Il Yu

A Study on Correlation of Low Voltage Cathodoluminescent Properties with Electrical Conductivity of In2 O 3 ‐ Coated ZnGa2 O 4 : Mn Phosphors

The mechanism of enhancement on the low voltage cathodoluminescence (CL) efficiency by addition of In 2 O 3 in the phosphor particles has been investigated. The effect of In 2 O 3 coating by the sol-gel method on the CL of ZnGa 2 O 4 :Mn phosphors improves the luminance of low voltage CL noticeably. Especially it is observed that the emission intensity for the phosphor ZnGa 2 O 4 :Mn coated with 2 wt % In 2 O 3 is about four times higher than the as-it-is (non-coated In 2 O 3 ). Contrary to low voltage CL, the photoluminescence intensity of In 2 O 3 -coated ZnGa 2 O 4 :Mn phosphors decreases with an increase in In 2 O 3 coating wt %. It is shown by Rutherford backscattering study that the surface distribution of In 2 O 3 on In 2 O 3 -coated ZnGa 2 O 4 :Mn phosphors is islandlike but not intermediate-like (islands on a uniform layer). Also, investigations performed on the electrical conductivity of the phosphor screen prove the In 2 O 3 -coated ZnGa 2 O 4 :Mn phosphor screen to be an insulator. From the present work, it is understood that In 2 O 3 in the phosphor particles probably act as the localized bridge in draining the accumulated charge on the phosphor surface down to the indium tin oxide substrate due to the formation of the localized electrically conductive channels.

Nanoscale continuous In 2 O 3 coating on phosphor particles for improved low-voltage cathodoluminescent properties

A nanoscale continuous coating of In 2 O 3 on phosphors for low-voltage display applications is proposed in which the electrical conductivity of phosphor screen plays a major role. The effect of In 2 O 3 coating by the sol-gel method on the cathodoluminescence (CL) of ZnGa 2 O 4 :Mn phosphors improves the intensity of low-voltage CL noticeably compared with that of In 2 O 3 mixing. It is understood that electrically conductive channels are formed by a much smaller amount of In 2 O 3 addition than that of In 2 O 3 mixing. Especially, based on transmission electron microscopy analysis, the formation of uniform nanoscale continuous In 2 O 3 layers on the phosphor surface was confirmed. Also, the structural and CL characterizations presented in this paper clearly demonstrate that the nanoscale encapsulation of In 2 O 3 layers on phosphors served as protective layers retarding the CL degradation introduced by the low-energy electron irradiation, which is critically important for the development of low-voltage display applications.

Investigation of the characteristic changes on SrTiO3:Pr,Al,Ga phosphors during low voltage electron irradiation

We have investigated the mechanism of degradation of the low voltage cathodoluminescence (CL) efficiency of SrTiO3:Pr,Al,Ga phosphors. Based on Auger electron spectroscopy and x-ray photoelectron spectroscopy study, it is understood that prolonged irradiation of the phosphor with an electron beam of low voltage and high current density causes characteristic changes [(1) accumulation of overlying carbon and (2) reduction of oxygen] to occur on the phosphor surface. These changes are responsible for the rapid degradation of low voltage CL of SrTiO3:Pr,Al,Ga phosphors. The two aforementioned changes are shown to impact CL output in an important way. An accurate accounting of the total impact of the two changes warrants assessment of the importance of other degradation mechanisms. These other degradation mechanisms include both carbon- and noncarbon-related enhanced nonradiative electron-hole recombination at surfaces.

A Study on the Degradation of Cathodoluminescence of SrTiO3 : Pr , Al , Ga Phosphors Tailored for Low Voltage Display Applications

The mechanism of degradation on the low voltage cathodoluminescence (CL) efficiency of SrTiO 3 :Pr,Al,Ga phosphors is investigated. The effect of carbon overlayer adsorbed on the phosphor surface from the vacuum ambient during the electron irradiation done in a high vacuum chamber causes a rapid degradation of low voltage CL noticeably. Especially, based on Auger electron spectroscopy combined with CL spectroscopy it is observed that there is obvious correlation between carbon buildup and loss of CL brightness of the phosphors characterized in this study. Also, it is shown that the increased amount of carbon adsorbed during the electron irradiation on the SrTiO 3 :Pr,Al,Ga phosphor surface is completely removed by heating the degraded SrTiO 3 :Pr,Al,Ga samples at 470°C for 30 min in air. Furthermore, the decreased CL intensity of degraded samples is recovered up to that of original ones together with the removal of carbon. From the present work, it is understood that the rapid degradation of low voltage CL of the SrTiO 3 :Pr,Al,Ga phosphors is directly related to the formation of the carbon overlayer, but not related to a change in the emission properties of the luminescent center themselves.

Effect of the Particle Size of SnO 2 :Ni on Gas Sensing Properties

Ni 8 wt.%-doped tin oxide () thick films were fabricated into gas sensors by the method of screen printing onto alumina substrates. The particle size of was controlled by changing the ball-mill time between 0~120 h. The structural and morphological properties of these thick films were investigated using X-ray diffraction and scanning electron microscopy. The structural properties of powders showed a tetragonal phase with (110) dominant orientation. The particle size of the :Ni powders after ball-mill of 120 h was about 0.05 . The gas sensitivity (S

Characteristics of Thick Film Gas Sensors Using Nano ZnO:CNT

Abstract The effects of an addition of CNT on the sensing properties of nano ZnO:CNT-based gas sensors were studied forH 2 S gas. The nano ZnO sensing materials were grown by a hydrothermal reaction method. The nano ZnO:CNT was preparedby ball-milling method. The weight range of the CNT addition on the ZnO surface was from 0 to 10 %. The nano ZnO:CNTgas sensors were fabricated by a screen-printing method on alumina substrates. The structural and morphological properties ofthe ZnO:CNT sensing materials were investigated by XRD, EDS, and SEM. The XRD patterns revealed that nano ZnO:CNTpowders with a wurtzite structure were grown with (1 0 0), (0 0 2), and (1 0 1) dominant peaks. The size of the ZnO wasabout 210 nm, as confirmed by SEM images. The sensitivity of the nano ZnO:CNT-based sensors was measured for 5 ppmof H 2 S gas at room temperature by comparing the resistance in air with that in target gases.Key wordsZnO, CNT, H 2 S, ball-mill. 1. 서 론 산업 발전과 더불어 대기오염 문제로 인해 여러 가지가연성 가스와 유독성 가스 등을 감지하기 위한 가스센서의 필요성이 증가하고 있다. 현재, 가스 센서는 사용 목적과 감지 대상에 따라 다양한 종류가 개발되고 있다.

Response Characteristics of Thick Film Sensors Using Nano ZnO:Ni for Hydrocarbon Gas

The effects of a Ni coating on the sensing properties of nano ZnO:Ni based gas sensors were studied for and gases. Nano ZnO sensing materials were prepared by the hydrothermal reaction method. The Ni coatings on the nano ZnO surface were deposited by the hydrolysis of zinc chloride with . The weight % of Ni coating on the ZnO surface ranged from 0 to 10 %. The nano ZnO:Ni gas sensors were fabricated by a screen printing method on alumina substrates. The structural and morphological properties of the nano ZnO : Ni sensing materials were investigated by XRD, EDS, and SEM. The XRD patterns showed that nano ZnO : Ni powders with a wurtzite structure were grown with (1 0 0), (0 0 2), and (1 0 1) dominant peaks. The particle size of nano ZnO powders was about 250 nm. The sensitivity of nano ZnO:Ni based sensors for 5 ppm gas and gas was measured at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity of the ZnO:Ni sensor to gas and gas was observed at Ni 4 wt%. The response and recovery times of 4 wt% Ni coated ZnO:Ni gas sensors were 14 s and 15 s, respectively.

Gas Sensing Characteristics of Nano Sized SnO 2 Sensors for Various Co and Ni Concentration

Nano-sized SnO2 thick films were prepared by a screen-printing method onto Al2O3 substrates. The sensing characteristics were investigated by measuring the electrical resistance of each sensor in a test box as a function of the detection gas. The nano-sized SnO2 thick film sensors were treated in a N2 atmosphere. The structural properties of the nano SnO2 with a rutile structure according to XRD showed a (110) dominant SnO2 peak. The particle size of SnO2:Ni nano powders at Ni 8 wt% was about 45 nm, and the SnO2 particles were found to contain many pores according to the SEM analysis. The sensitivity of the nano SnO2-based sensors was measured for 5 ppm CH4 gas and CH3CH2CH3 gas at room temperature by comparing the resistance in air with that in the target gases. The results showed that the best sensitivity of SnO2:Ni and SnO2:Co sensors for CH4 gas and CH3CH2CH3 gas at room temperature was observed in SnO2:Ni sensors doped with 8 wt% Ni. The response time of the SnO2:Ni gas sensors was 10 seconds and recovery time was 15 seconds for the CH4 and CH3CH2CH3 gases.

Effect of ZnS:Mn, Dy Yellow Phosphor on White LEDs Characteristics

Abstract ZnS:Mn, Dy yellow phosphors for White Light Emitting Diode were synthesized by a solid state reaction methodusing ZnS, MnSO 4 ·5H 2 O, oS and DyCl 3 ·6H 2 O powders as starting materials. The mixed powder was sintered at 1000C for 4h in an air atmosphere. The photoluminescence of the ZnS:Mn, Dy phosphors showed spectra extending from 480 to 700 nm,peaking at 580 nm. The photoluminescence of 580 nm in the ZnS:Mn, Dy phosphors was associated with 4 T 1 → 6 A 1 transitionof Mn 2+ ions. The highest photoluminescence intensity of the ZnS:Mn, Dy phosphors under 450 nm excitation was observedat 4 mol% Dy doping. The enhanced photoluminescence intensity of the ZnS:Mn, Dy phosphors was explained by energytransfer from Dy 3+ to Mn 2+ . The CIE coordinate of the 4 mol% Dy doped ZnS:Mn, Dy was X = 0.5221, Y = 0.4763. Theoptimum mixing conditions for White Light Emitting Diode was obtained at the ratio of epoxy : yellow phosphor = 1:2 formCIE coordinate.Key wordsZnS, luminescence, Mn, Dy, LED.

Luminescent Characteristics of Bi Co-doped ZnS:Mn Yellow Phosphors for White Light Emitting Diodes

Abstract Bi co-doped ZnS:Mn,Bi yellow phosphors for white light emitting diodes were prepared by the conventional solid-state reaction method. The optical and structural properties of ZnS:Mn,Bi phosphors were investigated by x-ray diffraction,scanning electro microscopy and photoluminescence. ZnS:Mn,Bi phosphors showed XRD patterns of hexagonal structure. Thephotoluminescence of ZnS:Mn,Bi phosphors showed spectra extending from 480 to 700 nm, peaking at 580 nm. Thephotoluminescence of 580 nm in the ZnS:Mn,Bi phosphors was associated with the 4T1 → 6A1 transition of the Mn2+ ions. Thehighest photoluminescent intensity of the phosphors under 405 nm and 450 nm excitation was obtained at Bi concentration of7 mol%. The optimum mixing conditions with epoxy and yellow phosphor for white light emitting diodes were observed in aratio of epoxy:yellow phosphor of 1:3.5. The CIE chromaticity of the white LED at the 1:3.5 ratio was X = 0.3454 and Y = 0.2449.Key wordsZnS, Luminescence, Mn, Bi, LED.