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.

Fabrication and Luminescence Properties of Ca_2Gd_8 (SiO_4 )_6O_2:Er^(3+) Phosphors via Sol-Gel Process

Ca2RE8(SiO4)6O2(RE = Y, Gd, La) is a kind of ternary rare-earth-metal silicate with the oxyapatite structure, which was used as host materials for the luminescence of various rare earth and mercury-like ions. Ca2Gd8(SiO4)6O2: Er3 + phosphors were prepared through the sol-gel process. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectra were used to characterize the resulting phosphors. The results of XRD indicate that the phosphors crystallized completely at 1000℃. SEM study reveals that the average grain size is 400 ~ 1000 nm. In Ca2Gd8 (SiO4)6O2 : Er3+ phosphors, the Er3+ shows its characteristic green emission at 528 nm (2H11/2-4I15/2) and 548 nm (4 S3/2-4 I15/2) upon excitation into 382 nm, with an optimum doping concentration of 5% (mole fraction) of Gd3+ in the host lattices.

Upconversion luminescence of Y_2O_3:Er^(3+), Yb^(3+) nanoparticles prepared by a homogeneous precipitation method

Y2O3： Er^3＋, Yb^3＋ nanoparticles were synthesized by a homogeneous precipitation method without and with different concentrations of EDTA 2Na. Upconversion luminescence spectra of the samples were studied under 980 nm laser excitation. The results of XRD showed that the obtained Y2O3：Er^3＋,Yb^3＋ nanoparticles were of a cubic structure. The average crystallite sizes calculated were in the range of 28-40 nm. Green and red upconversion emission were observed, and attributed to ^2H11/2,^4S3/2→^4I15/2 and ^4F9/2→^4I15/2 transitions of the ion, respectively. The ratio of the intensity of green emission to that of red emission drastically changed with a change in the EDTA 2Na concentration. In the sample synthesized without EDTA, the relative intensity of the green emission was weaker than that of the red emission. The relative intensities of green emission increased with the increased amount of EDTA 2Na used. The possible upconversion luminescence mechanisms were discussed.

Synthesis and upconversion luminescence properties of NaYF_4:Yb^(3+)/Er^(3+) microspheres

Cubic NaYF4：Yb^3＋（20%）/Er^3＋（1%） microspheres were synthesized by EDTA-assisted hydrothermal method. Under 980 nm excitation, ultraviolet （^4G11/2→^4I15/2）, violet （^2H9/2→^4I15/2）, green （^4F7/2→^4I15/2, 2H11/2→^4I15/2, and ^4S3/2→^4I15/2）, and red （^4F9/2→^4I15/2） upconversion fluorescence were observed. The number of laser photons absorbed in one upconversion excitation process, n, was determined to be 3.89, 1.61, 2.55, and 1.09 for the ultraviolet, violet, green, and red emissions, respectively. Obviously, n=3.89 indicated that a four-photon process was involved in populating the ^4G11/2 state, and n=2.55 indicated that a three-photon process was involved in populating the ^4F7/2/^2H11/2/^4S3/2 levels. For the violet and red emissions, the population of the states ^2H9/2 and ^4F9/2 separately came from three-photon and two-photon processes. The decrease of n was well explained by the mechanism of competition between linear decay and upconversion processes for the depletion of the intermediate excited states.

Research of Three-Dimensional Fluorescence Spectra of RE^(3+)(RE=Eu,Tb) and Na_2WO_4 Co-doped Silica Luminescence Materials

In the preparation of this precursor tetraethlortho silicate (TEOS), sodium tungstate, ethyl alcohol, HCl and RECl3(RE=Eu,Tb) were mixed and then heated at 800 ℃ for 2 h, leading to a luminescent compound. The structure of the materials was characterized by TG-DTA and IR analysis, and the results indicate that the materials were in SiO2 network structure. Three-dimensional fluorescence spectra was used to characterize the luminescent properties of the materials. The luminescence property of doped and un-doped Eu3+or Tb3+ and Na2WO4 in silica materials were prepared and measured. The results show that good energy transfer from WO2-4 to Eu3+ ion, sensitized the luminescence intensity of Eu3+ remarkably. Tb3+ ion incorporated silica materials expressed the inverse energy transition from Tb3+ to WO2-4, however, we got the materials with homogeneous green blue fluorescent light. Finally, the energy transfer of WO2-4 and Eu3+, WO2-4 and Tb3+ were explained by energy levels diagram.

Preparation and Luminescence of Er^(3+) Doped Oxyfluoride Glass Ceramics Containing LaF_3 Nanocrystals

Er^3＋ doped transparent oxyfluoride glass ceramics version and near infrared luminescence behavior of Er^3＋ in containing LaF3 nanocrystals were prepared and the up-conglasses heat-treating time and temperature, the size （varied from 0 to 19 and glass ceramics were investigated. With increasing nm） and crystallinity （varied from 0 to 47%） of LaF3 nanocrystals in the glass ceramics are increased. The up-conversion luminescence intensity of Er^3＋ ions in the glass ceramics is much stronger than that in the glasses The near infrared emission of Er^3＋ ions in and increased significantly with increasing heat-treating time and temperature the glass ceramics is found to be similar to that in the glasses.

UV and visible upconversion luminescence in Er^3＋：YAG under red laser excitation

This paper reports that the ultraviolet and visible upconversion luminescence from the ^4S3/2, ^2G9/2 and ^2P3/2 levels have been observed in Er^3＋：YAG following 647.2 nm excitation of the ^4F9/2 multiple. Upconversion luminescence intensity dependence on pump power was recorded. The measured decay profiles were theoretically fitted by kinetics theory and the basically good agreements were achieved. The results indicate that some energy transfer processes proposed to explain the observed upconversion phenomena are reasonable.

Synthesis and Upconversion Luminescence of LaF_3:Yb^(3+),Er^(3+)/SiO_2 Core/Shell Microcrystals

LaF3：Yb^3＋ , Er^＋ microcrystals were synthesized by a hydrothermal method, and then, the LaF3： Yb^3＋ , Er^＋ microcrystals were coated with silica. Phase identification of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 was performed via XRD. The TEM image showed that the size of LaF3： Yb^3＋ , Er^＋ was 150 nm and LaF3： Yb^3＋ , Er^＋/SiO2 presented clearly a core/shell structure with 20 nm shell thickness. The upconversion spectra of LaF3： Yb^3＋ , Er^＋ and LaF3： Yb^3＋ , Er^＋/SiO2 in solid state and in ethanol were studied with a 980 nm diode laser as the excitation source. The upconversion spectra showed that the silica shell had little effect on the properties of fluorescence of the LaF3：Yb^3＋ , Er^＋ microcrystals. At the same time, the green luminescence photo of LaF3： Yb3＋, Er3＋/SiO2 in the PBS buffer was obtained, which indicated that the LaF3： Yb^3＋ , Er^＋/SiO2 could be used in biological applications.

Shape controllable synthesis and enhanced upconversion photoluminescence ofβ-NaGdF4:Yb^3+,Er^3+nanocrystals by introducing Mg(^2+)

Different concentrations of Mg^（2＋） -doped hexagonal phase NaGdF_4：Yb^（3＋）, Er^（3＋）nanocrystals（NCs） were synthesized by a modified solvothermal method. Successful codoping of Mg^（2＋）ions in upconversion nanoparticles（UCNPs） was supported by XRD, SEM, EDS, and PL analyses. The effects of Mg^（2＋）doping on the morphology and the intensity of the upconversion（UC） emission were discussed in detail. It turned out that with the concentration of Mg^（2＋）increasing, the morphology of the nanoparticles turn to change gradually and the UC emission was increasing gradually as well. Notably the UC fluorescence intensities of Er^（3＋）were gradually improved owing to the codoped Mg^（2＋）and then achieved a maximum level as the concentration of Mg^（2＋）ions was 60 mol% from the amendment of the crystal structure of β-NaGdF_4：Yb^（3＋）,Er^（3＋）nanoparticles. Moreover, the UC luminescence properties of the rare-earth（Yb3＋, Er^（3＋）） ions codoped NaGdF_4 nanocrystals were investigated in detail under 980-nm excitation.

Preparation and Upconversion Luminescence of Y_3Al_5O_(12):Yb^(3+),Er^(3+)Transparent Ceramics

YAG： 1% （atom fraction） Yb^3＋ , 0.5% （atom fraction） Er3＋ transparent ceramics were fabricated by the solid state reaction method using high-purity Y2O3, Al2O3, Yb2O3, and Er2O3 powders as starting materials. The mixed powder compact was sintered at 1760 ℃ for 6 h in vacuum and annealed at 1500 ℃ for 10 h in an air atmosphere. The ceramics consisted of about 10μm grains and exhibited a pore-free structure. The optical transmittance of the ceramics at 1064 nm was nearly 80%. Upconversion emissions were investigated on the ceramics pumped by a 980 nm continuous wave diode laser, and strong green emission centered at 523 and 559 nm and red emission centered at 669 nm were observed, which originated from the radiative transitions of ^2H11/2→^4I15/2, ^4S3/2→^4I15/2, and ^4F9/2→^4I15/2 of Er^3＋ ions, respectively.

Up-conversion luminescence properties and energy transfer of Er^(3+)/Yb^(3+)co-doped oxyfluoride glass ceramic containing CaF_2 nano-crystals

The Er^3＋/yb^3＋ co-doped transparent oxyfluoride glass-ceramics containing CaF2 nano-crystals were successfully prepared. After heat treatments, transmission electron microscopy （TEM） images showed that CaF2 nano-crystals of 20-30 nm in diameter precipitated uniformly in the glass matrix. luminescence of Er^3＋ at 540 nm and 658 nm was observed in Comparing with the host glass, high efficiency upconversion the glass ceramics under the excitation of 980 nm. Moreover, the size of the precipitated nano-crystals can be controlled by heat-treatment temperature and time. With the increase of the nano-crystal size, the intensity of the red emission increased more rapidly than that of the green emission. The energy transfer process of Er^3＋ and Yb^3＋ was convinced and the possible mechanism of Er^3＋ up-conversion was discussed.

Upconversion Luminescence Properties and Mechanism of Er^(3+) Doped Ba_(0.65)Sr_(0.35)TiO_3 Ferroelectric Oxide Nanocrystals

Ba0.65Sr0.35TiO3（BST） nanocrystals doped with different concentrations of Er^3＋ ion were fabricated using sol-gel method. The structure and morphology of these BST nanocrystals were studied using X-ray diffraction（XRD）, field emission scanning electron microscopy（FESEM） and transmission electron microscopy（TEM）. The X-ray diffraction patterns of all the nanocrystals prepared in the study correspond to polycrystalline perovskite BST structure. The blue and green upconversion luminescence properties of Er^3＋ doped BST nanocrystals were investigated under excitation by a 785-nm laser. The upconversion emission bands centered at 407, 523, and 547 nm can be attributed to ^2H9/2, ^4I15/2, ^2H11/2, ^4I15/2, and ^4S3/2, 4I15/2 transitions of Er^3＋ ion, respectively. The upconversion mechanism was studied in detail, based on the laser power dependence of the upconverted emissions. In addition, we examined the dependence of the intensity of green upconverted luminescence on the doping concentration of Er^3＋ ions, and discussed the mechanism underlying the process.

Frequency Up-conversion Luminescence Properties and Mechanism of Tm^(3+) /Er^(3+)/Yb^(3+) Co-doped Oxyfluorogermanate Glasses

Oxyfluoride glasses were developed with composition 60GeO 2 ·10AlF 3 ·25BaF 2 ·（1.95-x）GdF 3 · 3YbF 3 ·0.05TmF 3 ·xErF 3 （x=0.02,0.05,0.08,0.11,0.14,0.17）in mole percent.Intense blue（476 nm）,green（524 and 546 nm）and red（658 nm）emissions which identified from the 1G 4 →3H 6 transition of Tm3＋and the（2H 11/2 ,4S 3/2 ）→4I 15/2 ,4F 9/2 →4I 15/2 transitions of Er3＋,respectively,were simultaneously observed under 980 nm excitation at room temperature.The results show that multicolor luminescence including white light can be adjustably tuned by changing doping concentrations of Er3＋ion or the excitation power.In addition,the energy transfer processes among Tm3＋,Er3＋and Yb3＋ions,and up-conversion mechanisms are discussed.

Shape-Controlled Synthesis and Upconversion Luminescence of Y2O3: Yb, Er Microstructures

The Y2O3: Yb3+ , Er3 + microstructures were fabricated by a hydrothermal method without surfactants.The microstructures structure was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM,KYKY 1000B).The up-conversion luminescence spectra were studied under 978 nm laser diode excitation.In Yb3 + and Er3 + codoped Y2 O3 microcrystals, the relative intensity of green emission became stronger as the morphology of sample changed from wires to films.

Laser-diode excited intense upconversion luminescence of Er^3＋ in bismuth-lead-germanate glasses

We have investigated infrared-to-visible upconversion luminescence of Er^3＋ in bismuth-lead-germanate glasses. The UV cutoff wavelength is shortened while its lifetime is increased almost linearly, with PbF2 substituting for PbO in the bismuth-lead germanate glasses. Three emissions centred at around 529, 545 and 657 nm are clearly observed, which are identified as originating from the ^2H11/2→^4 I15/2,^4S3/2→^4 I15/2 and ^4 F9/2 →^4 I15/2 transitions, respectively. It is noted that all the upconversion emission intensities increase with PbF2 concentration increasing. The ratio between the intensities of red and green emissions increases with the increasing of PbF2 content. Energy transfer processes and nonradiative phonon-assisted decays account for the populations of the ^2 H11/2,^4 S3/2 and ^4F 9/2 levels. The quadratic dependence of fluorescence on excitation laser power confirms a two-photon process to contribute to the upconversion emissions.

Preparation of NaYF_4:Er^(3+)/TiO_2 composite and up-conversion luminescence properties under visible light excitation

The up-conversion luminescence composite NaYF4：Er3＋/TiO2 is prepared using the sol-gel method. The specimen has good crystallinity and two shapes, i.e., viereck and round, while the sizes of viereck and round particles are both micron-sized. The TiO2 has an anatase structure, while the NaYF4 has a hexagonal phase, which can be hardly obtained through the common sol-gel method. Due to the big particle size and the high crystallinity of pure NaYF4： Er3＋, the composite has a small specific surface area that is less than Degussa P25 TiO2. The NaYF4：Er3＋/TiO2 composite shows several emission peaks at 211, 237, and 251 nm under the excitation of 388 nm, at 395 nm and 411 nm under the excitation of 500 nm, and at 467, 481,492, and 508 nm under the excitation of 570 nm.

Upconversion Luminescence of Er^(3+), Tm^(3+) and Yb^(3+)Co-doped Gd_3Ga_5O_(12) Nanocrystals

A series of Er3＋, Tm3＋ and Yb3＋ doped Gd3Ga5O12 nanocrystals were prepared by a combustion method. The X-ray diffraction （XRD）, field emission scanning electron microscope （FESEM） and upconversion （UC） emission spectra were used to characterize the samples. The results of XRD indicate that Gd3Ga5O12：Er3＋, Tm3＋, Yb3＋ nanocrystals with cubic phase can be obtained. Under the excitation of a 980 nm laser, the different rare earth ions doped Gd3Ga5O12 nanoerystals show upconversion luminescence involving the green emission attributed to the ^2H11/2→^4I15/2, 4^S3/2→^4I15/2 transitions of Er3＋ ions, respectively, the red emissions assigned to the ^4F9/2→^4I15/2 transitions of Er3＋ ions and the ^1G4→^3F4 as well as 3F2,3→^3H6 transitions of Tm3＋ ions, respectively, the blue emission attributed to ^1G4→^3H6 transitions of Tm3＋ ions, and the near-infrared assigned to the ^3H4→^3H6 transitions of Tm3＋ ions. The CIE coordinates for the samples are calculated. The dependence of their upconversion luminescence properties on Yb3＋ ion concentration is investieated.

Preparation and upconversion luminescence properties of LaF_3:Yb^(3 +),Er^(3 +) /SiO_2 nanocomposites with core /shell structure

LaF^3＋ Yb^3＋ , Er^3＋ nanoparticles were successfully synthesized using solvothermal treatment, and LaF^3＋ Yb^3＋ , Er^3＋/SiO2 core/shell nanoparticles were also prepared with reverse microemulsion technique. The crystal structure, morphology and photoluminescence properties of as-prepared core/shell nanoparticles were in- vestigated by X-ray diffraction, transmission electron microscopy and fluorescence spectrophotometer. The re- sults showed thatLaF^3＋ Yb^3＋ , Er^3＋ nanoparticles are of hexagonal structure and SiO2 shell is amorphous. The size ofLaF^3＋ Yb^3＋ , Er^3＋. nanoparticles is 13 nm and the LaF^3＋ Yb^3＋ , Er^3＋/SiO2 nanoparticles present clearly a core/shell structure with 12 nm shell thickness. The solubility of LaF^3＋ Yb^3＋ , Er^3＋ nanocrystals in water and the biocompatibility are both improved by the SiO2 shell. The upconversion luminescence spectra suggested that the SiO~ shell has small effect on the upconversion luminescence properties of the LaF^3＋ Yb^3＋ , Er^3＋ nanocrys- tals. The core/shell structure LaF^3＋ Yb^3＋ , Er^3＋ /SiO2. nanopartlcles are expected to be used in biological appli- cations.

Improvement of Luminescent Properties of PbWO_4 by Doping with Gd^(3+) Ions

The luminescent properties of PbWO 4∶Gd 3+ were studied. The luminescence of Gd 3+ in PbWO 4∶Gd 3+ was quenched. It is possible that the excitation states of Gd 3+ locate in the conduction band of PbWO 4 crystal. The luminescent intensity of the green and the blue band of PbWO 4 emission increases by doping with about 0 005% and 0 01% (molar fraction) Gd 3+ respectively. Mechanism of this enhancement of PbWO 4∶Gd 3+ luminescence is probably due to energy transfer from Gd 3+ to PbWO 4 host in the crystal. The PbWO 4 doped with low concentration of Gd (about 0 005%～0 01%) is a good scintillating material.

Fabrication and photoluminescence of Er-doped ZnO thin films on SiO_2/Si substrate by pulsed laser deposition

Er doped ZnO thin films were grown on Si substrates using SiO2 buffer layer by pulsed laser deposition (PLD) method. The obtained films crystallize well and show high c-axis orientation. The Er content was evidently detected by the energy dispersive X-ray spectroscopy (EDS). Upon annealing in O2 ambience at different temperatures, the films show different photoluminescence properties at 1.54 μm. The samples annealed at 700 and 850 ℃ show intense photoluminescence peaks which enhance with the annealing temperature, while no obvious luminescence peaks are observed for the as-grown samples or annealed at 500 ℃. The possible mechanism was discussed.