LiYF4 Crystals Research Articles

VUV luminescence of Er3+ ions in LiYF4 and BaY2F8 crystals

Vacuum ultraviolet luminescence of Er3+ ions in LiYF4 and BaY2F8 crystals has been investigated. It is revealed that under excitation by 193 nm radiation from an ArF excimer laser the interconfigurational 5d–4f radiative transitions in Er3+ ions are observed. It is shown that from the LiYF4:Er crystal only the spin-forbidden luminescence (λ = 165 nm) is detected, whereas both the spin-forbidden (λ = 169 nm) and spin-allowed (λ = 160.5 nm) components are observed from the BaY2F8:Er crystal.

Ab initio lattice relaxation and electronic structures of LiYF4 crystals containing VF color center

Abstract The electronic structures of perfect LiYF4 and the LiYF4 containing lithium vacancy VLi− with the lattice structure optimized are studied within the framework of the density functional theory. By analyzing the lattice relaxation and electronic structure of the LiYF4 containing VLi− we can reasonably believe that once VLi− is formed in LiYF4 crystal, its compensating hole will turn out to be shared by two F− nearest to VLi− forming a diatomic fluoride molecular ion (F2−) perturbed by VLi−, or to say VF color center. According to the molecular-orbital linear combination of atomic orbital (MO-LCAOs) theory, compared to the alkali halides, e.g. LiF, the F2− in VF center in LiYF4 peaks at about 337 nm, which is in agreement with the experimental results.

Multi-range high-frequency EPR spectroscopy of LiYF4 and LiLuF4 crystals doped by rare-earth ions

EPR spectra of isostructural LiYF4 and LiLuF4 crystals doped by Dy3+, Er3+, and Ho3+ ions are measured at 4.2 K in the frequency range 40–800 GHz. The effects caused by isotopic disorder in the lithium sublattice, the random crystal field, and the interaction between paramagnetic impurity ions are detected and studied. The results of the measurements are used to determine the spectral characteristics of the compounds and the crystal field parameters. It is demonstrated that the formation of the isotope structure of the EPR signal is dominated by local deformations of the crystal lattice induced by mass defects.

Lines of Ho3+-Ho3+ pair centers in optical spectra of LiYF4 and LiLuF4 crystals

The high-resolution spectra of LiYF4 and LiLuF4 crystals doped with holmium are studied. It is shown that the weak satellites of some principal lines observed in the optical spectra belong to Ho3+-Ho3+ pair centers. The role played by local crystal-field distortions in the formation of the spectrum of pair centers is verified experimentally.

Investigation of the up-conversion processes in Er3+:LiYF4 crystals 12

In this work, we investigated the up-conversion processes in LiYF4 (YLF) crystals doped with 1 mol% of Er3+ and containing 50 mol% of Er3+. The up-conversion processes include the excited state absorption (ESA) of pumping radiation process and the energy-transfer up-conversion (ETU) process. The luminescence lifetime was measured from decay curve of the 4S3/2 T 4I15/2 (556 nanometers [nm]) transition using pulsed laser excitations tuned between 967 and 999 nm from an optical parametric oscillator pumped by the second harmonic of a Q-switched Nd:YAG laser. We also studied the dipole-dipole and dipole-quadrupole interactions that occur among Er3+ ions in Er (50 mol%):YLF crystal. For this investigation, we used the Inokuti-Hirayama model that is due to an energy transfer between ions without involving the excitation migration through donors.

<strong>Investigation of the up-conversion processes in Er3+:LiYF4 crystals 12</strong><br> DOI: 10.5585/exacta.v4i1.662

In this work, we investigated the up-conversion processes in LiYF4 (YLF) crystals doped with 1 mol% of Er3+ and containing 50 mol% of Er3+. The up-conversion processes include the excited state absorption (ESA) of pumping radiation process and the energy-transfer up-conversion (ETU) process. The luminescence lifetime was measured from decay curve of the 4S3/2 T 4I15/2 (556 nanometers [nm]) transition using pulsed laser excitations tuned between 967 and 999 nm from an optical parametric oscillator pumped by the second harmonic of a Q-switched Nd:YAG laser. We also studied the dipole-dipole and dipole-quadrupole interactions that occur among Er3+ ions in Er (50 mol%):YLF crystal. For this investigation, we used the Inokuti-Hirayama model that is due to an energy transfer between ions without involving the excitation migration through donors.

Laser-polarimetric measurements of magnetic ac-susceptibility in LiYF4: Ho3+ crystals

Laser-polarimetric technique with the shot-noise-limited polarimetric sensitivity is used to study magnetic ac-susceptibility in holmium doped LiYF4 crystals in the range of Zeeman energies comparable with that of the hyperfine interaction in Ho3+ ions. Specific features of optical methods of magnetic measurements, the experimental setup, and results of measurements are discussed. Polarimetric sensitivity of the setup (∼10−8 rad) allowed us to measure the ac-susceptibility of LiYF4 single crystals containing 0.1–0.3 mol % of impurity Ho3+ ions with the signal-to-noise ratio exceeding 102. The obtained field-strength and frequency dependences of the ac-susceptibility show that the resonant peaks of the susceptibility mainly result from cross-relaxation transitions between the electronic-nuclear sublevels of Ho3+ ions.

Growth of YLF:Yb:Tm:Nd for optical applications

The focus of this study is the behavior of Tm, Yb and Nd ions in the LiYF4 (YLF) crystal. One YLF crystal was successfully grown by the Czochralski method; it was doped with 20 mol% Yb, 1.3 mol% Nd and 0.05 mol% Tm. The segregation coefficients of the dopants and lattice parameters were determined. The spectroscopic properties of samples with different amounts of Nd were obtained from absorption and emission studies.

γ-Ray induced color centers in pure and Yb doped LiYF4 and LiLuF4 single crystals

c-Ray irradiation was used to carry out a comparative study of the induced optical absorption phenomena and color center creation in the ultraviolet and visible spectral regions. The F-center absorption band at 315 and 330 nm in LiLuF4 and LiYF4, respectively, is the dominating induced absorption feature. The amplitude of the induced absorption is reduced by more than a factor of 3 in Yb-doped crystals compared to the undoped ones. Comparison was made with other fluorides, such as CaF2 ,K Y 3F10 and BaY2F8. In Yb-doped CaF2, LiLuF4, LiYF4, BaY2F8 and KY3F10 we observed arising of two possible types of Yb 2+ centers after c-ray irradiation. For the entire materials exclude KY3F10 we found Yb 2+ centers related to Yb 3+ , as an effect of recharging one of Yb 3+ ion from pair, while for KY3F10 we found mainly Yb 2+ centers related to isolated Yb 3+ ions, as an effect of Compton electron capturing by isolated Yb 3+ ion.

Spectral Kinetics of Ce[sup 3+] Ions in Double-Fluoride Crystals with a Scheelite Structure

The influence of the cation composition on the spectral kinetics of Ce3+ ions in double-fluoride crystals with a scheelite structure is studied. The importance of the photodynamic processes induced in these crystals by the exciting radiation is demonstrated. The difference in luminescence quantum efficiency between Ce3+ ions in LiYF4 and LiLuF4 crystals is found to be due to the different lifetimes of color centers produced in the samples by the exciting radiation and to the different efficiency of the free-carrier recombination at cerium impurity centers. It is shown that Yb3+ ions can increase the carrier recombination rate in the crystals.

Low-temperature high-resolution VUV spectroscopy of Ce3+ doped LiYF4, LiLuF4 and LuF3 crystals

Low-temperature high-resolution VUV spectroscopy of Ce3+ doped LiYF4, LiLuF4 and LuF3 crystals

Low-temperature high-resolution VUV spectroscopy of Ce3+ doped LiYF4, LiLuF4 and LuF3 crystals

For LiYF4:Ce3+, LiLuF4:Ce3+ and LuF3:Ce3+ crystals UV/visible emission and time-resolved VUV/UV excitation spectra were recorded at liquid helium temperature with spectral resolution of 0.1nm for excitation spectra and better than 0.3nm for emission spectra. Well resolved fine structures due to zero-phonon lines were clearly observed in both excitation and emission spectra for LiYF4:Ce3+ and LiLuF4:Ce3+. For LuF3:Ce3+ crystal no fine structure was detected in the spectra even at the highest spectral resolution. Under the host excitation, the fine structure for high-energy emission band of Ce3+ (5d–2F5/2) in LiLuF4:Ce3+ becomes well pronounced because of weaker reabsorption effect, as compared to Ce3+ 4f–5d absorption, due to small penetration depth for exciting radiation. As a result the crystal-field splitting for 2F7/2 and 2F5/2 levels of Ce3+ in LiLuF4 crystal was measured. First observation of zero-phonon lines at ∼81,550 and ∼82,900cm−1 as well as vibronic side bands due to interconfigurational 4f14–4f135d transitions in Lu3+ is reported for excitation spectrum of LiLuF4:Ce3+.

First-principles analysis method for the multiplet structures of rare-earth ions in solids

A first-principles fully relativistic multielectron method based on molecular orbital (MO) theory is applied to the analysis for the 4f5d configurations of Pr3+-doped LaF3, LiYF4 (YLF), and CaF2 crystals. The formation of MOs between the Pr 5d orbitals and the ligand fluorine 2p orbitals is considered using a (PrF11)8− and (PrF8)5− molecular models. The energy of the lowest level of 4f5d configuration decreases in the order LaF3, LiYF4, and CaF2 (Oh symmetry). The high energy in Pr3+:LaF3 is ascribed to the smaller ligand-field splitting due to the large coordination number. The analysis of many-electron wave functions shows the mixtures between the spin-orbit splitting of the 4f-level MOs and the ligand-field splitting of the 5d-level MOs. Configuration interaction with one-electron excitations gives transition probability to the originally forbidden two-electron excitations, which produce satellite structures in spectra.

Investigation of the multiphoton excitation process of the 4f 25d configuration in LiYF4 and LiLuF4 crystals doped with trivalent neodymium ion

Ultraviolet (UV) fluorescence of Nd3+ ions induced by multistep laser excitation was investigated in Nd-doped LiYF4 and LiLuF4 crystals using a technique of time-resolved spectroscopy. The observed UV luminescence was due to transitions between the bottom of 4f25d configuration and the 4f3 states of Nd3+ ions. The first absorption band of 4f25d configuration, which starts around 56 700 cm−1, was excited by three stepwise absorptions of photons in the green (500–535 nm) from a short pulse laser excitation leading to broad emission bands in UV range (180–280 nm). An excitation band in the blue (468–486 nm) was observed due to the excitation of the second absorption band of 4f25d configuration around 63 000 cm−1 according to the photon absorption sequence: I9/24+hν(480 nm)→2G(1)9/2+hν(480 nm)→2F(2)7/2+hν(480 nm)→4f25d(second). The observed UV emissions (180–280 nm) from the bottom of the 4f25d configuration (first state) have a lifetime of 35 ns (parity allowed) and are broadband in contrast to UV emissions from 4f3 configuration, which are also present in the luminescence investigation but having a longer lifetime (8.5 μs) and structures composed of narrow lines. The excitation spectrum of fast UV luminescence exhibited different structures depending on the excitation geometry (σ or π) with respect to the c axis of the crystal. We observed two emissions from the first state of 4f25d configuration with peaks at 535 and 595 nm modifying the luminescence branching ratio of the bottom of the 4f25d configuration around 55 500 cm−1. The equivalent cross section of three and two excitation processes was estimated at 510 nm by solving the rate equations of the system under short laser excitation, which shows that is possible to have laser action under pulsed laser pumping with intensity below the crystal damage threshold.

Energy Level Structure of LiYF<SUB>4</SUB>:Dy<SUP>3+</SUP>: Crystal Field Analysis

Crystal field analysis of the energy level structure of lithium yttrium fluoride doped with trivalent dysprosium was performed. Assignment of absorption lines in experimental spectrum of absorption was made in a wide spectral region: from IR to UV. Crystal field parameters for the whole series of trivalent rare earth ions in LiYF4 crystal were obtained. The values of the intermediately coupled Lande g-factor were calculated and used to estimate the EPR g-factors g||, g⊥ for LiYF4:Dy3+.

Theoretical analysis and intensity calculation for the f → d absorption spectrum ofU3+ inthe LiY F4 crystal

The absorption spectrum of U3+ in LiY F4 has been well calculated using the model proposed by Reid for calculations of spectra. The relevant formulae for the matrix element calculations which wereomitted in this model are now described in detail, and the values of the direct andexchange coefficients associated with the f–d Coulomb interactions within thef2d configuration are derived and listed. The amount of reduction for the f–d Coulombinteraction parameters from the free-ion values is found to be , which is much larger than the value of 26% for the isoelectronicNd3+ lanthanide ion in the same host.

Interpretation of the optical spectra and EPR parameters for Yb3+ in LiYF4 crystal

AbstractIn this paper, the crystal‐field energy levels, the EPR g‐factors g∥, g⟂ of Yb3+ and hyperfine structure constants A∥, A⟂ of 171Yb3+ and 173Yb3+ isotopes in LiYF4 crystal are calculated from the crystal‐field theory. All the calculated results (seven energy levels and six EPR parameters) are in reasonable agreement with the observed values. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical Investigations of the Electron Paramagnetic Resonance g Factors for the Trivalent Cerium Ion in LiYF4 Crystal

The perturbation equations of the EPR parameters g‖ and g⊥ for the lowest Kramers doublet of a 4f1 ion in tetragonal symmetry are established. In these equations, the contributions of the covalency effects, the admixture between J = 7/2 and J = 5/2 states and the second-order perturbation (which is not considered previously) are included. The crystal field parameters for the studied Ce3+ center are calculated from the superposition model. Based on the above perturbation equations and related parameters, the EPR g factors for the Ce3+ center in LiYF4 crystals are reasonably explained. The results are discussed.

Theoretical investigation of 4f3↔4f25d transitions in Nd3+:LiYF4 crystal

Abstract A theoretical investigation of the Nd 3+ 4f 3 ↔ 4f 2 5d interconfigurational transitions in the tetragonal Nd 3+ :LiYF 4 crystal is performed. The calculation reproduces quite well the spectral shape as well as the intensity of the experimental spectra. Moreover, it is found that the absorption maximum moves toward higher 4f 2 5d energies when the chosen initial 4f 3 sublevel itself shifts to higher energies. This behaviour is explained as a total or partial “memory” during the optical transition for the expectation values of different terms of the electronic Hamiltonian, especially the electrostatic ones.

Picosecond lifetimes and infrared spectroscopy of hydrogenic sites in KY3F10 and LiYF4

A single H− site with axial symmetry is observed for LiYF4 crystals while two distinct H− sites of axial and rhombic symmetry are observed for KY3F10 crystals. Infrared pump–probe measurements yield 10K lifetimes of 2.7 and 14ps for the axial H− sites in LiYF4 and KY3F10, respectively. The temperature dependence of relaxation processes for these H− modes is modelled on a combination of anharmonic phonon decay and elastic-phonon scattering processes.