• Journal of the Korean Vacuum Society
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• v.22 no.6
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• pp.291-297
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• 2013

ZnO nanowires were synthesized by vapor-liquid-solid (VLS) process using ZnO and graphite powders on the sapphire substrate coated with an Au film as a catalyst. ZnO nanowires had two prominent emission bands; i) near-band edge (NBE) emission band at 380 nm, and ii) a relatively stronger deep level (DL) emission band ($I_{NBE}/I_{DL}$ <1). In order for the ZnO nanowires to be utilized as an effective material for UV emitting devices, the photoluminescence intensity of NBE needs to be improved with the decreased intensity of DL. In the current study, hydrogen plasma treatment was performed to improve the photoluminescence characteristics of ZnO nanowires. With the hydrogen plasma treatment time of more than 120 sec, the extent of performance improvement was gradually decreased. However, the intensity ratio of NBE to DL ($I_{NBE}/I_{DL}$) was significantly improved to about 4 with a relatively short plasma treatment time of 90 sec, suggesting hydrogen plasma treatment is a promising approach to improve the photoluminescence properties of ZnO nanowires.

• Macromolecular Research
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• v.11 no.2
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• pp.92-97
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• 2003

Model compounds and polymers having N-substituted 1,2-diphenylmaleimide moieties were synthesized and characterized by NMR, IR, UV, and fluorescence spectroscopy. The fluorescence intensity could be controlled by N-substituents of model compounds and polymers. As the structure of an N-substituent of them was bulkier, or the electron density of an N-substituent was denser, the photoluminescence intensity was increased. All the compounds showed greenish yellow photoluminescence with the maximum intensity between 510 and 537 nm. From quantum efficiency data of the model compounds and the polymers, the fluorescence intensity of the polymer 11 was higher than that of the model compound 4.

• Transactions on Electrical and Electronic Materials
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• v.11 no.4
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• pp.170-173
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• 2010

Nanocrystalline cadmium sulfide (CdS) thin films were prepared using chemical bath deposition in a solution bath containing $CdSO_4$, $SC(NH_2)_2$, and $NH_4OH$. The CdS thin films were investigated using X-ray diffraction (XRD), photoluminescence (PL), and Fourier transform infrared spectroscopy (FTIR). The as-deposited CdS thin film prepared at $80^{\circ}C$ for 60 min had a cubic phase with homogeneous and small grains. In the PL spectrum of the 2,900 A-thick CdS thin film, the broad red band around 1.7 eV and the broad high-energy band around 2.7 eV are attributed to the S vacancy and the band-to-band transition, respectively. As the deposition time increases to over 90 min, the PL intensity from the band-to-band transition significantly increases. The temperature dependence of the PL intensity for the CdS thin films was studied from 16 to 300 K. The $E_A$ and $E_B$ activation energies are obtained by fitting the temperature dependence of the PL intensity. The $E_A$ and $E_B$ are caused by the deep trap and shallow surface traps, respectively. From the FTIR analysis of the CdS thin films, a broad absorption band of the OH stretching vibration in the range $3,000-3,600\;cm^{-1}$ and the peak of the CN stretching vibration at $2,000\;cm^{-1}$ were found.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.23 no.8
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• pp.627-631
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• 2010

ZnS:Mn yellow phosphors doped with Cu for white light emitting diodes were synthesized by solid state reaction method. The optical properties and structures of ZnS:Mn,Cu phosphors were investigated by x-ray diffraction, photoluminescence, and scanning electro microscopy. Photoluminescence excitation spectra originated from $Mn^{2+}$ were ranged from 450 nm to 500 nm. The yellow emission at around 580 nm was associated with $^4T_1{\rightarrow}^6A_1$ transition of $Mn^{2+}$ ions in ZnS:Mn,Cu phosphors. The highest photoluminescence intensity of the phosphors under 405 nm excitation was obtained at Cu concentration of 0.02 mol%. The enhanced photoluminescent intensity in the ZnS:Mn,Cu phosphors was interpreted by energy transfer from Cu to Mn.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1083-1086
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• 2004

We applied the spray pyrolysis technique to prepare Mn-doped $BaMgAl_{10}O_{17}$ (BAM) particles with high photoluminescence, which could be used in the plasma display device as a green phosphor. Several preparation conditions were investigated in order to tail the vacuum ultraviolet (VUV) characteristics. Some portions of barium were replaced with strontium to improve the luminescent intensity of BAM:Mn particles under VUV excitation. The content of Mn and Sr was optimized to obtain high luminescent efficiency under VUV excitation. Finally, the optimized BAM:Mn green particles showed higher photoluminescence intensity than that of commercial $Zn_2SiO_4$ and comparable with commercial barium-aluminate phosphor.

• Journal of Surface Science and Engineering
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• v.45 no.5
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• pp.193-197
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• 2012

The influence of annealing process in an $O_2$ atmosphere on the photoluminescence (PL) spectra properties of ZnS nanowires has been investigated. ZnS nanowires with the diameters approximately 100 nm and the lengths a few tens micrometers were synthesized by evaporating ZnS powders on Si substrates while using an Au thin film as a catalyst. ZnS nanowires had an NBE emission band at 430 nm in the violet region. The emission intensity was improved drastically by a process in which ZnS nanowires were heat-treated at $500^{\circ}C$ in an $O_2$ atmosphere for 45 minutes.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.443-449
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• 2018

We investigated the temperature-dependent photoluminescence spectroscopy of colloidal InZnP/ZnSe/ZnS (core/shell/shell) quantum dots with varying ZnSe and ZnS shell thickness in the 278~363 K temperature range. Temperature-dependent photoluminescence of the InZnP-based quantum dot samples reveal red-shifting of the photoluminescence peaks, thermal quenching of photoluminescence, and broadening of bandwidth with increasing temperature. The degree of band-gap shifting and line broadening as a function of temperature is affected little by shell composition and thickness. However, the thermal quenching of the photoluminescence is strongly dependent on the shell components. The irreversible photoluminescence quenching behavior is dominant for thin-shell-deposited InZnP quantum dots, whereas thick-shelled InZnP quantum dots exhibit superior thermal stability of the photoluminescence intensity.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.531-535
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• 1996

ZnGa2O4 and Mn-doped ZnGa2O4 were synthesized using the state reaction method to investigate their photoluminescence characteristics depending on Mn concentration. Under 254nm excitation, ZnGa2O4 exhibited a broad-band emission extending from 330 nm to 610 nm peaking at 450nm. On the other hand Mn-doped ZnGa2O4 showed a new strong narrow-band emission peaking at 504 nm and maximum intensity at the doping concentration of 0.006 mole Mn.

• Applied Chemistry for Engineering
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• v.26 no.3
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• pp.362-365
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• 2015

Silica encapsulated ZnSe quantum dots (QDs) were prepared by employing two microemulsion systems: AOT/water/cyclohexane microemulsions containing ZnSe quantum dots with NP5/water/cyclohexane microemulsions containing tetraethylorthosilicate (TEOS). Using this method, cubic zinc blende nanoparticles (3 nm in diameter) were synthesized and encapsulated by silica nanoparticles (20 nm in diameter). The temperature dependence of photoluminescence (PL) for silica-encapsulated ZnSe QDs was investigated to evaluate this material as a temperature sensor media. The fluorescence emission intensity of silica-encapsulated ZnSe nanoparticles (NPs) was decreased with an increase of ambient temperature over the range from $30^{\circ}C$ to $60^{\circ}C$ and a linear relationship between the temperature and the emission intensity was observed. In addition, the temperature dependence of PL intensity for silica-encapsulated ZnSe NPs showed a reversible pattern on ambient temperature. A reversible temperature dependence of the luminescence combined with its insensitivity toward quenching by oxygen due to silica coating established this material as an attractive media for temperature sensor applications.

• Journal of Ceramic Processing Research
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• v.20 no.1
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• pp.80-83
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• 2019

The Mn4+-activated Li2ZnSn2O6 (LZSO:Mn4+) red phosphors were synthesized by the solid-state reaction at temperatures of 1100-1400 ℃ in air. The synthesized LZSO:Mn4+ phosphors were confirmed to have a single hexagonal LZSO phase without the presence of any secondary phase formed by the Mn4+ addition. With near UV and blue excitation, the LZSO:Mn4+ phosphors exhibited a double band deep-red emission peaked at ~658 nm and ~673 nm due to the 2E → 4A2 transition of Mn4+ ion. PL emission intensity showed a strong dependence on the Mn4+ doping concentration and the 0.3 mol% Mn4+-doped LZSO phosphor produced the strongest PL emission intensity. Photoluminescence emission intensity was also found to be dependent on the calcination temperature and the optimal calcination temperature for the LZSO:Mn4+ phosphors was determined to be 1200 ℃. Dynamic light scattering (DLS) and field-effect scanning electron microscopy (FE-SEM) analysis revealed that the 0.3 mol% Mn4+-doped LZSO phosphor particles have an irregularly round shape and an average particle size of ~1.46 ㎛.