Abstract The discovery of inorganic phosphors that can be excited by GaN light emitting diodes in the wavelength range 380–460 nm is essential for improving the efficiency and light quality of solid state lighting devices. Garnets doped with Ce 3+ are of particular interest for this application. We have studied the luminescence of Ce 3+ in garnet phosphors and established a relationship between the excitation/emission wavelengths and the deviation from cubic symmetry around the rare-earth ion. Data are presented for both known yttrium aluminum and yttrium gallium garnet systems, as well as newly synthesized inverse garnets of the general formula Mg 3 Y 2− y Gd y Ge 3− z Si z O 12 :Ce (0 ⩽  y  ⩽ 2, z  = 0, 1).

http://ma.ecsdl.org/content/MA2007-02/33/1520.full.pdf

Structure-Property Correlations in Ce-Doped Garnet Phosphors for Use in Solid State Lighting

Laser excitation and x-ray spectroscopy are combined to settle a long-standing question in persistent luminescence. A reversible electron transfer is demonstrated, controlled by light and showing the same kinetics as the persistent luminescence. Exposure to violet light induces charging by oxidation of the excited Eu^{2+} while Dy^{3+} is simultaneously reduced. Oppositely, detrapping of Dy^{2+} occurs at ambient temperature or by infrared illumination, yielding afterglow or optically stimulated luminescence, respectively.

https://biblio.ugent.be/publication/8671667/file/8671669.pdf

Identification of Dy^{3+}/Dy^{2+} as Electron Trap in Persistent Phosphors

Functional phosphors with shortwave infrared (SWIR) persistent luminescence have attracted an ever-increasing interest from scientists owning to the self-sustainable emission for deeper tissue pene...

Ni2+-Doped Yttrium Aluminum Gallium Garnet Phosphors: Bandgap Engineering for Broad-Band Wavelength-Tunable Shortwave-Infrared Long-Persistent Luminescence and Photochromism

Rechargeable and sunlight-activated Sr3Y2Ge3O12:Bi3+ UV–Visible-NIR persistent luminescence material for night-vision signage and optical information storage

The ${F}^{+}$ center consisting of an electron trapped at an oxygen vacancy (${V}_{\mathrm{O}}$) was investigated in oxygen deficient ${\mathrm{Y}}_{3}{\mathrm{Al}}_{5}{\mathrm{O}}_{12}$ (YAG) garnet crystals by electron paramagnetic resonance (EPR) techniques. The measurements were performed in the wide temperature interval 5--450 K and the frequency range 9.4--350 GHz using both the conventional continuous-wave and pulse EPR experiments. Pulse electron-nuclear double resonance was applied to resolve the hyperfine interaction of the trapped electron with surrounding nuclei. The measurements show that at low temperatures, $Tl50$ K, the EPR spectrum of the ${F}^{+}$ center is anisotropic with $g$ factors in the range 1.999--1.988 and originates from three magnetically inequivalent positions of the center in a garnet lattice. As the temperature increases, the EPR spectrum becomes isotropic suggesting a motional averaging of the anisotropy due to motion of the ${F}^{+}$-center electron between neighboring oxygen vacancies. With further increase of temperature up to $T$ g 200 K, we observed delocalization of the ${F}^{+}$-center electron into the conduction band with the activation energy about 0.4--0.5 eV that resulted in substantial narrowing of the EPR spectral line with simultaneous change of its shape from Gaussian to Lorentzian due to disappearance of the Fermi contact hyperfine field at $^{27}\mathrm{Al}$ and $^{89}\mathrm{Y}$ nuclei. Such temperature behavior of the ${F}^{+}$-center electron in YAG is completely similar to behavior of a donor electron in a semiconductor. Our findings are further supported by measurements of the conductivity and dielectric properties. In particular, these data show that the electrons in the conduction band are not homogeneously distributed in the crystal: There are highly conductive regions separated by poorly conductive dielectric layers. This leads to the so-called Maxwell-Wagner dielectric relaxation with huge apparent dielectric constant at low frequencies. This paper reports an observation of a donorlike behavior of an ${F}^{+}$ center in wide band-gap insulating crystals.

Oxygen-vacancy donor-electron center in Y 3 Al 5 O 12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

Control of optical properties of YAG crystals by thermal annealing

This paper addresses the carbon co-doping of Ce-doped garnets, an efficient scintillation material and white light phosphor. The composition and the optical and scintillation properties of carbon-c...

Impact of Carbon Co-Doping on the Optical and Scintillation Properties of a YAG:Ce Scintillator

/pdf/drastic-scintillation-yield-enhancement-of-yag-ce-with-39gn4mut1q.pdf

Drastic Scintillation Yield Enhancement of YAG:Ce with Carbon Doping

The work is motivated by the need for cheap garnet-based scintillators for new high energy physics experiments at colliders and medical equipment. During recent years, garnets became among the most studied scintillators due to a drastic enhancement of light yield achieved in (Lu,Y,Gd)3(Al,Ga)5O12:Ce multicomponent systems. Meanwhile, the production process of YAG- and LuAG-based crystals is easier and less expensive compared to the multicomponent garnets. This work addresses the preparation process and the optical and scintillation properties of YAG, YAG:Ce crystals grown in non-precious metal crucibles.

P. Arhipov

Papers

Oxygen-vacancy donor-electron center in Y 3 Al 5 O 12 garnet crystals: Electron paramagnetic resonance and dielectric spectroscopy study

Control of optical properties of YAG crystals by thermal annealing

Impact of Carbon Co-Doping on the Optical and Scintillation Properties of a YAG:Ce Scintillator

Drastic Scintillation Yield Enhancement of YAG:Ce with Carbon Doping

Garnet Crystal Growth in Non-precious Metal Crucibles