In situ luminescence measurements of GaN/Al_(2)O_(3) film under different energy proton irradiations

Ion beam-induced luminescence(IBIL) experiments were performed to investigate the in situ luminescence of GaN/Al_(2)O_(3) at varying ion energies,which allowed for the measurement of defects at different depths within the material.The energies of H^(+)were set to 500 keV,640 keV and 2 MeV,the Bragg peaks of which correspond to the GaN film,GaN/Al_(2)O_(3) heterojunction and Al_(2)O_(3) substrate,respectively.A photoluminescence measurement at 250 K was also performed for comparison,during which only near band edge(NBE) and yellow band luminescence in the GaN film were observed.The evolution of the luminescence of the NBE and yellow band in the GaN film was discussed,and both exhibited a decrease with the fluence of H^(+).Additionally,the luminescence of F centers,induced by oxygen vacancies,and Cr^(3+),resulting from the ^(2)E →^(4)A_(2) radiative transition in Al_(2)O_(3),were measured using 2 MeV H^(+).The luminescence intensity of F centers increases gradually with the fluence of H^(+).The luminescence evolution of Cr^(3+)is consistent with a yellow band center,attributed to its weak intensity,and it is situated within the emission band of the yellow band in the GaN film.Our results show that IBIL measurement can effectively detect the luminescence behavior of multilayer films by adjusting the ion energy.Luminescence measurement can be excited by various techniques,but IBIL can satisfy in situ luminescence measurement,and multilayer structural materials of tens of micrometers can be measured through IBIL by adjusting the energy of the inducing ions.The evolution of defects at different layers with ion fluence can be obtained.

重离子在SiC,GaN,Ga_(2)O_(3)宽禁带半导体材料及器件中的辐照效应研究

针对近年来出现的新型宽禁带半导体材料和器件,介绍了SiC,GaN,Ga_(2)O_(3)材料和器件重离子辐照效应的一些研究成果:SiC材料对重离子辐照不敏感,但SiC器件在高压工作条件下易发生重离子单粒子效应;GaN材料有较好的抗低能重离子辐照特性,但对快重离子辐照,易发生辐照损伤,影响GaN器件性能;Ga_(2)O_(3)材料快重离子辐照下易发生结构损伤,影响Ga_(2)O_(3)器件性能。同时着重阐述了SiC器件重离子辐照响应特性与失效机理,以及GaN器件电学性能退化与材料结构损伤之间关系。

High pressure luminescence studies of europium doped GaN

We reported on the high pressure luminescence spectra of polycrystalline Eu-doped GaN material synthesized in the reaction between alloys of gallium, bismuth and europium in ammonia atmosphere. The integrated luminescence intensity of the dominant Eu3＋ ion transition （5D0→^7F2） at 622 nm increased approximately one order of rnagnitude whereas its spectral position and line width did not change significantly between ambient and 6.8 GPa pressure, respectively. Moreover, material was characterized with photo- and cathodo-luminescence, and photoluminescence excitation spectra at different temperatures. It was found that the Eu3＋ ions occupying substitutional Ga site created different centers which could be effectively excited with above band gap excitation and from excitons resonantly photoexcited at the I2 bound exciton energy. Furthermore, the less efficient Eu3＋ ions excitation path existed through intrinsic impurities and defeels generating shallow energy levels in the forbidden gap. It was proposed that reduction of the thermal quenching and consequent enhancement of Eu3＋ ion emission intensity resulted from stronger localization of bound exciton on RESI trap induced by applied pressure.

Investigation of Microenvironment-Depended Photoluminescence in Eu^(3+)-Implantation of GaN

GaN thin films grown on sapphire were implanted by Eu^3＋ with three different fluences （5.0×10~14 , 2.5×10~15 and 5.0×10~15cm~–2 ）. The photoluminescence （PL） spectra show that, after annealing, the samples exhibit strong emission at around 622.0 nm under 325 nm laser excitation. The intensity of this emission increases by one order of magnitude after annealing at from 600 ℃ to 900 ℃. Moreover, it increases less than 2 times when the fluence increases from 5×10~14 cm~–2 to 5×10~15 cm~–2 for the sample annealing at 900 ℃. The PL emission peaks around 622 nm of samples annealing at 900 ℃ can be well clarified by Gaussian fitting into 620.2, 622.0 and 625.0 nm, which are due to the Eu^3＋ related with defects, Eu^3＋ occupied at substitutional positions of Ga, and that located at interstitial sites, respectively. It shows that the different microenvironments and positions of Eu^3＋ are responsible for these peaks, and especially the defects introduced by implantation play an important role in the behavior of the PL because they set up an energy transmission bridge from exotic photons to Eu^3＋ .

GaN∶Eu^(3+)材料发光特性的调控研究进展

GaN∶Eu^(3+)作为红光发射材料,在GaN基单片集成全色显示器件应用方面具有很大的潜力。目前的研究重点是如何进一步调控和优化GaN∶Eu^(3+)材料的发光特性,促使其迈向实用阶段。本文主要从生长调控,Mg^(2+)、Zn^(2+)、Si^(4+)元素共掺调控,其他稀土元素共掺调控等方面综述了GaN∶Eu^(3+)材料发光特性的研究进展,比较各调控方法的应用潜力,指出GaN∶Eu^(3+)材料今后的研究重点,并对该领域的发展趋势进行了展望。

Enhanced Emission of Eu^(3+) in Boron Ions-Doped Sol-Gel SiO_2 Phosphors

Al-doped and B, Al-codoped silica xerogel was fabricated by sol-gel process. The influence of B ions and annealing temperature on luminescent properties of phosphors were studied by using fluorescence spectrum, X-ray diffraction, DSC, TG/DTG analysis and IR spectrum. The heat treatment has a large effect on the luminescent properties. Under 248 nm excitation, the emission spectrum of samples heated shows characteristic emission peaks of Eu^3＋ ions are, which are due to the transitions of ^5D0→^7FJ（J = 0, 1, 2, 3, 4） of Eu^3＋ , respectively. The transition of ^5D0→^7F1 is split into two peaks.

Spectral Properties and Sensitization of Ce^(3+) and Eu^(2+) Codoped Calcium Zinc Chlorosilicate

The Ce^3+ and Eu^2+ ions codoped calcium zinc chlorosilicate Ca_8Zn(SiO_4)_4Cl_2 phosphors have been synthesized for the first time. The diffuse reflection, excitation and emission spectra of Ca_8Zn(SiO_4)_4Cl_2∶Ce^3+, Eu^2+ have been measured at room temperature. The luminescence sensitizaiton of Eu^2+ by Ce^3+ inCa_8Zn(SiO_4)_4Cl_2∶Ce^3+, Eu^2+ has been expounded under the excitation of ultraviolet light and the efficient nonradiative energy transfer from Ce^3+ to Eu^2+ in this system is confirmed.

Study on Spectra of La_2CaB_(10)O_(19)∶Eu^(3+) in VUV-VIS Range

Excitation and emission spectra of new borate La_2CaB_(10)O_(19) doped Eu^(3+) in VUV-VIS range, high resolution (emission) spectra at room temperature and lifetime of Eu^(3+) were investigated. The emission line at about 616 nm attributed to the (()~5D_0)-(()~7F_2) transition of Eu^(3+) is the most intense emission of Eu^(3+). The broad band at about 244 nm is originated from charge transition band (CTB) of O^(2-)→Eu^(3+). According to the numbers of spectral lines (()~5D_0)-(()~7F_0) and (()~5D_0)-(()~7F_1) in high-resolution spectrum, Eu^(3+) ions occupy two crystallographic sites. The lifetimes of (()~5D_0)-(()~7F_0) transition of Eu^(3+) of two kinds of lattice sites are individually 2.1 and 2.6 ms, and both are exponential decay. In the VUV excitation spectrum, complicated band between 130 and 170 nm consists of host absorption and f-d transition of Eu^(3+).

A novel Eu^(3+)-doped phosphor-in-glass for WLEDs and the effect of borophosphate matrix

Phosphor-in-glass(PiG)is a potential color convertor for high power WLEDs.A novel glass matrix with advanced performance is still a challenge.Recently,Eu^(3+)doped glass matrix has attracted much consideration mainly due to its red compensation.A new borophosphate matrix to realize Eu^(3+)red light was designed in the Na_(2)O-ZnO-P_(2)O_(5)-B_(2)O_(3)-Eu_(2)O_(3)system.Meanwhile,a series of PiGs composed of different concentrations of Y3Al5O12:Ce phosphor and the matrix were also fabricated by re-sintering.The crystallization of Eu^(3+)based phosphate offers a novel red emission quenching apart from normal concentration quenching in the glass system.No direct energy transfer but only little reabso rption occurs between Eu^(3+)and Ce^(3+)ions.The Ce^(3+)concentration effect is obvious on the electroluminescent color.The optimized color rendering index of 79.7,the CIE coordinates near natural white and the range of CCT from 3943 to 6097 K were obtained for the packaged white light emitting diodes(WLEDs)together with the excellent CCT stability higher than about 97.5%and the quadruple thermal conductivity than that of silicon resin.The work implies borophosphate glass based PiGs with fine transparence and energy conversion efficiency are promising for excellent WLEDs,while the LED by using the PiG sample without any yellow phosphor doped is of high color purity and has a potential use as the 465 nm blue source.

White light emission of Eu^(3+)/Ag co-doped Y_2Si_2O_7

The Eu^3＋/Ag co-doped rare earth disilicate Y2Si2O7 microcrystal was synthesized by sol-gel method. Through controlling the thermal treatment process of YzSi2OT：EU3＋/Ag precursor, various phases （amorphous, α, β, γ, δ） were prepared. White light emis- sion was observed under UV light excitation in the samples heavily doped with Ag. The white light was realized by combining the intense red emission of Eu3＋, the green emission attributed to the very small molecule-like, non-plasmonic Ag particles （ML-Ag-particles）, and the blue emission due to Ag ions. Results demonstrated that Eu3＋/Ag co-doped Y2Si207 microcrystal could be potentially applied as white light emission phosphors for UV LED chips.

Enhanced afterglow performance of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors by co-doping Gd^(3+)

In order to effectively improve the afterglow properties of CaAl_(2)O_(4):Eu^(2+),Nd^(3+) phosphors,a series of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)(x=0,0.012,0.024,0.036,0.048,0.060 mol) phosphors were prepared by a high-temperature solid-phase approach.Crystalline composition and microstructure were characterized by XRD,TEM,HRTEM,and XPS,luminescence properties were systematically analyzed by fluorescence spectra,afterglow decay curves and TL glow curve.Results show that all of Ca_(0.982-x)Al_(2)O_(4):0.012 Eu^(2+),0.006 Nd^(3+),xGd^(3+)phosphors belong to monoclinic CaAl_(2)O_(4),without other cystalline phase.The blue emission at 442 nm is observed,which is assigned to the 4f^(6)5 d→4f^(7) transition of Eu^(2+) ions.Doping with appropriate amount of Gd^(3+) ions(x=0.036 mol) significantly improves the afterglow properties of phosphors,but the excessive doping of Gd^(3+) induces the fluorescent quenching.The doping of moderate Gd^(3+) changes the traps states,the trap depth varies from 0.598 to 0.644 eV and the trap concentration is also greatly improved,thus significantly improving afterglow performance.

Growth and Optical Spectra of Tb^(3+)/Eu^(3+) Co-doped Cubic NaYF_4 Single Crystal for White Light Emitting Diode

High quality Tb^3＋/Eu^3＋ co-doped cubic NaYF 4 single crystal in the size of Φ1.0 cm×6.6 cm was grown by a modified Bridgman method using KF as assistant flux for NaF-YF 3 system under the condition of completely closed Pt crucible.A white light emission from the combination of the violet-blue,blue,green,orange,and red lights with chromaticity coordinates of x = 0.3107,y = 0.3274,correlated color temperature of T c = 6637 K,color rendering index of R a = 83,and color quality scale of Q a = 82 could be obtained from 1.51 mol%Tb^3＋ and 1.42 mol%Eu^3＋ co-doped cubic NaYF 4 single crystal when being excited by a 369 nm light.This indicates that Tb^3＋/Eu^3＋）co-doped cubic NaYF 4 single crystal has a potential application in white light emitting diode excited by ultraviolet light.

Multi-site occupancies and luminescence properties of cyan-emitting Ca_(9-x)NaGd_(2/3)(PO_(4))_(7):Eu^(2+)phosphors for white light-emitting diodes

Cyan-emitting Ca_(9)NaGd_(2/3)(PO_(4))_(7):Eu^(2+)phosphors were synthesized via high temperature solid-state route.X-ray powder diffraction(XRD)and scanning electron microscopy(SEM)were used to verify the phase and morphology of the Ca_(9)NaGd_(2/3)(PO_(4))_(7):Eu^(2+)(CNGP:Eu^(2+))phosphors.The as-obtained phosphor exhibits a broad excitation band of 250-420 nm,which is near the ultraviolet region.An intense asymmetric cyan emission at 496 nm corresponds to the 5 d-4 f transition of Eu^(2+).The multiplesite luminescent properties of Eu^(2+)ions in CNGP benefit from versatile structure ofβ-Ca3(PO4)2 compounds.The effective energy transfer distance is 5.46 nm(through the spectral overlap calculation),validating that the resonant energy migration type is via dipole-dipole interaction mechanism.Compared to the initial one at room temperature,the luminescent intensity of CNGP:Eu^(2+)phosphor can maintain 77%as it is heated up to 420 K.A white light-emitting diode(WLED)with excellent luminesce nt properties was successfully fabricated.Moreover,the CIE chromaticity coordinates of fabricated WLED driven by changing current just change slightly.

Preparation,luminescence and photofunctional performances of a hybrid layered gadolinium-europium hydroxide

The design and fabrication of rare earth ions incorporated into the inorganic/organic hybrid materials have attracted growing attention for seeking improved optical properties and photofunctional performances.In this paper,a novel hybrid composite based on the layered rare earth hydroxides was successfully prepared by the ion-exchange and intercalation chemical process.The rare earth elements in the composite contain gadolinium(Gd)and europium(Eu)and the molar ratio of Gd to Eu is kept constant at 1.9:0.1.Organic sodium dodecyl sulfonate and dye coumarin-3-carboxyllc acid are simultaneously incorporated into the layered rare earth hydroxides as supporting agent and light-harvesting antenna,respectively.The resulting hybrid layered rare earth hydroxides exhibit the enlarged interlayer distance with about 2.60 nm,and the chemical composition was confirmed through X-ray diffraction,carbon,hydrogen and nitrogen(CHN)elemental analysis,infrared spectroscopy,and thermogravimetric analysis.The layered solid compound shows the characteristic red emission corresponding to the^(5)D_(0)→^(7)F_(2)transition of Eu^(3+)ion,and the luminescence intensity of the optimized compound is greatly enhanced as compared to its corresponding nitrate and the hybrid composite without the introduction of dye molecule.The hybrid layered rare earth hydroxides can be exfoliated into bright colloidal solution,which show superior recognition capability to Cu^(2+)ion with the distinct luminescence quenching.The large quenching constant(1.4×10^(4)L/mol)and low detection limit(0.35μmol/L)are achieved for Cu^(2+)ion,implying a"turn-off"fluorescent sensor for Cu^(2+)detection.Moreover,a transparent film was prepared based on the colloidal solution and displays the typical red emission in folded shape.The new hybrid compound with enhanced luminescence and excellent photofunctional performances is expected to be applied in the fields of fluorescent sensing and flexible optical devices.