Jiuping Zhong

Intensive emission of Dy 3+ in NaGd(PO 3 ) 4 for Hg-free lamps application

The phosphor NaGd(PO(3))(4):Dy(3+) was synthesized by solid-state reaction technique at high temperature. The vacuum ultraviolet (VUV)-UV excitation spectra and visible emission spectra under VUV/UV excitation were investigated. The sample NaGd(PO(3))(4):Dy(3+) showed suitable spectroscopic characteristics such as broad and strong absorption around 172 nm, intensive emission with the chromaticity coordinates (0.33, 0.38) in warm-white light region. Additionally, this efficient white-emitting phosphor is activated by a single Dy(3+) ion and with a lower preparation temperature, which tend to decrease the consumption of rare earth resource and energy. Therefore, the phosphor NGP:Dy(3+) may be considered as a suitable candidate for Hg-free lamps application.

Bright green-emitting, energy transfer and quantum cutting of Ba3Ln(PO4)3: Tb3+ (Ln = La, Gd) under VUV-UV excitation.

Tb3+ doped Ba3Gd(PO4)3 and Ba3La(PO4)3 phosphors were synthesized using the traditional high temperature solid state reaction method. The excitation, emission, and decay spectra were measured at room temperature. Efficient energy transfer (ET) from Gd3+ to Tb3+ exists in Tb3+ doped Ba3Gd(PO4)3, and the ET efficiency increases with the increase of Tb3+ concentration. The visible quantum cutting (QC) via cross relaxation was observed upon exciting low-spin (7D(J)) 5d levels of Tb3+ ions. Ba3Tb(PO4)3 sample shows relatively strong emission intensity in comparison with Zn2SiO4: Mn2+ (ZSM) upon 172 nm excitation, and with a decay time τ(1/10) about 6.4 ms under 351 nm excitation, indicating the potential application of this phosphor for plasma display panels (PDPs) and Hg-free lamps.

Structure Refinement and Two-Center Luminescence of Ca3La3(BO3)5:Ce3+ under VUV–UV Excitation

A series of Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) phosphors were prepared by a high-temperature solid-state reaction technique. Rietveld refinement was performed using the powder X-ray diffraction (XRD) data, which shows occupation of Ce(3+) on both Ca(2+) and La(3+) sites with a preferred location on the La(3+) site over the Ca(2+) site. The prepared samples contain minor second phase LaBO(3) with contents of ~0.64-3.27 wt % from the Rietveld analysis. LaBO(3):1%Ce(3+) was prepared as a single phase material and its excitation and emission bands were determined for identifying the influence of impurity LaBO(3):Ce(3+) luminescence on the spectra of the Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) samples. The luminescence properties of Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) samples under vacuum ultraviolet (VUV) and UV excitation were investigated, which exhibited two-center luminescence of Ce(3+), assigned to the Ce(1)(3+) center in the La(3+) site and Ce(2)(3+) center in the Ca(2+) site, taking into account the spectroscopic properties and the Rietveld refinement results. The influences of the doping concentration and the excitation wavelength on the luminescence of Ce(3+) in Ca(3)La(3(1-x))Ce(3x)(BO(3))(5) are discussed together with the decay characteristics.

Effects of crystal structure on the luminescence properties and energy transfer between Gd3+ and Ce3+ ions in MGd(PO3)4:Ce3+ (M = Li, Na, K, Cs)

Cerium-activated polyphosphates MGd(PO3)4 (M = Li, Na, K, Cs), were synthesized by a solid-state reaction technique at high temperature. The ultraviolet (UV) and vacuum ultraviolet (VUV) luminescence spectra of this series of samples were determined at room temperature (RT). On the basis of the VUV excitation spectra of MGd(PO3)4:1.0 at% Ce3+, the centroid shift ec, total crystal field splitting ecfs, and total redshift D(A) were calculated. According to the ligand polarization model, the values of the spectroscopic polarizability αsp were also calculated from the observed centroid shifts. It was found that the ec, ecfs, D(A) and αsp were influenced by the crystal structure. Based on the luminescence spectra of these polyphosphate samples, the energy level diagram of Gd3+–Ce3+ in MGd(PO3)4:Ce3+ systems was also proposed. Through the energy level diagram and the decay curves of Ce3+ emission, the energy transfer between Gd3+ and Ce3+ ions was investigated. It was found that there existed efficient energy transfer between Gd3+ and Ce3+ ions in MGd(PO3)4:Ce3+ systems. Considered the efficient energy transfer from Gd3+ to Ce3+ ions and short lifetime of Ce3+ emission, this series of compounds doped with Ce3+ ions could be used as promising scintillator materials.

Vacuum ultraviolet-ultraviolet and x-ray excited luminescence properties of Ba3Gd(BO3)3:Ce3+

The phosphors Ba3Gd(BO3)3:Ce3+ were prepared by a solid-state reaction technique at high temperature. The vacuum ultraviolet-ultraviolet and visible spectroscopic properties of the phosphors together with decay time curves are investigated and discussed. The spectroscopic properties are explained by occupancy of Ce3+ at two different Gd sites in the host lattice. The x-ray excited emission spectra of Ba3Gd(BO3)3:Ce3+ were studied and the number of photons emitted per unit of absorbed x-ray energy was calculated. The yield is rather poor and Ba3Gd(BO3)3:Ce3+ appears not a suitable x-ray phosphor.

Spectroscopic properties of vacancies and trap levels in Lu3Al5O12:Ce3+ crystals

Abstract In order to study the spectroscopic properties of vacancies and trap levels in Lu3Al5O12:Ce3+ (LuAG:Ce3+) crystal, the -oriented LuAG:Ce3+ crystal grown in pure nitrogen atmosphere by Czochralski method was annealed in oxidizing atmosphere (air) and reducing atmosphere (H2+N2), respectively. The excitation and emission spectra of LuAG:Ce3+ crystal after different thermal annealing treatments were measured in the temperature range of 8−450 K, and the thermally stimulated luminescence curves of LuAG:Ce3+ crystal were characterized. It is found that the oxygen vacancies in LuAG:Ce3+ crystal are effectively eliminated through the annealing treatment in air and four trap levels are observed in as-grown LuAG:Ce3+ crystal with temperature position peaking at 110, 210, 325 and 475 °C, respectively.

Luminescence properties and site occupancy of Ce3+ in Ba2SiO4: a combined experimental and ab initio study

Photoluminescence properties of Ba2−2xCexNaxSiO4 (x = 0.0005) prepared by a solid-state reaction method are first studied with excitation energies in the vacuum-ultraviolet (VUV) to ultraviolet (UV) range at low temperature. Five bands are observed in the excitation spectrum of Ce3+ 5d → 4f emission at 26.5 K. The highest energy band is attributed to the host excitonic absorption, from which the band gap energy of the host is estimated to be around 7.36 eV. The four lower energy bands are assigned to the 4f → 5d transitions of Ce3+ located at one of the two types of Ba sites in Ba2SiO4, based on a comparison of excitation spectra at different monitoring wavelengths. Under UV excitation, the material exhibits bright luminescence at 350–450 nm, with a fast decay time (∼26 ns at 4 K) and a high thermal quenching temperature (>500 K). In view of this, X-ray excited luminescence measurements are then conducted, and the results suggest a potential application of Ba2SiO4:Ce3+ as scintillation phosphors. Hybrid density functional theory (DFT) calculations within the supercell model are carried out to optimize the local structures of Ce3+ at the two Ba sites in Ba2SiO4, on which wave function-based ab initio embedded cluster calculations are performed to derive the 4f1 and 5d1 energy levels of Ce3+. On the basis of the calculated DFT total energies and the comparison between experimental and calculated 4f → 5d transition energies, we find that the luminescence originates predominantly from Ce3+ occupying nine-coordinated Ba2 sites. Furthermore, electronic properties of Ce3+ in Ba2SiO4 are evaluated to provide an understanding of the high thermal stability of the 5d luminescence at the level of electronic structures.

Luminescence properties of Na3LuSi3O9:Ce3+ as a potential scintillator material

Lutetium based oxyorthosilicate (Lu2SiO5:Ce3+/Lu2−xYxSiO5:Ce3+) and pyrosilicate (Lu2Si2O7:Ce3+) scintillators exhibit good scintillation performances in terms of light-yield and decay properties. Nevertheless, both of them have a high melting point (≥1900 °C) which is unfavorable to crystal growth. In this work, an alternative lutetium based silicate scintillator was proposed with a lower melting point (about 1500 °C): Na3LuSi3O9:Ce3+. The structure and thermal quenching properties of Na3LuSi3O9:Ce3+ were investigated. The emission spectra of Na3Lu0.99Ce0.01Si3O9 under UV and X-ray excitation as well as pulsed X-ray measurements were also determined. The phosphors show a broad emission band from 320 nm to 475 nm. Due to the suitable emission wavelength range, the fast decay properties and relative low melting point, Na3LuSi3O9:Ce3+ may be a potential novel inorganic scintillator material.