Controlled Synthesis And Luminescent Properties Of Rare-Earth Doped Borate Phosphors

As a kind of ideal rare-earth doped host, borate materials have special optical properties, such as large electronic band gaps, strong photoluminescence intensity,and exceptional optical damage thresholds. In this paper, several rare-earth doped borate phosphors have been synthesized via solid-state reaction or hydrothermal method. And the energy transfer process among different rare earth, the influence of hydrothermal conditions on products’ morphology and photoluminescence intensity,possible formation mechanism, and quenching concentration were studied. The main content can be divided into the following aspects:1. Dy3+/Tb3+/Eu3+ doped KSr4(BO3)3 phosphors were successfully fabricated via high-temperature solid state reaction. The experimental results confirm that the energy transfer process of Dy3+â†'Tb3+ and Dy3+â†'Eu3+ existed in KSr4(BO3)3 host and were revealed to be dipole-dipole mechanism. The energy transfer efficiencies reach approximatively 60%/20% with increasing the Tb3+/Eu3+ doped concentration.Besides, the emitting colors of KSr4(BO3)3:0.005Dy3+, x Tb3+/y Eu3+ phosphors can be adjusted from the emitting colors of Dy3+ to that of Tb3+/Eu3+ via tuning the Tb3+/Eu3+doped concentration. In especial, the CIE chromaticity coordinates(0.334, 0.351) of KSr4(BO3)3:0.005Dy3+, 0.015Eu3+ phosphors is extremely close to standard white light(0.33, 0.33).2. Different morphologies Ln BO3(Ln=Y, Gd, and Lu) were synthesized via a facile hydrothermal reaction between Ln(OH)CO3(Ln=Y, Gd, Lu) colloid spheres which were prepared by a urea-based homogeneous precipitation process and different boron sources(Na2B4O7·10H2O, Na BO2·4H2O, or H3BO3), respectively. The mount of boron source and composition of the solvent play an important role in controlling the products’ morphology. The formation mechanism of different morphologies Ln BO3(Ln=Y, Gd, and Lu) went through different process: dissolution and recrystallization,Ostwald ripening, and two-stage growth process/lattice tension or surface interactionof the edge areas of the primary particles. The intrinsic geometry and crystallinity of different morphologies product have great influence on their photoluminescence intensity. And the quenching concentration of Eu3+/Tb3+ in Ln BO3(Ln=Y, Gd, and Lu)hosts were relatively high.3. Different morphologies Gd BO3 were synthesized via a hydrothermal reaction between Gd(OH)3 nanorods and different boron sources(H3BO3, Na2B4O7·10H2O, or Na BO2·4H2O), respectively. Pancake-like, flower-like, and leaf-like Gd BO3 went through different process: oriented attachment, dissolution and recrystallization, and oriented growth. Different crystallinity and specific surface area of different morphologies Gd BO3 result in their different photoluminescence intensity: flower-like one > leaf-like one > pancake-like one. The quenching concentration of flower-like Gd BO3:Eu3+ is 0.25. The quantum efficiency of the Gd BO3:0.25Eu3+ phosphor is14.30% which is higher than that of the commercial red-emitting Y2O3:Eu3+(12.2%).