Dissertation > Industrial Technology > Radio electronics, telecommunications technology > Semiconductor technology > Semiconductor diode > Diodes: structure and performance > Light-emitting diodes

Design,Preparation and Properties of Oxynitrides Luminance Material

Author MaYanYan
Tutor JiangZhongHong
School South China University of Technology
Course Materials Science
Keywords oxynitrides rare-earth ion phosphor light-emitting-diode
CLC TN312.8
Type PhD thesis
Year 2013
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Phosphor-converted white light-emitting diodes (pc-WLEDs) are emerging as anindispensable solid-state light source for the next generation lighting industry and displaysystems due to their unique properties such as energy saving, environment-friendly, smallvolume and long persistence. Generally, the brightness, color rending index, and stability ofWLEDs strongly depend on the quality of phosphors. The development of efficient phosphormaterials with high chemical and temperature stability, high efficiency and no environmentalhazards is desirable for applications in WLEDs. Furthermore, it is necessary for the phosphorsto absorb the NUV or blue light efficiently that is radiated from the GaN/InGaN-basedsemiconductor LED chips. The (oxy)nitride compounds have attracted greater attention due totheir superior thermal, chemical stability and their structural diversity over the past severalyears.(1) A blue-emitting Si3N4:Ce3+phosphor is synthesized by solid-state reaction in H2/N2reductive atmosphere by adding MgO. The series of Si3N4:Ce3+phosphors are efficientlyexcited at wavelengths ranging from260to380nm, which can match well with ultraviolet(UV) light emitting diodes (LEDs) chip. Under340nm light irradiation, Si3N4:Ce3+exhibitsbroad blue emission. In addition, it is found that MgO addition play important roles onenhancement of luminescence properties.(2) Tervalent cerium ions (Ce3+)-doped oxonitridosilicate compound Y2Si3O3N4wereprepared by solid-state reaction method in a reduced atmosphere using NH4Cl as flux. Theeffects of Ce3+doping concentrations and NH4Cl flux on structural and luminescent propertiesof the Y2Si3O3N4phosphors were investigated in detail. The phosphors showed intenseabsorption in near ultraviolet (NUV) region and exhibited bright blue emission with tunableCommission Internationale de l’Eclairage (CIE) coordinates. The Y2Si3O3N4:Ce3+samplesshowed a broad emission band with peak wavelength ranging from465to500nm, which wasattributed to the5d-4f transition of Ce3+. Energy transfer between Ce3+ions was discussed andevidenced in detail, which resulted in redshift of the emission and concentration quenching.To understand the thermal quenching behavior, the temperature-dependent luminescence ofY1.94Ce0.06Si3O3N4was investigated. Bluish-green LEDs was fabricated by integrating anear-ultraviolet (NUV) chip with Y1.94Si3O3N4:0.06Ce3+phosphor as a single package.(3) CaSi2O2N2:Eu2+phosphors with zinc acetate additive as a flux agent have beensynthesized by solid state process. The structure, morphology and photoluminescence (PL)properties of the compounds are investigated as a function of zinc acetate dihydrate (Zn(CH3COO)2·2H2O) dosage. A strong absorption band from near ultraviolet (NUV) tovisible range and a broad yellow emission band in the wavelength range of460-700nm areobserved in Eu2+doped CaSi2O2N2. The sheet-like morphology sample transforms into blockas Zn(CH3COO)2·2H2O content reaching43wt%, associated with increasing emissionintensity. High-intensity yellowish light emitting diode is obtained by combiningCaSi2O2N2:Eu2+as the wavelength conversion phosphor with NUV InGaN LED-chip.(4) LiSiON:Eu2+, Mn2+phosphors were fabricated using Li4SiO4:Eu2+, Mn2+and Si3N4as starting materials. The crystal and electronic structures, as well as the luminescenceproperties of LiSiON:Eu2+, Mn2+were reported. First-principles calculations indicated thatLiSiON host was an insulator with indirect band gap about5.4eV, which was in goodagreement with the experimental data obtained from the diffuse reflection spectrum. Theconcentration of Eu2+in LiSiON:Eu2+gave rise to obvious differences in the emission profilesand peak wavelength which might result from the different crystal environments around Eu2+ions. The mechanism of energy transfer from a sensitizer Eu2+ion to an activator Mn2+ion inLiSiON:Eu2+,Mn2+phosphors were demonstrated to be electric dipole-quadrupole interaction.The emission hue of LiSiON:Eu2+, Mn2+varied from blue to white-light by tuning the Eu2+and Mn2+ratio.

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