Yinrong Fu

Novel La3GaGe5O16 : Mn4+ based deep red phosphor: a potential color converter for warm white light

New non-rare-earth red phosphor La3GaGe5O16 : Mn4+ was prepared successfully via the traditional solid state reaction method. In this paper, we reported this red phosphor La3GaGe5O16 : Mn4+ as a promising red converter for warm white light under excitation at UV or blue light. The phase and microstructure of this red phosphor were characterized with aids of the XRD and SEM; the luminescent performance was investigated by the diffuse reflection spectra, photoluminescence (PL) spectra, and temperature-dependent PL/decay measurements. The excitation band of La3GaGe5O16 : Mn4+ phosphor covers a broad spectral region from 250 nm to 500 nm, which match well with the commercial near-UV and blue LEDs and can give intense bright red emission. The crystal field strength (Dq) and the Racah parameters (B and C) are calculated to evaluate the nephelauxetic effect of Mn4+ suffering from the La3GaGe5O16 host. The concentration quenching of Mn4+ in La3GaGe5O16 : Mn4+ occurs at a low content of 0.25% due to the dipole–dipole interaction in this work. We gained insight into the temperature-dependent relative emission intensity of La3GaGe5O16 : 0.25% Mn4+ phosphor, and we also reported the luminescence quenching temperature and the activation energy for thermal quenching (ΔE). In future, WLEDs will be made when this red phosphor was applied to the package of a UV/blue LED chip and YAG : Ce.

Reversible colorless-cyan photochromism in Eu2+-doped Sr3YNa(PO4)3F powders

Photochromic materials have attracted increasing interest as optical switches and erasable optical memory media. Here, we report on a novel reversible colorless-cyan photochromic powder material Sr3YNa(PO4)3F:Eu2+. The photochromic properties including coloring and bleaching are characterized by reflectance spectra after the powder is irradiated by different wavelengths of light for different irradiation times or processed by thermal treatment. The results show that it can be colored by short wavelength light (200–320 nm) and bleached by longer wavelength light (320–800 nm) or thermal treatment at 240 °C. The optimal doping concentration of Eu2+ is determined to be about 0.5 mol%. It shows high fatigue resistance in photochromism performance. Electrons in 4f ground levels excited by short wavelength irradiation to higher 5d states of Eu2+ and then captured by traps are responsible for the coloring process. Correspondingly, the release of trapped electrons from two kinds of traps with different depths causes the initially fast and later slow bleaching processes. The critical role of charge carrier motions between two different traps is discussed. The colorless-cyan photochromism can be explained semi-quantitatively on the basis of obtained results. A tentative model was proposed to illustrate the PC mechanism.

Preparation and characterization of a long persistent phosphor Na 2 Ca 3 Si 2 O 8 :Ce 3+

A novel host lattice Na2Ca3Si2O8 was used for synthesizing long persistent phosphors for the first time. A blue-emitting long persistent phosphor was prepared successfully via a traditional high temperature solid-state reaction method. The phase structure was checked by XRD. The photoluminescence and persistent luminescence decay properties of Ce3+-doped samples were studied systematically. The defects acting as traps were investigated by thermoluminescence. It demonstrated that the doping Ce3+ ions into the Na2Ca3Si2O8 host not only largely enriched the intrinsic traps but also introduced abundant new extrinsic traps which play a determining role in the generation of persistent luminescence. The origin of the persistent luminescence was analyzed and a related mechanism was systematically discussed based on a schematic diagram as well.

La 3 GaGe 5 O 16 :Cr 3+ phosphor: the near-infrared persistent luminescence

Long persistent phosphors in the near-infrared (NIR) region have attracted much attention due to the potential application in in vivo imaging. La3GaGe5O16:Cr3+ phosphor presents a NIR long persistent luminescence after the short UV-irradiation. La3GaGe5O16 host also exhibits a cyan persistent luminescence. The optimal concentration of Cr3+ in La3GaGe5O16 is experimentally about 0.01 and the afterglow time can last more than 30 min. The estimated trap depth which varies continuously as a function of delay time is evidence for the presence of a continuous trap distribution. In order to improve the performance of afterglow luminescence of the La3GaGe5O16:Cr3+, we modified composition around Cr3+ by adjusting the Ge/O content. La3GaGe5O16:Cr3+ is shown to be a new near-infrared persistent phosphor potentially suitable for in vivo imaging due to its 650nm-750nm emission range.