Chenning Zhang

Photoluminescence properties of β-SiAlON:Yb2+, a novel green-emitting phosphor for white light-emitting diodes

Abstract We have synthesized Yb2+-activated Si6−zAlzOzN8−z (0.05ue251zue2512.3, 0.03 mol% ue251Yb2+ue2510.7 mol%) green phosphors by solid-state reaction at 1900 °C for 2 h under a nitrogen pressure of 1.0 MPa. Phase purity, photoluminescence and its thermal quenching were investigated. A single phase was obtained for all values of z and Yb2+ concentration. A distinct emission band was observed at 540 nm originating from the 5d–4f electronic transition in Yb2+ under 480 nm excitation. The photoluminescence properties mainly depended on the Yb2+ concentration and chemical composition of the matrix. The resultant phosphor showed high thermal stability, that is, the emission intensity at 150 °C was about 82% of that measured at room temperature. The experimental results indicate that β-SiAlON:Yb2+ is a potential green phosphor for white light-emitting diodes (LEDs), which use blue LEDs as the primary light source.

Optical Properties of Blue-Emitting Ce x Si6 − z Al z − x O z + 1.5x N8 − z − x for White Light-Emitting Diodes

In this work, blue-emitting CexSi6�zAlzxOz+1.5xN8�zx 0.3 z 2.5,0.5 x 2.5 phosphors were synthesized by firing pow- der mixtures of -Si3N4, AlN, Al2O3, and CeO2 at 1950°C fo r2hu nder 1.0 MPa N2. The resultant phosphors were characterized by phase identification, diffuse reflectance spectra, photoluminescence spectra, quantum efficiency, and temperature-dependent luminescence. The samples showed high purity at the overall range of the varied x and z values. A single broad emission band centered at about 486 nm at 410 nm excitation was observed. Moreover, the CexSi6�zAlzxOz+1.5xN8�zx phosphors showed high thermal stability, which could sustain 79-88% emission intensity measured at room temperature. These results indicate that the CexSi6�zAlzxOz+1.5xN8�zx phosphors are promising wavelength-conversion materials for white light emitting diodes LEDs using near-UV LED chips as the primary light source.

Strong Energy-Transfer-Induced Enhancement of Luminescence Efficiency of Eu2+- and Mn2+-Codoped Gamma-AlON for Near-UV-LED-Pumped Solid State Lighting

A series of Eu(2+)- and Mn(2+)-codoped γ-AlON (Al1.7O2.1N0.3) phosphors was synthesized at 1800 °C under 0.5 MPa N2 by using the gas-pressure sintering method (GPS). Eu(2+) and Mn(2+) ions were proved to enter into γ-AlON host lattice by means of XRD, CL, and EDS measurements. Under 365 nm excitation, two emission peaks located at 472 and 517 nm, resulting from 4f(6)5d(1) → 4f(7) and (4)T1(4G) → (6)A1 electron transitions of Eu(2+) and Mn(2+), respectively, can be observed. Energy transfer from Eu(2+) to Mn(2+) was evidenced by directly observing appreciable overlap between the excitation spectrum of Mn(2+) and the emission spectrum of Eu(2+) as well as by the decreased decay time of Eu(2+) with increasing Mn(2+) concentration. The critical energy-transfer distance between Eu(2+) and Mn(2+) and the energy-transfer efficiency were also calculated. The mechanism of energy transfer was identified as a resonant type via a dipole-dipole mechanism. The external quantum efficiency was increased 7 times (from 7% for γ-AlON:Mn(2+) to 49% for γ-AlON:Mn(2+),Eu(2+) under 365 nm excitation), and color-tunable emissions from blue-green to green-yellow were also realized with the Eu(2+) → Mn(2+) energy transfer in γ-AlON.

Role of Fluxes in Optimizing the Optical Properties of Sr0.95Si2O2N2:0.05Eu2+ Green-Emitting Phosphor

Chlorides of NH4Cl and SrCl2 and fluorides of AlF3 and SrF2 were added to raw materials acting as the flux for preparing the SrSi2O2N2:Eu2+ phosphor. The effects of the fluxes on the phase formation, particle morphology, particle size, and photoluminescence properties were investigated. The results revealed that particle size, particle morphology and photoluminescence intensity were largely dominated by the type of the flux material and its adding amount. The chloride-based flux was found to favor the formation of the SrSi2O2N2:Eu2+ phase. Among the chloride-based fluxes, the sample added with the SrCl2 flux presented the narrow particle distribution and cleaner surface, with enhanced emission intensity and an increased external quantum efficiency by 68% and 22%, respectively, compared with those of the sample without any flux adding.

Positional-dependent luminescence property of β-SiAlON:Eu2+ phosphor particle

The relationship between the luminescence property and particle faces of the β-SiAlON:Eu2+ phosphors was investigated by performing the cathodoluminescence (CL) measurements on the tip and side faces of the rod-like phosphor particles. It was found a positional dependence of the CL intensity on the particle faces, that is, the side face possessed higher CL intensity than the tip face, probably due to uneven distribution of the Eu2+ sites in the β-SiAlON host particles: the Eu2+ ions more intensively concentrated at the side face of the particle, particularly at the central area of the side face, than at the tip face.