YVO4 Single Crystals Research Articles

Evaluation of photoluminescence and scintillation properties of Eu-doped YVO4 single crystals synthesized by optical floating zone method

0.1, 0.5, 1.0, and 5.0 % Eu-doped YVO4 single crystals were fabricated to assess photoluminescence (PL) and scintillation properties. The powder X-ray diffraction patterns of all the fabricated samples were the same as that of reference, and a single-phase structure of YVO4 was observed. The emission peaks owing to the 4f-4f transitions of Eu3+ ions were observed at 590, 605, 615, 620, and 695 nm in PL and scintillation spectra. Based on the pulse height spectra, Eu-doped samples had the light yield of 28,000 (0.1 % Eu), 33,000 (0.5 % Eu), 42,000 (1.0 % Eu), and 37,000 (5.0 % Eu) photons/MeV. In afterglow profiles, the afterglow level of 0.1, 0.5, 1.0, and 5.0 % Eu-doped samples was 58.1, 61.1, 49.1, and 35.6 ppm.

Effect of Cr co-doping on the optical absorption and emission characteristics of Yb:YVO4 single crystals grown by OFZ technique

Cr co-doped Yb:YVO4 (Cr:Yb:YVO4) single crystals with concentrations of 1.0 and 1.5 at.% of Cr and 3.0 at.% of Yb were grown by the optical floating zone technique. X-ray diffraction analysis on the grown crystals revealed that the lattice parameters of Cr:Yb:YVO4 crystals do not depend on the Cr doping concentration. The dislocation etch pit density estimated from the etching study was found to be 103/cm2. The observed fringes of nearly uniform thickness and spacing in birefringence interferometry for [100] plate and conoscopy pattern for [001] plate indicate the compositional and optical homogeneity of the crystal. Further, the influence of the Cr doping concentration on the 2A1→2B2 transition (at ∼1100 nm) and 2A1→2E transition (at ∼640 nm) due to Cr5+ ion were analysed using two orthogonal polarized light with electric field perpendicular (π-polarization) and parallel (σ-polarization) to [001] axis. These absorption peaks of Cr ion were found to be sensitive to the polarization of incident light. The absorption transition 2A1→2B2 around 1100 nm are permitted for π-polarization and on the other hand, the absorption transition 2A1→2E at 640 nm are permitted only for σ-polarization. The characteristic broader absorption band around ∼1100 nm is of importance as it is useful for self-Q-switching in a laser gain medium. The absorption coefficient corresponding to Cr5+ ions at 1100 nm increases with the increase in Cr doping concentration. The band-gap for σ-polarized light is slightly higher than π-polarized light and decreases with Cr doping. The increase in the estimated Urbach energy (50–122 meV) with the increase in the Cr doping concentration confirms that the defect states close to the band edge increase thus decrease the band gap. Further the photoluminescence intensity is in-line with the absorption data and decreases with increase in the Cr concentration from 0 to 1.5 at.%.

Photoluminescence characteristics and energy transfer phenomena in Ce3+-doped YVO4 single crystal

Abstract The undoped YVO4 and Ce3+-doped YVO4 single crystals have been successfully grown by the Czochralski method in a medium frequency induction furnace. The X-ray diffraction patterns testified that all samples exhibited the pure tetragonal YVO4 crystalline phase without any parasitic phases. The optical properties of Ce3+-doped YVO4 single crystals with different doping concentrations were investigated via a combination of absorption, emission, and excitation spectra. Dependence of luminescence and absorption intensity on Ce3+ doping concentration was discussed at different excitation wavelengths. The typical transitions of Ce3+ ions and the unusual intrinsic luminescent phenomena of VO 4 3 − {\text{VO}}_{4}^{3-} groups were observed and investigated in Ce3+-doped YVO4 crystals. More attentions were paid to ascertaining the corresponding transition states, analyzing luminescent mechanism, and revealing the energy transfer from VO 4 3 − {\text{VO}}_{4}^{3-} to Ce3+ ions. In addition, the CIE chromaticity coordinates and correlated color temperature were calculated on a basis of emission spectra under different excitation wavelengths.

Investigation of optical and spectroscopic properties of Nd co-doped Yb:YVO4 single crystals grown by OFZ method

Nd (0.8 at.%) co-doped Yb (0.8 and 3.0 at.%):YVO4 single crystals were grown by optical floating zone technique for the first time to the best of our knowledge. The absorption spectra revealed strong absorption for π-polarization (E||c) than the σ-polarization (E⊥c) for both the Yb concentrations due to anisotropy of the crystal. The estimated effective Judd-Ofelt parameters are 11.8675 × 10−20, 5.1577 × 10−20 and 7.3755 × 10−20 cm−2. Spectroscopic quality factor of Nd co-doped Yb:YVO4 are 0.70. which is lower than that of Nd (1.0 at.%) doped YVO4 (0.97), which indicates the energy transfer from Nd3+ ion to Yb3+ ion inside the host matrix. The estimated emission cross-section of 4F3/2 → 4I11/2 Nd transition with an excitation at 808 nm for both the concentrations of Yb is ∼4.0 × 10−19 cm2 which is almost same as estimated by Bhaumik et al. (2014) [21] for Nd:YVO4. Hence emission cross-section of 4F3/2 → 4I11/2 Nd transition is not effected by Yb co-doping. Also the PL intensity of Yb at 1010 nm enhances with Yb co-doping for same Nd (0.8 at.%) this is because the Nd3+ ion effectively excites the Yb3+ ion in upper state. Therefore Nd3+ ion acts as excellent sensitizer for Yb:YVO4 laser gain medium and make efficient pumping in the gain medium.

Growth and optical investigation of Nd co-doped Yb:YVO4 crystal: A promising material for laser gain medium

Abstract Nd co-doped Yb:YVO4 single crystals were grown for the first time by using optical floating zone method to the best of our knowledge. The dimension of grown crystals were ~4–5 mm in diameter and 10–15 mm in length. Powder crystal XRD shows that there is a small shift of diffraction peaks towards the lower angle with Nd doping in the crystal, signifying the expansion of the lattice volume. The quality of the crystal was estimated by Rocking curve measurement. The observed nearly straight fringes in birefringence interferogram ensured the good optical homogeneity of grown crystals. The variation in birefringence was found to be less than 5.64 × 10−4. The dislocation etch pit density was estimated by chemical etching and found to be ~12 × 103/cm2. The measured fluorescence life-time of Yb (0.8 at.%) and Nd (0.8 at.%) co-doped YVO4 crystal is around 581 and 66 μs respectively. The polarized absorption spectra depicted an overall higher absorption for π-polarization (E||c) than the σ-polarization (E┴c). The absorption coefficient at 808 nm & 985 nm corresponding to Nd (0.8 at.%) & Yb (0.8 at.%) ions are ~ 28 & 9.2 cm−1 for π-polarization and ~13.7 & 4.6 cm−1 for σ-polarization, respectively, which is found to be better than the crystals grown by conventional Cz technique. However, the fluorescence lifetime of the crystal grown by OFZ and Cz technique is similar. The present findings revealed that π-polarized absorption of Nd ion at 808 nm can be effectively utilized for pumping Yb:YVO4 gain medium for developing an efficient laser system.

Investigation of neodymium doped YVO4 by EPR method

Crystal field parameters of neodymium impurity centers in YVO4 single crystals were determined using data of CW EPR spectroscopy and the known energy level schemes. The spin echo spectroscopy was used to determine spin-lattice and spin-spin relaxation times of the 143Nd3+ and 145Nd3+ impurity ions in YVO4 single crystal.

Effect of Yb co-doping on the spectral properties of Er:YVO4 single crystal: A Judd Ofelt analysis

Single crystals of 0.7 at% Er:YVO4 co-doped with varied concentrations of Yb (1.5, 3.0 and 8.0 at%) were grown by optical floating zone technique. The absorption spectra of the grown crystal are characterized by the prominent absorption at 985 nm due to Yb ion and multiple absorption due to Er ions. The overall characteristic absorption for π-polarization (E||c) is stronger than that for σ-polarization (E┴c) due to alignment of dipole moments along c-direction. The line strength of all the transitions of Er ions decreases as the doping concentration of Yb increases. Judd Ofelt parameter Ω2, which strongly depends on the environment of ligand, decreases with increasing Yb concentration in the lattice. The value of spectroscopic quality factor was found to be nearly invariant (~ 1.80) with respect to the Yb doping concentration but better than that for Er doped YVO4 (~1.31) [1]. The radiative lifetime and emission cross-section of 4I13/2→4I15/2 transition of Er ions was also found to be independent of Yb doping concentration. This is one of the biggest advantages of Yb co-dopant as a good sensitizer in the Er:YVO4 as it results in high population density in upper level of Er ions making it. The emission cross-section of 4I13/2→4I15/2 line for excitation at 985 nm is ~ 2.33 × 10−20 cm2. Further, the values of emission cross-section for both the excitation at 808 nm (Er absorption line) and 985 nm (Yb absorption line) were found nearly same.

Effect of Yb doping on the refractive index and thermo-optic coefficient of YVO4 single crystals.

Single crystals of YVO4 with different doping concentrations of Yb (1.5, 3.0, 8.0, and 15.0 at. %) and with good crystalline quality (FWHM ∼43-55 arc sec of rocking curve) were grown by the optical floating zone technique. Refractive index measurements were carried out at four wavelengths as a function of temperature. The measurements show that as the doping concentration of Yb is increased, the refractive index varies marginally for ne whereas there is a significant change in the value of no. The thermo-optic coefficient (dn/dT) was found to be positive with a value ∼10-5/°C, which is 1 order higher than that for the undoped YVO4 crystal. The thermo-optic coefficient is higher for ne compared to that of no. Also, a set of relations describing the wavelength dependence of the thermo-optic coefficient were established that are useful for calculating the thermo-optic coefficient at any temperature in the range 30°C-150°C and at any wavelength in the range 532-1551 nm.

Magnetic field induced extraordinary photoluminescence enhancement in Er3+:YVO4 single crystal

A bright green photoluminescence (PL) from 4S3∕2 → 4I15∕2 emission band in Er3+:YVO4 single crystal has been observed with the excitation of an argon laser at 488.0 nm. More than two orders of PL enhancement have been obtained under the effect of magnetic fields, and the enhancement factor f reaches 170 when the applied magnetic field is 7.7 T under the sample temperature of 4.2 K. Unusually, the PL enhancements only happen at some certain magnetic fields (Bcs), and a decrease of sample temperature will lead to the increase of f and decrease of Bc. The results confirm that this PL enhancement originates from the resonance excitation of the electron transitions induced by the cross of the laser energy and the absorption energy modulated by both the magnetic field and temperature. This special PL enhancement in Er3+:YVO4 single crystal can be applied in the calibration of pulsed high magnetic field, detection of material fine energy structures, and modulation of magneto-optical devices.

Investigation of thermal diffusivity dependence on temperature in a group of optical single crystals doped with rare earth ions

The group of YAG, YVO4 and GdCOB single crystals was examined to determine the thermal diffusivity as a function of temperature in range from 30°C to 300°C. Further investigations concerned on analysis of the influence of dopants on these dependencies. The experimental setup based on thermal wave method with mirage detection was used. The samples represented different crystallographic systems such as cubic (YAG) tetragonal (YVO4) and monoclinic (GdCOB). The anisotropy of thermal conductivity of investigated samples was taken into account in the investigations. The crystals were doped with calcium ions, rare earth ions such as ytterbium, neodymium, and thulium, and also with transition metal vanadium. The results confirmed that influence of doping on the thermal diffusivity of investigated materials strongly depends on temperature. In general the thermal diffusivity decreases with increasing of sample temperature from 30°C to 300°C, however the drop in thermal diffusivity is the highest for pure single crystals. Doping is another factor reducing the heat transport in single crystals. Introduction of dopant ions into a crystal lattice leads to a significant decrease in the thermal diffusivity at lower temperatures in comparison with pure crystals. However, the influence of dopants becomes less pronounced with increasing temperature,and in case of weakly doped crystals it becomes negligible at higher temperatures. The interpretation of thermal diffusivity dependence on temperature for single crystals was based on the Debye model of latticethermal conductivityof solids. The results allowed to conclude that the decrease of thermal diffusivity with temperature and increasing concentration of impurities is caused by shortening of the phonons mean free path due to phonon–phonon and phonon-point defect scatterings.

Structural and Spectroscopic Characterization of Nd3+-Doped YVO4Yttrium Orthovanadate Nanocrystallites

Yttrium orthovanadate (YVO4) nanoparticles doped with Nd3+ ions (0.1–10 mol %), thermally treated at 700 to 1000 °C for 3 h were prepared using modified Pechini’s technique. The structure of products were studied using standard X-ray diffraction (XRD) technique and Rietveld method. The average particle size was found to be about 20 nm (both XRD and transmission electron microscopy) for samples annealed at 700 °C, and further rapid growth was noticed above 900 °C. The spectroscopic behavior of the Nd3+:YVO4 was studied in detailed based on the absorption, excitation, emission, and decay times measurements. The effect of the dopant concentration on progressive increase of reabsorption process and emission concentration quenching was observed. The size effect was manifested in the change of the relative intensities ratio for the resonant and laser transitions. In order to explain reverse behavior of the resonant line comparative studies with the Nd3+:YVO4 single crystal were conducted. An increase of synthetic parameters, concentration of Nd3+ cations and sintering temperature, leads to emission spectra comparable with the grinded single crystal.

Crystal field splitting and effective g factor of infrared emission band in [formula omitted] single crystal

Strong multiple emission lines in 1550nm region had been observed in Er3+:YVO4 single crystals. A magnetic field up to 5T was applied onto the sample to further tune the energy structures. Then crystal field theory models were built to analyze the crystal field induced- and magnetic field induced-energy splitting. In the models, both the coulomb potential between the ions and the magnetic Hamilton energy were considered as perturbations. Comparison between the experimental and theoretical results demonstrates that the calculations agree well with the experimental results. Furthermore, the calculation methods proposed here can also help people better understand the interactions between the ions and the fields, and open up a way to tailor the spectral output of the crystals, which is very important for design of wavelength division multiplexing optoelectronics and telecommunication devices.

Investigation of visible emission induced by infrared femtosecond pulses in erbium-doped YVO4 and LuVO4 single crystals

Illumination of single crystal samples of erbium-doped YVO4 and LuVO4 by infrared femtosecond pulses brings about an intense green luminescence assigned to the 4S3/2 - 4I15/2 transition of Er3+ ions. When lowering the sample temperature an additional broad band in the blue related to the VO43− emission appears and next grows steadily. It has been observed that the variation of wavelength of incident infrared femtosecond pulses in the region 800nm–1600nm affects weakly the intensity of both the blue and green luminescence bands. Analysis of luminescence dynamics made it possible to reveal that upon infrared excitation the rise time of the 4S3/2 luminescence is longer by a factor of four, roughly as compared to that recorded upon direct excitation into high energy levels of Er3+. Observed temperature dependence of up-converted blue and green luminescence implies that the energy transfer from vanadate groups cannot be considered as a main mechanism involved in the excitation erbium ions. It has been supposed that erbium ions are likely to be excited by energy transfer from free electrons created in the conduction band of the host by multiphoton excitation and /or by non-resonant multi-step ETU process involving absorption of infrared light in multiphonon side bands of electronic transitions. Creation of free electrons has been corroborated by changes of electrical conductivity of crystals induced by an illumination with infrared femtosecond pulses.

Absorption induced photoluminescence intensity modulation of Er3+:YVO4 single crystal under pulsed high magnetic field

A bright green photoluminescence of Er3+:YVO4 single crystal, excited by 407.6nm femtosecond laser, was investigated under pulsed magnetic field up to 47T. The integrated photoluminescence (PL) intensity is enhanced as magnetic field increases and reaches the maximum at around 4.5T, while further increasing of magnetic field up to 47T will suppress the PL intensity. And similar profile was observed in magnetic field dependent absorbance at excitation wavelength. These results are different from the reported literatures, detailed study here helps us to better understand the effect of magnetic field on Er doped materials and points out an efficient way to modulate the optical properties of luminescence materials which is important for the design and optimization of future devices.

Hyperfine structure of EPR spectra of Gd3+ odd isotopes in PbMoO4, Pb5Ge3O11, YVO4, and quadrupole interaction (temperature dependence)

A hyperfine structure of EPR signals of odd isotopes Gd3+ in Pb5Ge3O11, PbMoO4, and YVO4 single crystals has been investigated at different temperatures. The observation of forbidden (with the nuclear spin flip) transitions has made it possible to determine quadrupole interaction P20 associated with the gradient of the electric field of ligands at the impurity. It has been shown for the first time that, under the condition |P20| ≥ |Ax, y| (Ai are the tensor components), not only the magnitudes of splitting but also the observed asymmetry in a hyperfine structure (in perpendicular orientations of the magnetic field) depends on mutual signs of parameters of initial splitting b20 and P20. Results of studying the spectra have demonstrated that |b20(T)|/|P20(T)| ∼ const for a concrete single crystal, which assumes the similarity of physical mechanisms determining these parameters.

Growth and laser action of Yb: YVO4 crystals with low Yb doping concentration

Yb: YVO4 single crystals with low doping concentrations of Yb3+ less than 0.3at% were grown using the Czochralski method. The polarized absorption spectra were measured at room temperature. Strong anisotropy exists in the absorption spectra, resulting in almost entirely different features for π-polarization and σ-polarization. The laser emission spectrum and relationship curve between the output power and absorbed pump power (Pabs) were measured. The continuous-wave laser action of Yb: YVO4 single crystal in a range of 1020.4–1026.3nm was realized by using a high-power diode laser as the pump source.

Continuous wave and passively Q-switched laser performance of a composite crystal bonded with three Nd:YVO4 single crystals

The laser performance of a composite crystal bonded with three Nd:YVO4 single crystals has been investigated for the first time as far as we know. The largest continuous wave output power of 2.68 W is obtained at the incident pump power of 6.2 W, giving an optical conversion efficiency of 43.1% and a slope efficiency of 45.9%. For passively Q-switched operation with Cr4+:YAG of 71% initial transmission, the shortest pulse width of 18.2 ns, the largest single-pulse energy of 19.9 μJ, and the highest peak power of 1.12 kW are achieved, with the pulse repetition rate being 44.9 kHz, at the incident pump power of 6.2 W. The composite crystal can generate more excellent laser performance, when compared with the single crystals.

Singular ring‐shaped distribution of Nd in NdxY1‐xVO4 crystals grown by floating zone method

AbstractA singular ring‐shaped distribution of high Nd concentration was observed in Nd‐doped YVO4 single crystals grown by the floating zone (FZ) method. The ring‐shaped distribution appeared 500‐1000 μm inside from the rim of the crystals. Results of growth experiments by the anisotropic heating floating zone (AHFZ) method showed that the Nd concentration was high at the high‐temperature side of the grown crystals. We found a small concave projection at a part of the convex solid‐liquid interface by quenching the molten zone during growth. The cause of the singular ring‐shaped distribution of the Nd‐rich area was discussed in relation with the concave projection at the interface and the convection in the molten zone. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of temperature on spectroscopic features relevant to laser performance of YVO_4:Er^3+ and GdVO_4:Er^3+ crystals

Optical spectra and luminescence decay curves were measured for erbium-doped YVO(4) and GdVO(4) single crystals as a function of temperature in the 300 K-670 K temperature region. In spite of structural similarity the two systems studied display significantly different transition intensities and nonradiative relaxation rates. It was found in particular that the intensity of parasitic upconverted emission excited at 978 nm depends weakly on temperature for YVO(4):Er(3+), whereas it decreases monotonously with increasing temperature for GdVO(4):Er(3+) and becomes negligibly small at 670 K. It was concluded that GdVO(4):Er(3+) may be a promising laser active material operating at high thermal loading conditions encountered in high-power diode-pumped IR lasers.

Theoretical analysis and experimental research on thermal focal length of a YVO4/Nd:YVO4 composite crystal

This paper investigates the temperature field distribution and thermal focal length within a laser diode array (LDA) end-pumped YVO4/Nd:YVO4 rectangular composite crystal. A general expression of the temperature field distribution within the Nd:YVO4 rectangular crystal was obtained by analysing the characteristics of the Nd:YVO4 crystal and solving the Poisson equation with boundary conditions. The temperature field distributions in the Nd:YVO4 rectangular crystal for the YVO4/Nd:YVO4 composite crystal and the Nd:YVO4 single crystal are researched respectively. Calculating the thermal focal length within the Nd:YVO4 rectangular crystal was done by an analysis of the additional optical path differences (OPD) caused by heat, which was very identical with experimental results in this paper. Research results show that the maximum relative temperature on the rear face of the Nd:YVO4 crystal in the composite crystal is 150 K and the thermal focal length is 35.7 mm when the output power of the LDA is 22 W. In the same circumstances, the experimental value of the thermal focal length is 37.4 mm. So the relative error between the theoretical analysis and the experimental result is only 4.5%. With the same conditions, the thermal focal length of the Nd:YVO4 single crystal is 18.5 mm. So the relative rate of the thermal focal length between the YVO4/Nd:YVO4 crystal and the Nd:YVO4 crystal is 93%. So, the thermal stability of the output power and the beam quality of the YVO4/Nd:YVO4 laser is more advantageous than the laser with Nd:YVO4 single crystal.