Enhanced red light emission from LaBSiO5:Eu3+,R3+ (R=Bi or Sm) phosphors

Luminescent Inorganic Mixed borate phosphors materials for lighting

The need of new materials with desirable optical properties has become important in recent year. In particular, a need has emerged for compounds having better luminescent properties in various practical applications. Introduction of rare earth ions as activators improves the luminescence properties of the compounds considerably. Boron is one of the most abundant elements in the nature. It readily combines with almost all other elements. In combination with oxygen; it forms borates comprising of various anions like BO₃ ^3- , B₂ O₅ ^4- , etc. Apart from these simple borates, several complex compositions exist involving mixed anions as well as double metal borates. Due to three-fold, or four-fold coordination of borate atoms Borates intrinsically possess characteristics that are advantageous for optical materials, which include wide transparency range, large electronic band gap, good thermal and chemical stability, low preparative temperature, optical stability with good nonlinear characteristics and exceptionally high optical damage threshold. The unique crystal structure of borates determines their enhanced UV transparency, good nonlinearity and relatively high resistance against laser induced damage. Some of these complex borates showing interesting luminescence properties are covered in this review. These include double borates containing rare earths RM₃ (BO₃ )₄ , Pentaborates LaMgB₅ O₁₀ , M₃ R₂ (BO₃ )₄ , where M is alkaline earth, mixed anion borates like aluminoborate SrAl₂ B₂ O₇ , Silicate-Borates like pekovite, SrB₂ Si₂ O₈ , Haloborates, M₂ B₅ O₉ X, where M is alkaline earth and X is halogen, phosphate borates, MBPO₅ , where M is alkaline earth. Phosphors base on these compositions find use in various applications like fluorescent lamps, colour TV, plasma display panels, high intensity discharge lamps based on Xenon, optically pumped solid state lasers, eye safe lasers, X-ray imaging.

The Preparation and Optical Properties of Novel LiLa(MoO4)2:Sm3+,Eu3+ Red Phosphor

Novel LiLa1-x-y(MoO4)2:xSm3+,yEu3+ (in short: LL1-x-yM:xSm3+,yEu3+) double molybdate red phosphors were synthesized by a solid-state reaction at as low temperature as 610 °C. The optimal doping concentration of Sm3+ in LiLa1-x(MoO4)2:xSm3+ (LL1-xM:xSm3+) phosphor is x = 0.05 and higher concentrations lead to emission quenching by the electric dipole-electric dipole mechanism. In the samples co-doped with Eu3+ ions, the absorption spectrum in the near ultraviolet and blue regions became broader and stronger than these of the Sm3+ single-doped samples. The efficient energy transfer from Sm3+ to Eu3+ was found and the energy transfer efficiency was calculated. Under the excitation at 403 nm, the chromaticity coordinates of LL0.95-yM:0.05Sm3+,yEu3+ approach to the NTSC standard values (0.670, 0.330) continuously with increasing Eu3+ doping concentration. The phosphor exhibits high luminous efficiency under near UV or blue light excitation and remarkable thermal stability. At 150 °C, the integrated emission intensity of the Eu3+ remained 85% of the initial intensity at room temperature and the activation energy is calculated to be 0.254 eV. The addition of the LL0.83M:0.05Sm3+,0.12Eu3+ red phosphors can improve the color purity and reduce the correlated color temperature of WLED lamps. Hence, LL1-x-yM:xSm3+,yEu3+ is a promising WLED red phosphor.

Luminescent properties and energy transfer in the green phosphors LaBSiO5:Tb3+, Ce3+

LaBSiO5 phosphors doped with Ce(3+) and Tb(3+) were synthesized using the conventional solid-state method at 1100 °C. The phase purity and luminescent properties of these phosphors are investigated. LaBSiO5:Tb(3+) phosphors show intense green emission, and LaBSiO5 phosphors doped with Ce(3+) show blue-violet emission under UV light excitation. LaBSiO5 phosphors co-doped with Ce(3+) and Tb(3+) exhibit blue-violet and green emission under excitation by UV light. The blue-violet emission is due to the 5d-4f transition of Ce(3+) and the green emission is ascribed to the (5) D4 → (7) F5 transition of Tb(3+). The spectral overlap between the excitation band of Tb(3+) and the emission band of Ce(3+) supports the occurrence of energy transfer from Ce(3+) to Tb(3+), and the energy transfer process was investigated.