Huihong Lin

Luminescence of Ce3+ activated fluoro-apatites M5(PO4)3F (M = Ca, Sr, Ba) under VUV—UV and x-ray excitation

Fluoro-apatite M5(PO4)3 F( M= Ca, Sr, Ba) phosphors activated with Ce 3+ ions were prepared by a solid state reaction technique at high temperature. The excitation spectra in the VUV (vacuum ultraviolet)–UV range and the emission spectra in the UV–vis range together with decay time spectra are investigated and discussed. X-ray excited emission spectra were measured and light yields are calculated. The results revealed that Ca(II) sites are preferentially occupied at low doping concentration, and then Ca(I) sites are dominant with the increasing of concentration for Ce 3+ in Ca5(PO4)3F. In contrast, Ce 3+ ions mainly occupied the Sr(II)/Ba(II) sites in Sr5(PO4)3 Fa nd Ba5(PO4)3F even at higher doping concentration. The low light output seems to suggest that the materials are not suitable x-ray or gamma-ray phosphors. (Some figures in this article are in colour only in the electronic version)

Intense Emission of Ca5 ( PO4 ) 3F : Tb3 + under VUV Excitation and Its Potential Application in PDPs

In order to develop a suitable green phosphor for plasma display panels (PDPs), samples Ca 5-2x Tb x Na x (PO 4 ) 3 F for x = 0.20, 0.35, 0.50, 0.65, 0.80, and 0.95 were prepared by a solid-state reaction technique at high temperature. The vacuum ultraviolet (VUV, wavelength λ 50,000 cm -1 )-vis spectroscopic properties and decay characteristic were investigated. Because the phosphor Ca 5-2x Tb x Na x (PO 4 ) 3 F for x = 0.95 shows broad and strong absorption in the vacuum ultraviolet (VUV) range, exhibits higher intensive emission under 147/172 nm excitation, and has a shorter decay time (τ ∼ 2.19 ms) in comparison with the commercial green PDP phosphor Zn 2 SiO 4 /Mn 2+ , it is considered to be a promising green phosphor in PDPs.

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.

Enhanced luminescence of Ba 3 La(PO 4 ) 3 :Dy 3+ by codoping Gd 3+ ions and energy transfer between Gd 3+ and Dy 3+

The orthophosphate phosphors, Ba3La(PO4)3 activated with Dy3+ and Gd3+-Dy3+ ions, were prepared by a solid reaction technique at high temperature. Their spectroscopic properties were investigated in the vacuum ultraviolet (VUV)-visible range. We found that the introducing of Gd3+ greatly enhances the Dy3+ luminescence under 172 nm VUV excitation. The measurements on excitation spectra, emission spectra, and luminescence decay curves revealed that the energy transfer between Gd3+ and Dy3+ becomes more and more efficient with the increasing Gd3+ contents.

Luminescence of Ba2Ca(BO3)2 : Ce3+—influence of charge compensator, energy transfer and LED application

The luminescence properties of Ce3+ activated Ba2Ca(BO3)2 with K+ as a charge compensator have been investigated and compared with those with Na+-compensating. Energy transfer of Ce3+ in Ba2+ (i.e. Ce(1)3+) and Ca2+ (i.e. Ce(2)3+) sites has been proven by VUV?UV excitation and emission spectra, luminescence decays and time-resolved emission spectra. In addition, by combining Ba2Ca(BO3)2?:?Ce3+ phosphors with near-ultraviolet (n-UV) InGaN chips, the fabricated light-emitting diodes (LEDs) show intense bluish-green emission, and the phosphors exhibit good thermal stability.

Luminescence and site occupancies of Eu3+ in La2CaB10O19

Eu(3+)-activated La2CaB10O19 phosphors with nominal chemical formulae La(2-x)Eu(x)CaB10O19 and La2Ca(1-2x)Eu(x)Na(x)B10O19 were prepared. The luminescence properties under VUV-UV excitation were investigated. Luminescence spectra reveal Eu(3+) ions occupy both Ca(2+) and La(3+) sites in all samples. The O(2-)→ Eu(3+) charge transfer bands (CTBs) and the (5)D0→(7)F0 emissions of Eu(3+) at Ca (2+) site and La(3+) site are identified, respectively. The schematic energy levels for Eu(3+) in two sites were achieved. Luminescence decays of the (5)D0→(7)F0 transitions were measured for both sites.

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.

The VUV‐VIS Spectroscopic Properties of Dy3+ Ion in Phosphors M5‐2XDyXNaX(PO4)3F (M=Ca, Sr, Ba) and Their Potential Applications in Mercury‐Free Lamps

Abstract The phosphors, fluorapatites M5(PO4)3F (M=Ca, Sr, Ba) activated with Dy3+ ions, were prepared by a high‐temperature solid‐state reaction technique. The VUV‐UV excitation spectra and emission spectra under VUV/UV excitation were measured. The phosphors show broad and strong absorption near 172 nm and intensive emission with the chromaticity coordinates entering the white light region. Hence, the phosphors may be considered as suitable candidates for Hg‐free lamps.

A comparison of Ce3+ luminescence in X2Z(BO3)2 (X=Ba, Sr; Z=Ca, Mg) with relevant composition and structure

The VUV-UV spectroscopic properties of Ce3+ in Ba2Mg(BO3)(2), Ba2Ca(BO3)(2) and Sr2Mg(BO3)(2) were compared, and the relation between the energy of the 4f -> 5d transition of Ce3+ and the coordination environments of substituted alkaline earth ions was discussed. The chromaticity coordinates of Ce3+ activated X(2)Z(BO3)(2) (X=Ba, Sr; Z=Ca, Mg) phosphors were changeable from blue to whitish and further to green range by varying the doping concentration of Ce3+ or the types of substituted alkaline earth ions upon 172 nm excitation.

Studies of domain wall motion. I. Internal friction under magnetization

The internal friction (IF) measurement technique is used to study the magnetization of pure iron, nickel and Permalloy-42. The IF of samples undergoing a uniform magnetic field sweep is measured with a torsion pendulum. An IF peak is observed in the field range 0-10 Oe. The field sweeping increases the IF and hence the characteristic quantity is the difference between the IF measured in field sweeping and that in a static field, which is called dynamic internal friction. The dynamic IF shows a viscoelastic feature; it increases with increasing H/ omega where H is the field sweep rate and omega the angular frequency of the alternating strain. The behaviour of the dynamic IF shows that it is caused by the domain wall motion in field sweeping and thus is related to a magnetomechanical interaction.