De-Yin Wang

BaZrSi3O9:Eu2+: a cyan-emitting phosphor with high quantum efficiency for white light-emitting diodes

In this paper, a cyan-emitting phosphor BaZrSi3O9:Eu2+ was synthesized and evaluated as a candidate for white light emitting diodes (WLEDs). This phosphor shows strong and broad absorption in 380–420 nm region, and the emission intensity of the optimized BaZrSi3O9:Eu2+ was found to be 90% and 198% of that of the commercial BaMgAl10O17:Eu2+ (BAM:Eu2+) under excitation at 405 nm and 420 nm, respectively. Upon excitation at 405 nm, the quantum efficiency of the optimized BaZrSi3O9:Eu2+ is 83% of that of BAM:Eu2+. The performance of this phosphor was further tested to fabricate white LED lamps. By coating BaZrSi3O9:Eu2+ with a green-emitting (Ba,Sr)2SiO4:Eu2+ and a red-emitting CaAlSiN3:Eu2+ on a near-ultraviolet (405 nm) LED chip, driven by a 350 mA forward bias current, intense warm white light with a color rendering index of 90 has been produced.

Crystal structure of blue–white–yellow color-tunable Ca4Si2O7F2:Eu2+,Mn2+ phosphor and investigation of color tunability through energy transfer for single-phase white-light near-ultraviolet LEDs

The crystal structure of Ca4Si2O7F2:Eu2+,Mn2+ was refined and determined from X-ray diffraction (XRD) profiles obtained using a synchrotron light source by the Rietveld refinement method. It was found to crystallize into a monoclinic structure with the P21/c(14) space group. On examining the Mn2+-concentration-dependent photoluminescence properties, we found that the emission colors could be tuned from blue (0.152, 0.112) to white-light (0.351, 0.332) and eventually to yellow (0.430, 0.423) through energy transfer by changing the Eu2+/Mn2+ ratio. Moreover, energy transfer from a sensitizer Eu2+ to an activator Mn2+ occurs via a resonance-type dipole–quadrupole interaction mechanism, and the critical distances of the energy transfer were calculated to be 11.66 A and 12.61 A using concentration quenching and spectral overlap methods, respectively. Combining a 400 nm near-ultraviolet (NUV) chip and a single-phase white-emitting (Ca0.96Eu0.01Mn0.03)4Si2O7F2 phosphor produced a white-light NUV LED with CIE chromaticity coordinates of (0.347, 0.338) and a warm color temperature of 4880 K.

A Novel Tunable Green- to Yellow-Emitting β-YFS:Ce3+ Phosphor for Solid-State Lighting

A Ce(3+)-activated fluorosulfide phosphor (β-YFS:Ce(3+)) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce(3+) ions occupied. The emission band with a maximum at 495 nm of β-Y(0.99)Ce(0.01)FS phosphor was characterized by the 4f-5d transitions of Ce(3+) ion. With increasing Ce(3+) concentration, the emission variations were observed from 495 to 547 nm. When β-YFS:Ce(3+) phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting β-YFS:Ce(3+) can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.

Controlled synthesis and luminescent properties of monodispersed PEI-modified YVO4:Bi3+,Eu3+ nanocrystals by a facile hydrothermal process

A series of water-soluble YVO4:Bi3+,Eu3+ nanocrystals, with surfaces functionalized by a branch polyethylenimine (BPEI) polymer, have been synthesized via a one-pot hydrothermal method. It was found that the particle size and crystal morphology could be efficiently controlled by different reaction temperatures, pH values and molecular weights of the BPEI polymer. The surface modification of the nanocrystals was characterized using Fourier transform infrared spectroscopy (FT-IR). The highly crystalline YVO4:Bi3+,Eu3+ nanoparticles, with an average diameter of 20 nm, can be dispersed in water due to the presence of amino ligands. When conjugated with biomolecules, the YVO4:Bi3+,Eu3+ nanocrystals retain their strong red emission, peaking at 619 nm under near-ultraviolet (n-UV) excitation. The results indicate that YVO4:Bi3+,Eu3+ nanocrystals can serve as a promising candidate for biological imaging, and immunoassay applications.

Host Sensitization of Tb3+ Ions in Tribarium Lanthanide Borates Ba3Ln (BO3)3 (Ln = Lu and Gd)

The vacuum-ultraviolet (VUV) spectroscopic properties of undoped and Tb(3+)-doped borates Ba(3)Ln(BO(3))(3) (Ln = Lu and Gd) with different crystal structures were investigated by using synchrotron radiation. Ba(3)Lu(BO(3))(3) (BLB) crystallizes in a hexagonal structure, whereas Ba(3)Gd(BO(3))(3) (BGB) crystallizes in a trigonal structure. The maximum host absorption for BLB and BGB was found to locate at ~179 and ~195 nm, respectively. Upon host excitation, BLB exhibits an intrinsic broad UV emission centered at 339 nm, which is attributed to the recombination of self-trapped excitons that may presumably be associated with band-gap excitations or molecular transitions within the BO(3)(3-) group. In contrast to BLB, no broad emission but line emission ascribed to a Gd(3+)(6)P(J)-(8)S(7/2) transition was observed in the emission spectrum of BGB. Upon doping of Tb(3+) ions into the hosts of BLB and BGB, an efficient energy transfer from the host excitations to Tb(3+) via host/Gd(3+) emission was observed, showing that host sensitization of Tb(3+) occurs in these rare-earth borates.

α-(Y,Gd)FS:Ce3+: a novel red-emitting fluorosulfide phosphor for solid-state lighting

A novel Ce3+-doped fluorosulfide phosphor, α-(Y,Gd)FS:Ce3+, was first investigated as a new candidate for application in phosphor-converted light emitting diodes (LEDs) and thin-film electroluminescence (TFEL) devices. The detailed crystal structure was investigated based on X-ray diffraction profiles using Rietveld refinement methods. This phosphor shows good absorption ranging from ultraviolet to visible region and broad saturated red emission, which can be tuned from 660 to 672 nm, and the photoluminescence (PL) intensity was demonstrated to be effectively enhanced by Gd3+ substitution.

Photoluminescence investigations on a novel green-emitting phosphor Ba3Sc(BO3)3:Tb3+ using synchrotron vacuum ultraviolet radiation

Vacuum ultraviolet (VUV) spectroscopic properties of undoped and Tb3+-doped Ba3Sc(BO3)3 were investigated by using synchrotron radiation. The Tb3+-doped Ba3Sc(BO3)3 sample crystallized in a flower-like shape even was synthesized at 1100 °C. Upon VUV excitation, Ba3Sc(BO3)3 exhibited an intrinsic broad UV emission centered at 336 nm, which results from radiative annihilation of self-trapped exciton (STE) that may presumably be associated with band-gap excitations or molecular transitions within the BO33− group. The maximum host absorption for Ba3Sc(BO3)3 was found at about 180 nm. Upon doping of Tb3+ ions into Ba3Sc(BO3)3, an efficient energy transfer from the host excitations to Tb3+via STE emission was observed, showing host sensitization of Tb3+ occurs. The energy transfer from host to Tb3+via STE emission in Ba3Sc(BO3)3:Tb3+ was studied as a function of temperature and Tb3+ doping concentration. It has been demonstrated that the energy transfer efficiency was increased with either increasing temperature or Tb3+ doping concentration. In the case of temperature dependent energy transfer, the energy transfer from the STE to Tb3+ is thermally activated, probably due to exciton mobility, while in the case of concentration dependent energy transfer, the energy transfer from the STE to Tb3+ is promoted due to a closer distance between the STE and Tb3+ at high Tb3+ concentration.

Charge Transfer Luminescence of Several Zirconium-Containing Compounds Using Synchrotron Radiation

Photoluminescence properties of pristine and Eu2+-doped zirconates, viz. BaZr(PO4)2, BaZr4(PO4)6, Ba2Zr2Si3O12, and Ca3ZrSi2O9, excited by vacuum ultraviolet (VUV) light using synchrotron radiation were studied. The undoped zirconates show self-activated emission in the 300–340 nm region under VUV excitation, which is ascribed to the Zr4+-O2− charge transfer luminescence. Upon doping Eu2+ into these compounds, no Eu2+ emission was observed in the rest of compounds, except for a weak Eu2+ emission observed in Ba2Zr2Si3O12:Eu2+. The quenching of Eu2+ luminescence is rationalized as the presence of Zr4+-Eu2+ metal-metal charge transfer.