Development of a cyan blue-emitting Ba3La2(BO3)4:Ce3+,Tb3+ phosphor for use in dental glazing materials: color tunable emission and energy transfer

Green emission from trivalent cerium doped LaAlO3/MgO nano-composite for photonic and latent finger printing applications

A series of Ce³⁺ doped La_1-xCe_xAlO₃/MgO (x = 0, 0.7, 0.9, 1.0 and 2.0 mol%) nano-composites have successfully been synthesized employing the Pechini sol-gel method. XRD profiles assisted with Rietveld refinement results manifested the rhombohedral/face-centered structures of the two phases of the generated composite. Thermogravimetric results corroborate the crystallization temperature of the compound to be 900 °C, that further remains stable up to 1200 °C. Materials have been found to be wide band gap semi-conductors having E_g in the range of 5.5-5.8 eV. Photoluminescence studies reveal their green emission under UV excitation of 272 nm. Application of Dexter's theory and Burshtein model to PL and TRPL profiles, respectively reveals the q-q multipole interlinkages to be the viable cause of concentration quenching beyond optimum concentration of 0.9 mol%. Shifting of the energy transfer route from cross-relaxation to migration assisted mechanism with Ce³⁺ concentration has also been investigated. Other luminescence based parameters such as energy transfer probabilities, efficiencies, CIE and CCT have also been found to be in an admirable range. From the aforesaid results, it was observed that the optimized nano-composite (i.e. La_1-xCe_xAlO₃/MgO (x = 0.9 mol%)) can also be utilized for latent finger-printing (LFP) application that evinces its versatility for photonic as well as imaging applications.

The pH Value Control of Morphology and Luminescence Properties of Gd2O2S: Tb3+ Phosphors

Developing rare-earth doped oxysulfide phosphors with diverse morphologies has significant value in many research fields such as in displays, medical diagnosis, and information storage. All of the time, phosphors with spherical morphology have been developed in most of the related literatures. Herein, by simply adjusting the pH values of the reaction solution, Gd2O2S:Tb3+ phosphors with various morphologies (sphere-like, sheet-like, cuboid-like, flat square-like, rod-like) were synthesized. The XRD patterns showed that phosphors with all morphologies are pure hexagonal phase of Gd2O2S. The atomic resolution structural analysis by transmission electron microscopy revealed the crystal growth model of the phosphors with different morphology. With the morphological change, the band gap energy of Gd2O2S:Tb3+ crystal changed from 3.76 eV to 4.28 eV, followed by different luminescence performance. The samples with sphere-like and cuboid-like microstructures exhibit stronger cathodoluminescence intensity than commercial product by comparison. Moreover, luminescence of Gd2O2S:Tb3+ phosphors have different emission performance excited by UV light radiation and an electron beam, which when excited by UV light is biased towards yellow, and while excited by an electron beam is biased towards cyan. This finding provides a simple but effective method to achieve rare-earth doped oxysulfide phosphors with diversified and tunable luminescence properties through morphology control.

Bi3+ photoluminescence in Y1-xBixCa3(GaO)3(BO3)4 and energy transfer to Eu3+ and Tb3+ in co-doped phosphors

Bi³⁺ possesses outer shell lone pair electrons, and, thus the so-involved photoluminescence (PL) is sensitive to the surrounding coordination. Besides, the similarity in the structural chemistry between Bi³⁺ and rare earth (RE) ions inspires us to investigate the Bi³⁺-PL performance in RE³⁺-containing hosts. Herein, Y_1-xBi_xCa₃(GaO)₃(BO₃)₄ (0.01 ≤ x ≤ 0.15) compounds were prepared by a high temperature solid state reaction method. The successful cationic doping and phase purity were confirmed by powder X-ray diffraction analysis. This series of phosphors exhibit the very strong absorption of Bi^{3+ 1}S₀ → ³P₁ at 272 nm along with the intense blue emission with a maximum at 399 nm and a full width at half maximum (FWHM) of 59 nm. They retained 78.86% of the emission intensity at 150 °C, with reference to that at room temperature. Moreover, Bi³⁺ could also behave as a sensitizer to enhance the emission efficiency of RE³⁺ and thus to realize color-tunable phosphors. The energy transfer was proved in the co-doped phosphors Y_0.95-yBi_0.05Eu_yCa₃(GaO)₃(BO₃)₄ (0.05 ≤ y ≤ 0.6) and Y_0.95-zBi_0.05Tb_zCa₃(GaO)₃(BO₃)₄ (0.05 ≤ z ≤ 0.6), and color-tunable emissions from blue to red, or from blue to green were realized in these two series of phosphors.