Jumpei Ueda

Y3Al5O12(YAG):Ce3+ is the most widely applied phosphor in white LEDs (w-LEDs) because of strong blue absorption and efficient yellow luminescence combined with a high stability and thermal quenching temperature, required for the extreme operating conditions in high-power w-LEDs. The high luminescence quenching temperature (∼600 K) has been well established, but surprisingly, the mechanism for temperature quenching has not been elucidated yet. In this report we investigate the possibility of ther

Photocurrent excitation spectra were measured to investigate the quenching in the garnet solid solutions. Intense photocurrent excitation bands attributed to the lowest 5d(1) and the second lowest 5d(2) levels were observed in the Ce-doped Y(3)Al(2)Ga(3)O(12) (Ce:YAGG) and Y(3)Ga(5)O(12) (Ce:YGG). Based on the results of temperature dependence of photoconductivity, the 5d(1) and 5d(2) levels in the Ce:YAGG are found to be located below and within the conduction band, respectively, while both lev

Charging efficiency by blue light and trap depth were controlled <italic>via</italic> conduction band engineering in Y₃Al_5−xGa_xO₁₂:Ce³⁺–Cr³⁺.

In Ce3+–Yb3+ co-doped Y3Al5O12 (YAG) ceramics, possibility of quantum cutting mechanism converting one visible photon into two NIR photons with optimum quantum efficiency approaching 200% have been investigated. In this material, Yb3+ emissions due to the F25/2-F27/2 in the range of 1 μm were observed upon the excitation of 5d level of Ce3+. In addition, excitation spectra of Yb3+ emission corresponded to that of Ce3+ emission completely. Lifetime of the 5d level of Ce3+ decreased with increasin

We have developed bright persistent phosphors of Ce3+-Cr3+-doped Y3Al5-xGaxO12 (x = 2.5, 3, 3.5) ceramics with green luminescence (Ce3+:5d→4f) via blue-light excitation. The persistent luminance value 5 min after ceasing blue-light excitation for the Ce3+-Cr3+-doped Y3Al2Ga3O12 sample is approximately 3900 times higher than that for a Ce3+-doped Y3Al2Ga3O12 sample and better than that from compact SrAl2O4:Eu2+-Dy3+ powders. The results are consequences of efficient carrier trap formation and eff

The Y₃Al₂Ga₃O₁₂:Ce³⁺-Cr³⁺ compound is one of the brightest persistent phosphors, but its persistent luminescence duration is not so long because of the relatively shallow Cr³⁺ electron trap. To compare the vacuum referred binding energy of the electron trapping state by Cr³⁺ and lanthanide ions, we selected Yb³⁺ as a deeper electron trapping center. The Y₃Al₂Ga₃O<su

The absorption and luminescence properties (centroid shift and crystal field splitting of 5d orbitals) of Ce3+-doped garnets are summarized from the viewpoints of chemical composition (electron negativity and optical basicity) and the local crystal structure of the Ce3+ ion (bond length and distortion). Clear trends exist between (1) the centroid shift of 5d energy (εc) and the optical basicity of the host garnets and between (2) the crystal field splitting of the lowest 5d1-5d2 levels (Δ12) and

We investigated thermally activated ionization and thermally activated crossover as the two possibilities of quenching of $5d$ luminescence in $\mathrm{P}{\mathrm{r}}^{3+}$-doped ${\mathrm{Y}}_{3}\mathrm{A}{\mathrm{l}}_{5\ensuremath{-}x}\mathrm{G}{\mathrm{a}}_{x}{\mathrm{O}}_{12}$. Varying the Ga content $x$ gives the control over the relative energy level location of the $5d$ and $4{f}^{2}:^{3}P_{J}$ states of $\mathrm{P}{\mathrm{r}}^{3+}$ and the host conduction band (CB). Temperature-dependen

We have developed a yellow persistent phosphor of Ce3+–Cr3+-codoped Gd3Al2Ga3O12 transparent ceramics prepared by a solid-state reaction. The yellow persistent luminescence due to the Ce3+: 5d–4f transition was observed even after 460 nm blue-light excitation as well as after UV excitation. The chromaticity coordinate of the persistent luminescence in the ceramic phosphor is located at , which appears really yellow compared with the color coordinate of the well-known SrAl2O4:Eu2+–Dy3+ or other c

We report near-infrared persistent luminescence and photochromism in Eu2+-Nd3+-codoped CaAl2O4 ceramics, a well-known blue persistent phosphor. After irradiation with UV light, the color of the sample body changed from white to purple. From the reflectance spectrum, the color center created by UV irradiation has a broad absorption band at 500 nm, which results in pink coloration. The purple color of the sample just after stopping UV irradiation is caused by mixing the blue persistent luminescenc

We report on long-lasting afterglow phosphorescence at around 500 nm in Ce3+-doped yttrium scandium gallium garnet (YSGG) ceramics with the composition of (Y0.995Ce0.005)3Sc2Ga3O12 prepared by solid-state reaction at 1600 °C. The afterglow luminescence was observed for 1 h after the 440 nm excitation in the Ce:YSGG ceramic prepared under vacuum. However, the afterglow decay time decreased after O2 annealing. Therefore, one of the potential traps can be oxygen vacancies. Based on the correlation

Abstract CaAlSiN3:Eu2+ is a widely applied phosphor in white LEDs (w-LEDs) because of strong blue absorption and efficient red luminescence with high thermal quenching temperature. The good stability against thermal quenching has been well established, but the mechanism for the luminescence quenching at high temperatures has not been elucidated yet. In this report, we investigate the possibility of thermal ionization quenching by thermoluminescence (TL) and persistent luminescence techniques. In