TBPO Research Articles

Effects of Green - Emitting Phosphor (La,Ce,Tb)PO_4:Ce:Tb on Luminous Flux and Color Quality of White LED Lamps

In this paper, we present and analyze the influence of (La,Ce,Tb)PO_4:Ce:Tb green phosphor (LaTb) toward the performance of the multi-chip white LED (MCW-LEDs) lamps including color uniformity, lumen output, Color Rendering Index (CRI), and Color Quality Scale (CQS). By mixing the LaTb green phosphor and the YAG:Ce yellow phosphor compounding under condition of 7000 K MCW-LEDs, this new approach can produce a huge meaningful change in lumen output and the angular color distribution of MCW-LEDs. We also study the interaction between the concentration and size of the LaTb particles with output flux, color uniformity, CRI, and CQS. The obtained results demonstrate that the higher lumen output, the higher color uniformity enhancement could be attained by adding the LaTb particles with a size range around 6-8 µm and the concentration around 1.5% in phosphor layer. Meanwhile, the decrease of the color rendering value (CRI) and the Color Quality Scale (CQS) tend to be stable and insignificant. In other words, the obtained results provide a prospective method which plays an important role in the development of MCW-LED manufacturing technology.

Synthesis of Hexagonal Prism (La, Ce, Tb)PO4 Phosphors by Precipitation Method

Hexagonal prism (La, Ce, Tb)PO4 green phosphors have been successfully prepared via a precipitation method route at ambient pressure from aqueous solution. The precipitation was obtained from lanthanide-nitrate complexes and (NH4)2HPO4 with citric acid as a structural modifier. The prism length diameter ratio and size can be tailored by varying the content of citric acid and the acidity of the solution, respectively. The mechanism of how the citric acid and acidity affect morphology has also been studied. Scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, and differential thermal analysis-thermogravimetry were used to characterize the morphology of the products and investigate the possible mechanism of formation and growth of the hexagonal prism. Furthermore, photoluminescence (PL) properties of (La, Ce, Tb)PO4 products were also carried out and compared with those of commercial phosphors.

(Gd,Yb,Tb)PO4 up-conversion nanocrystals for bimodal luminescence–MR imaging

Up-conversion (Gd,Yb,Tb)PO(4) materials and their potential for bimodal imaging have received little attention in the literature. Herein, we report the first study on the up-conversion emission of (Gd,Yb,Tb)PO(4) nanocrystals synthesized via a hydrothermal method at 150 °C. These materials exhibit ultraviolet, blue and green up-conversion emissions upon excitation with a 980 nm continuous wave laser diode. The intensity of the blue-emission band at 479 nm, ascribed to the cooperative up-conversion emission of a pair of excited Yb(3+) ions, depends on the Yb(3+)/Tb(3+) concentration ratio, calcination temperature and particle size. Strong green up-conversion emission of Tb(3+) is observed at 543 nm for the (5)D(4)→(7)F(5) transition. Relaxometry measurements reveal that the nanocrystals are efficient T(2)-weighted (negative) contrast agents which, combined with visible-light emission generated by infrared excitation, affords them considerable potential for being used in bimodal, photoluminescence-magnetic resonance, imaging.

Optical properties of (Y,Tb)PO 4 under VUV excitation

(Y,Tb)PO 4 were prepared by solid state reaction and their photoluminescence (PL) spectra were investigated under vacuum ultraviolet (VUV) excitation. The obtained results indicate that (Y,Tb)PO 4 can efficiently absorb the energy in the region of 112–243 nm and transfer it to the 5D 4 energy level of Tb 3+. After that, green light is emitted by Tb 3+ due to the transitions from 5D 4 energy level to the ground state. Under 147 nm excitation, the optimal emissive intensity is obtained when Tb 3+ concentration is about 20%, which is about 110% of commercial phosphor Zn 1.96SiO 4:0.04Mn 2+ with chromaticity coordinates of (0.354, 0.553) and the decay time of about 2.527 ms. According to the obtained experimental data, we tentatively explain the energy absorption, transfer and luminescent quenching for YPO 4:Tb 3+ under 147 nm excitation.