescence from calcium 8-hydroxyquinolate (Caq(2)) powder, synthesized by a co-precipitation route, and a blended Caq(2):PMMA thin film is reported. The film was obtained by mixing the Caq(2) powder with PMMA (Polymethylmethacrylate) in a chloroform solution. X-ray diffraction analyses confirm the formation of the Caq(2) powder and thin film. Further structural elucidation was carried out using Fourier transform infrared spectroscopy (FTIR) in which the stretching frequencies of the Caq(2) bonds were determined. Bluish-green photoluminescence with a maximum at 480 nm was observed from the powder and the emission was red-shift by 10 nm in the case of the thin film. The UV-vis absorption bands were split and shifted due to different orientations of the Caq(2) molecules in both the powder and thin film. It was confirmed by thermogravimetric (TGA) and differential thermal analysis (DTA) that the Caq(2) powder was stable up to ≈ 380 °C. Atomic force microscopy images showed the continuous distribution of the Caq(2) atoms in the PMMA thin film. X-ray photoelectron spectroscopy data was used to estimate the binding energies of the chemical bonding in the Caq(2) powder complex. The optical properties of the Caq(2) powder and thin film were evaluated for possible applicable in organic light emitting devices.