J.J. Terblans

Defect correlated fluorescent quenching and electron phonon coupling in the spectral transition of Eu3+ in CaTiO3 for red emission in display application

This paper reports on the defect correlated self-quenching and spectroscopic investigation of calcium titanate (CaTiO3) phosphors. A series of CaTiO3 phosphors doped with trivalent europium (Eu3+) and codoped with potassium (K+) ions were prepared by the solid state reaction method. The X-ray diffraction results revealed that the obtained powder phosphors consisted out of a single-phase orthorhombic structure and it also indicated that the incorporation of the dopants/co-dopants did not affect the crystal structure. The scanning electron microscopy images revealed the irregular morphology of the prepared phosphors consisting out of μm sized diameter particles. The Eu3+ doped phosphors illuminated with ultraviolet light showed the characteristic red luminescence corresponding to the 5D0→7FJ transitions of Eu3+. As a charge compensator, K+ ions were incorporated into the CaTiO3:Eu3+ phosphors, which enhanced the photoluminescence (PL) intensities depending on the doping concentration of K+. The concentratio...

Identification of Eu oxidation states in a doped Sr 5 (PO 4 ) 3 F phosphor by TOF-SIMS imaging

An Eu-doped Sr5(PO4)3F phosphor with a hexagonal apatite structure was prepared by a urea assisted combustion method. There was evidence of the reduction of Eu3+ to Eu2+ based upon the photoluminescence data. This was confirmed with X-ray photoelectron spectroscopy. Normally, it is very difficult to distinguish between two oxidation states with time-of-flight secondary ion mass spectrometry (TOF-SIMS), but it is shown that the parallel detection capability of the technique allows full molecular and isotopic characterization of the matrix chemistry. The two states were detected by the EuF+ and EuF2+ species, ostensibly the Eu(II) and Eu(III) oxidation states, respectively.

Surface chemical reactions during electron beam irradiation of nanocrystalline CaS:Ce3+ phosphor

The effects of accelerating voltage (0.5–5 keV) on the green cathodoluminescence (CL) of CaS:Ce3+ nanocrystalline powder phosphors is reported. An increase in the CL intensity was observed from the powders when the accelerating voltage was varied from 0.5 to 5 keV, which is a relevant property for a phosphor to be used in field emission displays (FEDs). The CL degradation induced by prolonged electron beam irradiation was analyzed using CL spectroscopy, x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The AES data showed the decrease in the S peak intensity and an increase in the O peak intensity during electron bombardment. The CL intensity was found to decrease to 30% of its original intensity after about 50 C/cm2. XPS was used to study the chemical composition of the CaS:Ce3+ nanophosphor before and after degradation. The XPS data confirms that a nonluminescent CaSO4 layer has formed on the surface during the degradation process, which may partially be responsible for the C...

Kinetics near the discontinuous surface transition in the Cu(Ag)(111) binary segregating system

Abstract The kinetics of the segregating element silver in the system Cu(111)(Ag) was measured at temperatures close to where the discontinuous transition in the silver surface concentration versus temperature occurs. The seemingly complex kinetic behaviour of two-step diffusion and anomalous segregation processes could be fitted using only the surface segregation energy Δ G , the surface interaction parameter Ω S and the bulk diffusion coefficient D parameters.

Dopant distribution and influence of sonication temperature on the pure red light emission of mixed oxide phosphor for solid state lighting

In this study, europium doped yttrium gadolinium (Y1.4Gd0.5Eu0.1O3) mixed oxide phosphors were synthesized by a sonochemical method at different growth temperatures (50°C, 100°C, 150°C and 200°C) for pure red light emission applications. The compositional identification, presence of dopants and the distribution of doping materials in the crystal lattice was studied by TOF-SIMS. The formation and growth mechanisms in the sonochemical synthesis of Y1.4Gd0.5Eu0.1O3 nanophosphors are discussed in detail. Different spectral and Judd-Ofelt parameters were estimated from photoluminescence data. Optical gain and efficiency parameters were calculated with the variation of synthesis environment and an efficient synthesis method to make good red emitting phosphors for solid-state lighting and display applications were proposed.

Cathodoluminescence degradation of Y2SiO5:Ce thin films

Cathodoluminescence (CL) intensity of cerium-doped yttrium silicate (Y2SiO5:Ce) phosphor thin films grown by pulsed laser deposition were investigated for possible application in low voltage field emission displays (FEDs). A thin layer of tin oxide (SnO2) was ablated on some of the films in order to investigate the effect of the coated layer on the degradation of the CL intensity. Auger electron spectroscopy (AES) and CL spectroscopy were used to monitor changes in the surface chemical composition and luminous efficiency of the thin films. AES and CL spectroscopy were done with 2keV energy electrons and with beam current densities of 26 and 52mAcm−2. Measurements were done in high vacuum and in oxygen pressures of 1×10−8, 1×10−7, and 1×10−6Torr. Residual gas mass analysis showed that the adventitious carbon (C) was removed from the surface as volatile gas species, which is consistent with the electron stimulated surface chemical reaction model. The SnO2 coated thin films resulted in a lower but more stabl...

Orientation dependence of the surface segregation kinetics in single crystals

Experimental results are presented that support an earlier hypothesis that the bulk diffusion near surfaces is orientation dependent. From a literature study, the calculated surface energy of the (110) surface is higher than that of the (111) surface in fcc crystals, which could lead to different values of the bulk vacancy formation energy. This energy term determines the equilibrium bulk vacancy concentration and consequently also the bulk diffusion coefficient. Experimental surface segregation results were obtained for Cu(0.1%Sb) crystals for the said (110) and (111) surfaces using the linear heating method. The results, D 110 > D confirm the assumptions, and the order of magnitude experimental values of the activation energies are compatible with the calculated surface energies from the literature.

Review on electron stimulated surface chemical reaction mechanism for phosphor degradation

Standard cathodoluminescent phosphors normally lose brightness upon bombardment with electron beams. A combination of techniques such as x-ray photoelectron spectroscopy, Auger electron spectroscopy, and cathodoluminescence (CL) spectroscopy was used to show that the main reason for the degradation in CL intensity is the formation of a nonluminescent “dead layer” on the surface due to an electron stimulated surface chemical reaction. The decrease in luminance was found to be a result of the growth of the dead layer. Different phosphors which include sulfide-based as well as oxide-based phosphors reacted similarly under electron bombardment. When ZnS phosphor powder was exposed to the electron beam in a water-rich O2 ambient, a chemically limited ZnO layer was formed on the surface. A layer of ZnSO4 was formed on the surface during the electron beam degradation of the ZnS phosphor powder in a dry O2 ambient. The electron stimulated reaction led to the formation of a luminescent SiO2 layer on the surface of...

SYNTHESIS AND DEGRADATION OF THE PbS NANOPARTICLE PHOSPHORS EMBEDDED IN SiO2 (SiO2:PbS)

PbS nanoparticle phosphors embedded in SiO2 were synthesized at room temperature by the sol–gel method. The as-prepared SiO2:0.134 mol% PbS nanoparticles were ground and annealed in atmosphere. Changes in the cathodoluminescence (CL) brightness and the surface chemical composition of the SiO2:0.134 mol% PbS nanoparticle powders were investigated using a Fiber Optics PC2000 spectrometer for CL and Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) for the surface chemical analysis. The chemical composition of the powders was analyzed by an energy-dispersive spectrometer (EDS). The CL intensity decreased when the powders were irradiated with a beam of electrons at 2 keV energy and a beam current density of 54 mA/cm2 in an ultra-high vacuum chamber at oxygen (O2) pressures ranging between 5 × 10-8 and 2 × 10-7 Torr for several hours. The O2 Auger peak-to-peak height (APPH) decreased as the CL intensity decreased. XPS analysis on the degraded spot showed the development of characteristic SiO, SiOx, and elemental Si peaks on the low-energy side of the SiO2 peak. The desorption of O2 from the surface, which resulted in a decrease in the CL intensity is attributed to the dissociation of SiO2 into elemental Si and O2 by the electron bombardment. The degradation was less severe at higher oxygen pressures. PbSO4 was also formed on the surface during the electron beam degradation process.

Equilibrium surface segregation of silver to the low-index surfaces of a copper single crystal

The equilibrium surface segregation of Ag to the low-index surfaces of Cu single crystals is presented. It is found that the close-packed surface of the (111) orientation allows a high interaction parameter resulting in a discontinuous transition in the surface concentration against temperature, as well as a step in the segregation kinetics. In contrast, the rougher surfaces of the (110) and (100) orientations yield smaller interaction parameter values and a smooth transition in surface coverage against temperature is observed.