Ions In YAG Research Articles

Highly transparent Ce:Nd:YAG ceramic with good light conversion capacity for solar-pumped solid-state lasers

Developing a high quality ceramic laser gain medium for solar directly pumped solid state lasers is essential, and yet the light conversion efficiency of the gain media for solar pumping remains a challenge. In this study, Ce and Nd ions, co-doped YAG transparent ceramics with theoretical transmittance and stable Ce3+ valent state were developed, and revealed that the absorbed visible light and light conversion efficiency in Ce,Nd:YAG ceramics were 3.98 times and 1.34 times higher than those in widely reported Cr,Nd:YAG ceramics, respectively. A concentration matching principle between Ce3+ and Nd3+ ions in YAG was established, and a higher Nd3+ ion doping concentration with a relatively low Ce3+ concentration was favorable to improve both the light conversion efficiency and emission intensity at 1064 nm of Ce,Nd:YAG ceramics. Energy transfer efficiency from Ce3+ to Nd3+ of the 0.3 at.%Ce,1.5at.%Nd:YAG ceramic reached as high as 61.71% at room temperature. Surprisingly, it was further promoted to 64.31% at a higher temperature of 473 K. More excited electrons at the upper energy level of Ce3+ ion under the high temperature accounted for this novel phenomenon. This study proposes a new design strategy of gain materials for solar directly pumped solid state lasers.

Synthesis and luminescent properties of Eu3+, Eu3+/Bi3+ and Gd3+ codoped YAG:Ce3+ phosphors and their potential applications in warm white light-emitting diodes

A series of YAG:Ce3+/Eu3+, YAG:Ce3+/Eu3+/Bi3+ and YAG:Ce3+/Gd3+ phosphors were synthesized by a co-precipitation method. The results suggest that all of phosphors have the cubic phase and nearly spherical morphology. However, the red emission can be produced by codoping Eu3+ and Eu3+/Bi3+ ions in YAG:Ce3+, and the codoped Gd3+ ions can induce the red-shift of Ce3+ emission. These results suggest that the Eu3+, Eu3+/Bi3+ and Gd3+ ions can be used to decrease the correlated color temperature and increase the color-rendering index of white light-emitting diodes based on InGaN blue chip and YAG:Ce3+ phosphors.

Spectral and laser properties of Nd:YSAG single crystal

In order to solve the problem of low segregation coefficient of Nd3+ ions in YAG crystal, Sc3+ ions are used to replace some Al3+ ions in YAG, so that the YAG cell becomes bigger, thereby the segregation coefficient of Nd3+ ion increases. In this paper, the spectra and laser characteristics of Nd:YSAG single crystal are studied. The (1.5 at.%) Nd3+:Y3Sc2Al3O12 (YSAG) laser crystal is grown by Czochralski method, and X-ray rocking curve shows that the crystal quality is good. The concentration of ions in Nd:YSAG is measured by an electronic probe. The segregation coefficient of Nd3+ ion is calculated to be 0.35, which is approximately twice as much as that of Nd3+ in YAG. The absorption and emission spectra are measured, which indicates that it can be pumped by an 808 nm-laser diode (LD). The strongest emission from the transition 4F3/24I11/2 of Nd:YSAG peaks at 1059 nm with an emission cross section of 1.0310-19 cm2, and the lifetime of 4F3/2 is about 253 s, which indicates that Nd:YSAG has roughly an efficiency equal to that of Nd:YAG, but the laser upper level lifetime is longer than that of Nd:YAG, which is more favorable for Q-switched laser operation. The 808 nm-LD is used to pump Nd:YSAG rod of 2 mm2 mm6 mm, the laser operation with a threshold of 0.85 W and a maximum output power of 1.1 W is realized:the laser slope efficiency is 21.1%, and the optical conversion efficiency is 18.3%. All of the above results show that Nd:YSAG single crystal is a good solid state laser material, which is more favorable for Q-switched laser operation.

Assessment of electron-vibrational interaction (EVI) parameters of YAG:Ce3 +, TAG:Ce3 + and LuAG:Ce3 + garnet phosphors by spectrum fitting method

The electron–vibrational interaction (EVI) in 4f↔5d optical transitions of Ce3+ ions in YAG, TAG and LuAG garnet phosphors have been analysed in this work. The main EVI parameters that have been estimated and reported here are Huang-Rhys factor, effective phonon energy, Stokes shift, red shift and Zero-phonon line position. The EVI parameters were estimated from the room temperature photoluminescence results that were recently reported. The spectrum fitting method was employed to determine the EVI parameters. An emission band was modelled with the aid of the calculated EVI parameters. The agreement between the modelled emission bands with the experimentally obtained ones validated the estimated values of EVI parameters.

Clarifying the preferential occupation of Ga3+ ions in YAG:Ce,Ga nanocrystals with various Ga3+-doping concentrations by nuclear magnetic resonance spectroscopy

Preferential substitution of Ga3+ ions for octahedral Al3+ ions in YAG:Ce,Ga nanophosphors enhances the luminescence properties of Ce3+ activators.

Combined EPR and ODMR study of Ce3+ optical emitters in yttrium aluminium garnet

Electron paramagnetic resonance (EPR) was detected in the ground state of Ce3+ ions in YAG:Ce single crystals by monitoring the intensity of photoluminescence under nonresonant excitation. The photoluminescence intensity was found to increase strongly in magnetic field at liquid helium temperature. The optically detected magnetic resonance (ODMR) effect was of the order of percents and corresponded to resonance decrease in the luminescence intensity. ODMR correlated with the conventional EPR spectra of Ce3+ ions, which occupy the dodecahedral Y3+ sites in the YAG crystal lattice. The increase of the PL intensity in magnetic field was concluded to be caused by Boltzmann distribution between spin sublevels of the ground state of Ce3+ ions. The ODMR tend to equalize the populations of levels in resonance and results to a decrease of PL intensity. Different types of Ce3+ centres characterized by the presence of nearby antisite defects were observed, which should be taken into account in applications of single ion spectroscopy based applications of YAG:Ce.

Electronic structure of Sm3+ ions in YAG and cubic sesquioxide ceramics

A comparative analysis of the low temperature energy level structure of Sm3+ ion in YAG and sesquioxide (Y2O3, Lu2O3, Sc2O3) microcrystalline ceramics, based on new and previously reported data is presented. The Stark level structure of Sm3+ ion is discussed in terms of nephelauxetic and crystal field effects, determined by structural characteristics of the centers (of D2 symmetry for YAG and C2 or C3i for sesquioxides). The Sm3+ electronic structure of C2 centers in sesquioxides presents some peculiarities (barycenters positions, 4F3/2 splitting along the series, etc.), that are correlated to J mixing effects, important for low symmetry systems and increasing from Y2O3 to Sc2O3. The energy levels of Sm3+ in centrosymmetric C3i centers in Sc2O3, obtained by a time-resolved technique, along with the previous reported data on sesquioxides are also analyzed.

Photoconductivity in Yb-doped oxides at high excitation densities

Photoconductivity has been found in the dielectric laser materials Yb3+:YAG and Yb3+:Lu2O3 under 940 nm irradiation with an unexpected high photocurrent up to several 100 nanoamperes. The nonlinear intensity dependence points to the occurrence of a cooperative upconversion mechanism with 2–3 excited Yb3+-ions in YAG and 2 excited Yb3+-ions in Lu2O3 being involved. According to the results two tentative models of this upconversion process are discussed.

Magnetooptics of the 1 D 2 → 3 F 4 radiative transition in thulium:yttrium-aluminum garnet Tm3+:YAG

The spectra of luminescence and magnetic circular polarization of luminescence in the 1 D 2 → 3 F 4 emission band in thulium:yttrium-aluminum garnet Tm3+:YAG (Tm3+:Y3Al5O12) have been investigated at temperatures T = 78 and 293 K, respectively. Based on the analysis of the magnetooptical and optical spectra, the optical transitions between the Stark sublevels of the 3 F 4 and 1 D 2 multiplets in Tm3+:YAG were identified. It is shown that the symmetry and energies of the Stark sublevels of the 3 F 4, 1 D 2, and 3 H 6 multiplets, found experimentally from magnetic and magnetooptical studies, confirm the results of theoretical calculations of the energy spectrum of the rare earth Tm3+ ion in YAG.

Spontaneous and induced emission in dielectric nanoparticles

An analytical expression is proposed for the rate of radiative decay of excitations of optical centers in an ellipsoidal nanoparticle that is considerably smaller than the light wavelength (a, b, c ≪ λ) and is embedded in the surrounding medium. This expression is compared with the corresponding expression for a bulk crystal. The time of radiative decay in nanoparticles spherical in shape and identical in size (2R ≪ λ) is derived as a function of the dielectric characteristics of a nanocomposite and the nanoparticle volume fraction C in suspensions and aerosols. The expressions describing the emission and absorption cross sections in spherical nanoparticles are obtained. The experimentally measured and theoretically calculated decay times of metastable levels of rare-earth impurity ions in YAG and Y2O3 crystalline nanoparticles are compared with those for bulk crystals with the same structure.

Luminescence studies on lanthanide ions (Eu 3+, Dy 3+ and Tb 3+) doped YAG:Ce nano-phosphors

Yttrium aluminum garnet nanoparticles both undoped and doped with lanthanide ions (Ce 3+, Eu 3+, Dy 3+ and Tb 3+) having average size around 30 (±3 nm) nm were prepared by glycine nitrate combustion method followed by annealing at a relatively low temperature of 800 °C. Increase in the annealing temperature has been found to improve the luminescence intensity and for 1200 °C heated samples there exists strong energy transfer from Tb 3+ to Ce 3+ ions in YAG:Ce(2%),Tb(2%) nanoparticles as revealed by luminescence studies. Co-doping the YAG:Ce nanoparticles with Eu 3+ results in significant decrease in the emission intensity of both Ce 3+ and Eu 3+ ions and this has been attributed to the oxidation of Ce 3+ to Ce 4+ and reduction of Eu 3+ to Eu 2+ ions. Dy 3+ co-doping did not have any effect on the Ce 3+ emission as there is no energy transfer between Dy 3+ and Ce 3+ ions.

Luminescence of Pb2+ ions in YAG:Pb single‐crystalline films

AbstractLuminescence of Pb2+ ions in YAG:Pb single‐crystalline films (SCF) with different lead content in the range of 0.01–0.3 at% was investigated by means of cathodoluminescence, time‐resolved emission/excitation spectra and luminescence decay kinetic under excitation by synchrotron radiation. The nature of Pb2+ ion‐related emission bands in the UV and visible ranges and their prevailing excitation mechanism are considered. Strong mixing of the 1P1 excited states of Pb2+ ions and the conduction‐band states of the YAG host was found. A scheme of energy levels of Pb2+ center in YAG and LuAG is presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Temperature dependence of spectral-line intensities in YAG:Yb3+

On the basis of the detailed calculation of the matrix elements of the interaction of an optical electron of an impurity ion with lattice phonons taking into account the nonadibatic contributions, the Debye-Waller factors, homogeneous widths, and the shifts of no-phonon spectral lines of Yb3+ ion in YAG are calculated. The temperature dependences of the intensities of the most intensive spectral lines are obtained. It is shown that with a decreasing temperature, the intensities of the spectral lines on the wavelengths 968.3 and 1030 nm are sharply increased.

Luminescence of [formula omitted] ions in [formula omitted] single crystalline films

The absorption and cathodoluminescence spectra of single crystalline films (SCF) of Y 3 Al 5 O 12 : Bi garnet depending on Bi concentration were analyzed. For consideration of the nature of the UV and visible Bi-related emission bands the time-resolved luminescence of Bi 3 + ( ns 2 ) ions in YAG:Bi SCF was studied at 10 K under excitation by synchrotron radiation. The difference in the excitation spectra and emission decay of the UV and visible bands has been explained via radiative relaxation from the P 1 , 0 3 excited states to the S 0 1 ground state of the isolated and pair/clustered Bi 3 + emission centers in the garnet lattice, respectively.

Luminescence studies of Ce:YAG using vacuum ultraviolet synchrotron radiation

Photoluminescence spectrum of Ce:YAG single crystal was studied employing vacuum ultraviolet (VUV) synchrotron radiation. Intrinsic absorption edge at about 52,000 cm −1 was observed in the absorption spectrum. From the VUV excitation spectrum, the energy of the highest d-component of 53,191 cm −1 (188 nm) for the Ce 3+ ions in YAG was obtained at 300 K. The disappearance of the third 5d level at 37,735 cm −1 (265 nm) in absorption and excitation spectra in our samples may be due to the impurity Fe 3+ ions absorption.

Energy Spectrum of YAG:Cr3+ and Thermal Shifts of Its R Lines

Traditional ligand-field theory has to be improved by taking into accountboth ``pure electronic'' contribution and electron-phonon interaction one(including lattice-vibrational relaxation energy). By means of improvedligand-field theory, R1, R2, R'3, R'2, and R'1lines, U band, ground-state zero-field-splitting (GSZFS) and ground-state gfactors as well as thermal shifts of R1 line and R2 line ofYAG:Cr3+ have been calculated. The results are in very good agreementwith the experimental data. In contrast with ruby, the octahedron of ligandoxygen ions surrounding the central Cr3+ ion in YAG:Cr3+ iscompressed along the [111] direction. Thus, for YAG:Cr3+ and ruby,the splitting of t23 4A2 (or t23 2E) has opposite order,and the trigonal-field parameters of the two crystals have opposite signs.In thermal shifts of R1 and R2 lines of YAG:Cr3+, thetemperature-dependent contributions due to EPI are dominant.

Growth and spectroscopic analysis of Yb3+-doped Y3Al5O12 fiber single crystals

Two major fiber crystal growth methods have been applied for the synthesis and spectroscopic characterizations of Yb3+-doped Y3Al5O12 (Yb:YAG) to show the feasibility of a flexible single crystal fiber laser. One is the micropulling-down (μ-PD) method and the other is the laser heated pedestal growth (LHPG) method. 500 mm length fiber with no Yb segregation has been grown by the μ-PD method. A detailed analysis of Yb:YAG spectroscopy is made to contribute to the discussion on the determination of energy levels. On the other hand, a combinatorial chemistry approach has been applied on concentration gradient crystal fibers grown by the LHPG method allowing the measurement of the intrinsic radiative lifetime and the analysis of concentration quenching processes of Yb3+ ions in YAG.

Charge transfer fluorescence and f–f luminescence in ytterbium compounds

Abstract Luminescence and excitation spectra as well as decay kinetics are presented for the charge transfer (CT) luminescence of Lu 3 Al 5 O 12 , Y 3 Ga 5 O 12 and YAlO 3 crystals doped by Yb 3+ in various concentrations, the CT luminescence properties are compared to those of Y 3 Al 5 O 12 –Yb. For the first time the excitation spectra of the intraconfigurational 2 F 5/2 → 2 F 7/2 luminescence of Yb 3+ ions in YAG, LuAG and YAP in the region of the CT absorption band and in the fundamental absorption range up to 20 eV were measured, possible mechanisms of the energy transfer to Yb 3+ 4f states are discussed.

Temperature dependencies of excited states lifetimes and relaxation rates of 3–5 phonon (4–6 μm) transitions in the YAG, LuAG and YLF crystals doped with trivalent holmium, thulium, and erbium

Abstract The temperature dependencies of the nanosecond multiphonon relaxation (MR) rates of the 3 F 3 state of Tm3+ in the YLF crystal and of the 5 F 5 state of Ho3+ ion in the YAG and LuAG crystals and of the microsecond MR rates of the 4 F 9/2 ( 2 H 9/2 ) state of Er3+ ions in YLF were measured in the wide temperature range using direct laser excitation and selective fluorescence kinetics decay registration. For YLF the observed relations are explained by 4-phonon process in the frame of a single-frequency model with hω eff =450±30 cm −1 for the 3 F 3 state of Tm3+ and by 5-phonon process with hω eff =445 cm −1 for the 4 F 9/2 ( 2 H 9/2 ) state of Er3+. For YAG and LuAG crystals these dependencies are explained by the 3-phonon process with hω eff =630 cm −1 . The decrease of the relaxation rate with the temperature in the range from 13 to 80 K was observed for the 4 F 9/2 ( 2 H 9/2 ) state of Er3+ in the YLF crystal. It is explained by the redistribution of excited electronic states population of erbium ions over the higher lying Stark levels with different MR probabilities. A good fit of experimental temperature dependence (including the dropping part of the experimental curve) was obtained for single-frequency model ( hω eff =450 cm −1 ) with W 01 =8.0×10 4 s −1 and W 02 =4.7×10 4 s −1 accounting Boltzmann distribution of population over two excited Stark levels of the excited state of erbium ions. Employment of this model improves the fit between the experiment and the theory for the 5 F 5 state of Ho3+ ion in YAG as well. Strong influence of the parameters of the non-linear theory of MR, i.e. the reduced matrix elements U(k) of electronic transitions and the phonon factor of crystal matrix η on the spontaneous MR rates was observed experimentally. The smaller these parameters the slower the spontaneous MR W0. This fact can be used for searching new active crystal laser media for the mid-IR generation.

Effects of energy back transfer on the luminescence of Yb and Er ions in YAG

The back-energy-transfer process from acceptors to donors is included to predict and explain the nonradiative energy-transfer processes among Yb–Er ions in a YAG matrix. This process is in addition to the direct Yb-to-Er energy transfer and the migration of energy among Yb ions. The two measured Yb transients are well fitted by the corresponding solution of the master equations that give the dynamics of the energy-transfer processes.