YAG Host Research Articles

A novel solid-state synthesis of long afterglow, Si–N co-doped, Y3Al5O12:Ce3+ phosphor

Si–N co-doped Y3Al5O12:Ce3+ (YAG:Ce) phosphor was synthesized via a novel solid-state reaction method using CeSiO2N to simultaneously incorporate Si–N and Ce3+. The achieved phosphor exhibits increased red light component and better thermal quenching property. Additionally, an evident long afterglow luminescence was detected for the first time. The analysis of the experimental results (X-ray diffraction, photoluminescence, X-ray absorption near edge spectroscopy, infrared spectroscopy, and thermoluminescence) suggests that the Si–N was homogeneously incorporated into YAG host lattice and most of the Ce3+ ions were directly coordinated with nitrogen. The deeper trap depth and greater number of oxygen vacancies around Ce3+ are responsible for the significantly enhanced long afterglow in Si–N co-doped YAG:Ce phosphor.

Synthesis, characterization and optical properties of Y3Al5O12:Ce phosphor by mixed fuel combustion synthesis

YAG:Ce phosphors have been synthesized by single step combustion synthesis employing glycine-urea fuels at 500C. Crystal structures, luminescent properties of the phosphors are analyzed. XRD study of polycrystalline powder shows the formation of YAG phase at low temperature and crystallite size found in the range of 28 nm size. Photoluminescence emission spectra of YAG:Ce phosphor exhibited broad greenish yellow emission from Ce3+. The emission spectra of phosphors show gradual shift towards longer wavelength with the increase of doping concentration of Ce3+ however results in significant decrease in the emission intensity. The critical distance of the energy transfer has been calculated by the concentration-quenching method. The energy transfer mechanism between Ce3+ ions in YAG host has been studied in detail. The concentration-quenching mechanism can be explained by the electric dipole–dipole interaction of the Ce3+ ions. Commission Internationale de l'Eclairage (CIE) co-ordinate of phosphor studied for and found suitable for wLEDs.

Photoluminescence enhancement of YAG:Ce nanophosphors with SiO2 additions

Co-precipitated Y3Al5O12:Ce nanophosphors with enhanced photoluminescence (PL) intensity were synthesized by introducing SiO2 in the precursor. The role of SiO2 on morphologies, PL enhancement and valence state of Ce was investigated by varying the amounts of SiO2 from 0 to 1.0 wt%. The SiO2 addition inhibited the crystal growth owing to the appearance of second phase. However, the PL intensity of YAG:Ce was largely improved with SiO2 addition. The reason for the PL enhancement was that the incorporation of Si4+ into the YAG host suppressed the further oxidation of Ce3+ to Ce4+ owing to charge compensation.

Nanomaterial Host Bands Effect on the Photoluminescence Properties of Ce‐Doped YAG Nanophosphor Synthesized by Sol‐Gel Method

Cerium trivalent (Ce3+) doped YAG nano‐sized phosphors have been successfully synthesized by sol‐gel method using different annealing temperatures. The samples have been characterized by X‐ray diffraction (XRD), thermogravimetry (TG), differential scanning calorimetry (DSC) analysis, Fourier transform infrared (FTIR) spectroscopy, and steady photoluminescence (PL) spectroscopy. X‐ray diffraction analysis indicates that the pure cubic phase YAG was formed and strongly depends on the cerium content and the annealing temperature. It was found that the grain size ranges from 30 to 58 nm depending on the calcination temperature. The YAG: Ce nanophosphors showed intense, green‐yellow emission, corresponding to Ce3+ 5d1→2F5/2, 2F7/2 transitions and its photoluminescence excitation spectrum contains the two Ce3+ 4f1→5d1, 5d2 bands. The crystal filed splitting energy levels positions 5d1 and 5d2 and the emission transitions blue shift with annealing temperatures have been discussed. It was found that the Ce3+ 4f1 ground state position relative to valence band maximum of YAG host nanomaterial decreases with increasing the temperature.

Luminescent properties and energy transfer processes in YAG:Er single crystalline films

The paper is dedicated to studying the optical properties of YAG:Er single crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and photoluminescence spectra were measured for the YAG:Er SCFs with different doping levels of Er3+ from 0.735 to 6.6at%. The luminescence spectra and luminescence excitation spectra under synchrotron radiation excitation in the fundamental absorption range of the YAG and in the intrinsic f–d absorption bands of Er3+ ions reveal the peculiarities of energy transfer from the YAG host to the Er3+ ions.

Effect of Ga3+ Doping on the Photoluminescence Properties of Y3Al5-xGaxO12:Bi3+ Phosphor

The structural and luminescence characteristics of a sol-gel combustion synthesized Y3Al5-xGaxO12:Bi3+ phosphor with different concentration of Ga3+were investigated. The Rietveld refinement analysis and luminescence studies indicated that increasing the concentration of the Ga ions changed the bond lengths and lattice parameters of the dodecahedron bonds and as a result the Bi3+ experienced a different anionic environment in the YAG host. A systematic shift of the photoluminescence excitation and emission spectra to higher wavelengths was observed with an increase of the Ga3+ concentration. The shift is attributed to the distortion of the host lattice as observed from the changing parameter and the covalency of the host with an increase of the Ga3+ concentration.

Comparison of Ce3+/Yb3+ with Er3+/Yb3+ down-conversion pairs in YAG host for improving the efficiency of the crystalline silicon solar cells

Re3+, Yb3+ co-doped (Re0.005YbxY(0.995-x))3Al5O12 [Re = Ce, Er, x = 0, 0.02, 0.05, 0.1, and 0.2] transparent ceramics are synthesized by the solid state reaction and vacuum sintering as the down-conversion (DC) materials. The photoluminescence excitation and the photoluminescence spectra demonstrate the near-infrared quantum cutting (QC) and the energy transfer (ET) from Re3+ to Yb3+ in both of these series of samples. The comparison of the near-infrared QC spectra of the two series of samples shows that the Ce3+, Yb3+ co-doped Y3Al5O12 transparent ceramic samples have much higher intensity of the emission spectra in the near-infrared region, and higher ET efficiency than the Er3+, Yb3+ co-doped ones. So, the Ce3+, Yb3+ DC ion pair is a better choice to improve the efficiency of the crystalline silicon-based solar cells.

Parasitic Light Absorption Processes in Transparent Polycrystalline MgAl2O4 and YAG

Parasitic radiation absorption by impurities located in transparent polycrystalline ceramic hosts may significantly impair their functioning. At least two classes of impurity which can act as parasitic absorbers were encountered: transition or rare‐earth metal cations and neutral species (molecules or atoms) trapped in lattice void spaces. The most ubiquitous parasitic absorbers, able to affect transmission in the visible domain, have been identified for the case of MgAl2O4‐spinel and Y3Al5O12‐garnet hosts; their spectral effect was described and explained. In the case of spinel, S8 type molecules and carbon atom clusters are the most damaging impurities, with Ce3+ and Y2+ also of significance for YAG host. Oxygen vacancy formation assists some of the redox processes which generate uncontrolled absorption. For instance, the Ti4+ reduction to Ti3+ is facilitated by such a process.

Luminescence properties and energy transfer processes in YAG:Yb,Er single crystalline films

The paper is dedicated to the study of the optical properties of YAG:Yb,Er single-crystalline films (SCF) grown by liquid phase epitaxy. The absorption, cathodoluminescence and time-resolved photoluminescence spectra and photoluminescence decay curves were measured for the SCFs with different doping levels of Er3+ (from 0.6 to 4.2 at.%) and Yb3+ (from 0.1 to 0.6 at.%). The spectra, excited by synchrotron radiation in the fundamental absorption range of the YAG and in the intraionic absorption bands of both dopants, reveal energy transfer from the YAG host to the Er3+ and Yb3+ ions and between these ions.

Tunable luminescence Y_3Al_5O_12:006Ce^3+, xMn^2+ phosphors with different charge compensators for warm white light emitting diodes

Y₃Al₅O₁₂:0.06Ce³⁺, xMn²⁺ (YAG:0.06Ce,xMn) phosphors have been synthesized and the effect of different charge compensators on the color adjustment has been investigated for the first time. The luminescence properties of Mn2+ singly doped and co-doped with Ce3+ into YAG host have been discussed. It is observed that in singly doped sample, Mn2+ ions not only occupy two kinds of Al3+ sites to generate a yellow and a deep red emission bands, but also occupy Y3+ sites to obtain a green emission band in YAG host. Considering Mn2+ substitution for Al3+, quadrivalence ions including Zr4+, Ge4+ and Si4+ ions are introduced to balance the charge difference. The results show that Si4+ as charge compensator exhibits the best tunable effect on controlling the Mn2+ emissions in YAG:0.06Ce, xMn. In Si4+-Mn2+ co-doped samples, the emission color can be tuned from greenish-yellow to red with increasing the content of Mn2+. The Commission International de L’Eclairage (CIE) chromaticity coordinates are also investigated.

Comparative study of the luminescence of Y3Al5O12 nanoceramics and single crystals under excitation by synchrotron radiation

Comparative investigation of the luminescent properties of Y3Al5O12 (YAG) nanoceramics with the properties of single crystals counterpart is performed under excitation by synchrotron radiation in the exciton range of YAG host. Analysis of the luminescent properties of such different crystalline forms of YAG allows us to conclude that the behavior of YAG nanoceramics is close to the properties of single crystal analogue with large content of YAl antisite defects (ADs). We also have found that the relative intensity of F+–AD coupled centers is significantly higher in YAG nanoceramics than that for single crystal counterpart. This presupposes the strong coupling of the antisite defects and oxygen vacancy-related centers in YAG nanoceramics, mainly at the boundaries of grains.

Waveguiding properties in Yb:YAG crystals implanted with protons and carbon ions

We report the fabrication and analysis of optical waveguides in Yb:YAG crystals using either proton or carbon ion implantation. Planar waveguides were obtained by implanting the whole surface of the crystals. Channel waveguides were defined using an electroformed mask with apertures of 10, 15, and 20 micrometers in width. The waveguiding properties of the structures were analyzed, showing good light confinement based on the transversal mode distribution and optical transmission measurements. The spectroscopic properties of the Yb ions in the YAG host are preserved after the implantation process, which demonstrates the potential of this technique for tailoring microcomponents for integrated optics applications. In particular, the Yb:YAG waveguides have the potential to operate as miniature lasers.

Peculiarities of luminescent and scintillation properties of YAG:Ce phosphor prepared in different crystalline forms

In this work, we have performed the comparative analysis of the luminescent and scintillation properties of Y3Al5O12:Ce (YAG:Ce) single crystals (SC), single crystalline films (SCF) and transparent optical ceramics (OС) using the traditional spectral methods as well as the luminescence spectroscopy under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. We have shown that the properties of YAG:Ce OC are rather closer to the properties of SCF counterpart where YAl antisite defects are completely absent than to the properties of SC of this garnet with large concentration of YAl antisite defects. At the same time, the luminescence spectra of YAG:Ce OC and SC show the emission bands in the 200–450nm range related to YAl antisite defects and charged oxygen vacancies (F+ and F-centers). YAG:Ce ОС also possesses significantly higher thermoluminescence in the range above room temperature and large contribution of slow components in the Ce3+ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet. The mentioned properties of YAG:Ce OC are caused by the participation of antisite defects and charged oxygen vacancies located in OC mainly on the boundaries of grains, as trapping centers in the energy transfer processes from the host to the Ce3+ ions.

Incorporation of Si–O induced valence state variation of cerium ion and phase evolution in YAG:Ce phosphors for white light emitting diodes

The role of Si4+ in the valence state of Ce and phase control in YAG:Ce phosphors was investigated upon incorporation of Si–O in the form of SiO2. By varying the amount of SiO2 addition, the valence state of tetravalent and trivalent Ce ions was identified distinctly by X-ray photoelectron spectroscopy and the phase purity of YAG host phase was examined by X-ray diffraction patterns. The self-reduction phenomena from Ce4+ to Ce3+ in YAG:Ce samples was observed to be featured in a typical 5d → 4f yellow-green transition of Ce3+ ion upon firing in air, driven by charge compensation for imbalance substitution of Ce4+ for Y3+. The addition of SiO2 promotes further reduction of Ce4+ to Ce3+ in an amount up to 7.0 wt%, owing to spontaneous charge compensation, and suppresses the formation of YAP (yttrium aluminate perovskite, YAlO3) and YAM (yttrium aluminate monoclinic, Y4Al2O9). The results reveal the role of SiO2 addition in a proper amount to be able to achieve desired luminous center of Ce3+ and phase-pure YAG for a series of YAG hosted luminescence materials such as blue-excitable YAG phosphor or laser-pumped YAG-based transparent ceramics or glass ceramics for lighting and display purposes.

Microstructure and Photoluminescence Characterizations of Y3Al5O12:Ce Phosphor Ceramics Sintered with Silica

The effects of silica additions (0.5–5 wt%) and sintering temperatures (980°C–1400°C) on the microstructure and photoluminescence (PL) of Ce‐doped Y3Al5O12 (YAG:Ce) phosphor ceramics were investigated in this study. Fourier transform infrared (FTIR) measurements showed the disappearance of silica (1 wt%) at 1200°C, indicating the incorporation of Si into YAG host and agreeing with the nuclear magnetic resonance (NMR) results. Microstructures of YAG:Ce ceramics with various silica additions observed using scanning electron microscope (SEM) and transmission electron microscope (TEM) revealed an obvious increasing densification and grain growth for the samples of >2.5 wt% silica at 1400°C. PL analysis demonstrated a higher intensity with increasing the sintering temperatures and the amount of silica addition. Two reasons were supposed to induce this PL enhancement of silica‐treated YAG:Ce ceramics. First, Si will replace tetrahedral Al sites and induce a homogeneous diffusion as well as distribution of Ce dopant in the YAG host due to a smaller ionic radius of Si (0.026 nm) than that of Al (0.039 nm). Secondly, a liquid phase sintering will occur with the presence of silica in YAG:Ce, resulting in the densification of ceramics and an easier migration of Ce activators to inhibit the concentration quenching effect.

Long-lasting phosphorescence study on Y 3Al 5O 12 doped with different concentrations of Ce 3+

Long-lasting phosphorescence (LLP) was observed in Ce-doped Y 3Al 5O 12 phosphors synthesized in reducing atmosphere. The characteristic emission of the 2D- 2F 5/2 and 2D- 2F 7/2 transition of Ce 3+ in photoluminescence (PL) and LLP spectra was studied. It was interesting that the ratio between the peak areas of 2D- 2F 5/2 and 2D- 2F 7/2 transitions in the PL spectrum was different from the ratio of that in LLP emission spectrum. And the ratios had different change regularities with increased Ce 3+ concentration. The possible reason was attributed to the defect in the YAG host, which was affected by increasing the Ce 3+ concentration. There were indications that the defect in the Ce 3+-doped YAG samples was strongly associated with oxygen vacancy. And the defect levels were studied through thermoluminescence (TL) experiment. The results showed that the trap depth was between 0.6 and 0.65 eV, and the kinetic order of the LLP was 2.

Extraction of crystal-field parameters for lanthanide ions from quantum-chemicalcalculations

A simple method for constructing effective Hamiltonians for the4fN and4fN − 15d energy levels of lanthanide ions in crystals from quantum-chemical calculations is presented.The method is demonstrated by deriving crystal-field and spin–orbit parameters forCe3 + ionsdoped in LiYF4, Cs2NaYCl6,CaF2,KY3F10 and YAG host crystals from quantum-chemical calculations based on the DV-Xα method. Good agreement between calculated and fitted values of the crystal-fieldparameters is obtained. The method can be used to calculate parameters even forlow-symmetry sites where there are more parameters than energy levels.

Facile Synthesis of Ce3+, Eu3+ Co-Doped YAG Nanophosphor for White Light-Emitting Diodes

Luminescent Ce3+, Eu3+ co-doped yttrium aluminum garnet (Y3Al5O12, YAG) nanophosphors were successfully synthesized by a facile hydrothermal-assistant combustion method without a reducing atmosphere. The photoluminescence (PL) spectrum of the as-prepared YAG:Ce3+, Eu3+ nanophosphors consisted of a typical broad yellow emission band attributed to the characteristic emission of Ce3+ and several sharp emission bands in red spectral region attributed to the characteristic emission of Eu3+ due to the successful co-doping of Eu3+ into YAG host lattice, and the intensities of these sharp red emission bands could be adjusted by varying the Eu3+ doping concentration. The energy transfer from Ce3+ to Eu3+ inside YAG was also investigated, and the results showed that both Ce3+ and Eu3+ could be efficiently excited by 465 nm blue light, which indicated the red emission of YAG:Ce3+, Eu3+ under 465 nm blue light excitation was not merely enhanced at the cost of emission intensity of Ce3+. Moreover, YAG: Ce3+, Eu3+ nanophosphors were combined with blue light-emitting diode (LED) chip to fabricate white LED, and the resulting white LED showed good performance with a luminous efficiency of 70.4 lm/W, Ra of 82, and Tc of 4964 K at 100 mA.

Luminescence properties of Y3Al5O12:Ce nanoceramics

Abstract Comparative analysis of the luminescent properties of Y 3 Al 5 O 12 :Ce (YAG:Ce) transparent optical ceramics (OС) with those of single crystal (SC) and single crystalline film (SCF) analogues has been performed under excitation by pulsed synchrotron radiation in the fundamental absorption range of YAG host. It has been shown that the properties of YAG:Ce OC are closer to the properties of the SCF counterpart, where Y Al antisite defects are completely absent, rather than to the properties of SC of this garnet with large concentration of Y Al antisite defects. At the same time, the luminescence spectra of YAG:Ce OC show weak emission bands in the 200–470 nm range related to Y Al antisite defects and charged oxygen vacancies (F + and F centers). YAG:Ce ОС also possesses significantly larger contribution of slow components in the Ce 3+ luminescence decay under high-energy excitation in comparison with SC and SCF of this garnet due to the involvement of antisite defects, charged oxygen vacancies as well as boundaries of grains in the energy transfer processes from the host to the Ce 3+ ions.

Time-resolved luminescent spectroscopy of YAG:Ce single crystal and single crystalline films

Abstract The peculiarities of the luminescence and energy transfer from YAG host to the emission centers formed by the Y Al antisite defects and Ce 3+ ions have been studied in YAG:Ce single crystals, grown from the melt by modified Bridgman method in Ar and CO 2 + H 2 atmospheres, and YAG:Ce single crystalline film, grown by liquid phase epitaxy method, using the comparative time-resolved luminescent spectroscopy under excitation by synchrotron radiation in the range of fundamental adsorption of this garnet.