• Journal of the Korean Crystal Growth and Crystal Technology
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• v.17 no.5
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• pp.204-209
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• 2007

We synthesized a series of $CaS_{1-x}Se_x:Eu$ red-emitting phosphors for application in phosphor-converted three-band white light emitting diode(LED). The photoluminescence and structural properties of $CaS_{1-x}Se_x:Eu$ were examined. The $CaS_{1-x}Se_x:Eu$ phosphors have a strong absorption at 455 nm, which is the emission wavelength of a blue LED. CaS:Eu has a red omission peak at 651 nm due to the $4f^65d^1(T_{2g}){\rightarrow}4f^7(^8S_{7/2})$ transition of the $Eu^{2+}$. The emission peak of $CaS_{1-x}Se_x:Eu$ is shifted from 651 to 598 nm with increasing Se content. $CaS_{1-x}Se_x:Eu$ can be used as wavelength-tunable red-emitting phosphors pumped by a blue LED. We also fabricated a three-band white LED by doping $SrGa_2S_4:Eu$ and $CaS_{0.50}Se_{0.50}:Eu$ phosphors onto a blue LED chip.

• Bulletin of the Korean Chemical Society
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• v.30 no.2
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• pp.419-422
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• 2009

The luminescence intensity of calcium sulfide codoped with $Eu^{2+},\;Si^{4+}\;and\;Ga^{3+}$ was investigated as a function of the dopant concentration. An enhancement of the red luminescence resulted from the incorporation of $Si^{4+}\;and\;Ga^{3+}\;into\;CaS:Eu^{2+}.\;The\;non-codoped\;CaS:Eu^{2+}$ converted only 3.0% of the absorbed blue light into luminescence. As the $Si^{4+}\;and\;Ga^{3+}$ were embedded into the host lattice, the luminescence intensity increased and reached a maximum of Q = 10.0% at optimized concentrations of the codopants in CaS. Optimized CaS:$Eu^{2+},Si^{4+},Ga^{3+}$ phosphors were fabricated with blue GaN LED and the chromaticity index of the phosphor-formulated GaN LED was investigated as a function of the wt% of the optimized phosphor.

• Bulletin of the Korean Chemical Society
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• v.29 no.4
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• pp.822-826
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• 2008

We report the cathodoluminescence and aging properties of a series of green phosphors of formula $Sr_{1-x}M_xGa_2S_4$:Eu (x = 0.0-1.0, M = Ba or Ca) that have potential applications in field emission displays (FEDs). The series of phosphors was synthesized via NaBr-aided solid-state reactions in a flowing $H_2S$ stream. A low level ($\sim$20%) of Ba or Ca substitution for Sr in $SrGa_2S_4$:Eu maintains the orthorhombic phase of pure $SrGa_2S_4$:Eu phosphors. Further, a low level ($\sim$20%) of Ba or Ca substitution for Sr in $SrGa_2S_4$:Eu provides various green colors and sufficient brightness for FED applications. Substitution of Ba or Ca for Sr in $SrGa_2S_4$:Eu also improved the stability of the phosphor when it was operated under electron-beam irradiation of 5 kV.

• Bulletin of the Korean Chemical Society
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• v.28 no.8
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• pp.1280-1284
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• 2007

A series of Ca1-xSrxS:Eu (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) phosphors were synthesized by solid-state reactions. The Ca1-xSrxS:Eu phosphors have a strong absorption at 455 nm, which corresponds to the emission wavelength of a blue LED. The emission peak of Ca1-xSrxS:Eu is blue shifted from 655 to 618 nm with increasing Sr content. The characteristics of Ca1-xSrxS:Eu phosphors make them suitable for use as wavelengthtunable red-emitting phosphors for three-band white LEDs pumped by a blue LED. In support of this, we fabricated a three-band white LED by coating SrGa2S4:Eu and Ca0.6Sr0.4S:Eu phosphors onto a blue LED chip, and characterized its optical properties.

• Electrical & Electronic Materials
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• v.8 no.6
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• pp.752-758
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• 1995

Red emitting CaS:Eu,S electroluminescent(EL) device prepared at 550.deg. C by an electron-beam evaporation technique, demonstrated luminance of 175cd/m$\^$2/ and efficiency of 0.311m/W with 3kHz drive. Luminance was increased with the increase of applied voltage and frequency. From the results of the PL spectrum and the EL spectrum, the CaS:Eu, S device showed emission peak near 640nm resulted from the transition of EU$\^$2+/ 4f$\^$6/5d.rarw.4f$\^$7/. The capacitance of the phosphor layer from the Sawyer-Tower circuit was 10.5nF/cm$\^$2/.

• Journal of Sensor Science and Technology
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• v.8 no.5
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• pp.388-393
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• 1999

In this study, the $CaSO_4:Eu$ TLDs are fabricated and their trap parameters are determined. The optimum concentration of Eu for fabrication of the $CaSO_4:Eu$ TLD is 0.5 mol% and optimum temperature is $600^{\circ}C$ for 2 hours sintering in air. The glow curve of $CaSO_4:Eu$ consists of two glow peaks and these peaks are isolated by thermal bleaching method. Trap parameters of two glow peaks are measured using the initial rise, the peak shape, the heating rate and the least square curve fitting methods. The activation energies of the glow peak I and II are 1.00 eV and 1.09 eV, and the frequency factors are $7.04{\times}10^{11}\;s^{-1}$ and $5.12{\times}10^{11}\;s^{-1}$ and the kinetic orders are 1.11 and 1.33, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 2009.10a
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• pp.1274-1275
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• 2009

We report on preparation of $CaBaSiS_4:Eu^{2+}$ material by an advanced chemical solution method and fluorescent properties of the new material. The emission spectrum of $CaBaSiS_4:Eu^{2+}$ has the main peak centered at 598 nm, with the corresponding excitation maximum at around 420 nm. The strongest emission intensity of this material approached 96% compared to one of the best commercially available YAG:$Ce^{3+}$ phosphor.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.307-308
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• 2006

We have synthesized $CaS:Eu^{2+}$ phosphor by using a sealing vessel and evaluated its photoluminescence properties. The method using a sealing vessel is simple and economical in comparison with other methods reported up to date, As an activator concentration was increased from 0.1 mol to 4 mol, the main emission wavelength of the phosphor was increased from 642 nm to 651 nm due to crystal field splitting of 5d level of $Eu^{2+}$ ions. Although the same amount of $Eu_2O_3$ was used, the concentration of the activator ions which were reduced from $Eu^{3+}$ to $Eu^{2+}$ and substituting $Ca^{2+}$ ions was increased with increase of firing temperature. Therefore, the main emission wavelength was also increased from 645 nm to 651 nm with increase of firing temperature from $1100^{\circ}C$ to $1300^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.44 no.3 s.298
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• pp.147-151
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• 2007

An improvement for the efficiency of the $Sr_{2}SiO_{4}:Eu$ yellow phosphor under the $450{\sim}470\;nm$ excitation range have been achieved by adding the co-doping element ($Mg^{2+}\;and\;Ba^{2+}$) in the host. White LEDs were fabricated through an integration of an blue (InGaN) chip (${\lambda}_{cm}=450\;nm$) and a blend of two phosphors ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) in a single package. The InGaN-based two phosphor blends ($Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor) LEDs showed three bands at 450 nm, 550 nm and 640 nm, respectively. The 450 nm emission band was due to a radiative recombination from an InGaN active layer. This 450 nm emission was used as an optical transition of the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor. As a consequence of a preparation of white LEDs using the $Mg^{2+},\;Ba^{2+}\;co-doped\;Sr_{2}SiO_{4}:Eu$ yellow phosphor+CaS:Eu red phosphor yellow phosphor and CaS:Eu red phosphor, the highest luminescence efficiency was obtained at the 0.03 mol $Ba^{2+}$ concentration. At this time, the white LEDs showed the CCT (5300 K), CRI (89.9) and luminous efficacy (17.34 lm/W).

• Transactions on Electrical and Electronic Materials
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• v.8 no.6
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• pp.255-259
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• 2007

We have synthesized $CaS:Eu^{2+}$ phosphor by using a sealing vessel and evaluated its photoluminescence properties. The method using a sealing vessel is simple and economical in comparison with other methods reported up to date. As an activator concentration was increased from 0.1 mol% to 4 mol%, the main emission wavelength of the phosphor was increased from 642 nm to 651 nm due to the crystal field splitting of 5d levels of $Eu^{2+}$ ion. Although the same amount of $Eu_2O_3$ was used, the concentration of the activator ions, which were reduced from $Eu^{3+}\;to\;Eu^{2+}$ and substituted $Ca^{2+}$ ions, was increased with increase of firing temperature. Therefore, the main emission wavelength was also. shifted from 645 nm to 651 nm with increase of firing temperature from $1100^{\circ}C\;to\;1300^{\circ}C$. The critical distance($R_{c1}=20.65\;{\AA}$) between $Eu^{2+}$ ions calculated from the critical concentration was well matched with that($R_{c2}=19.17\;{\AA}$) calculated from the Dexter formula.