Doped Single Crystals Research Articles

Enhanced red and green up-conversion in Er3+-Yb3+ doped Na5Lu9F32 single crystals through Tb3+ incorporation

Er3+/Yb3+/Tb3+ tri-doped Na5Lu9F32 single crystals were prepared by a Bridgman method. The spectroscopic characteristics of the synthesized single crystals were systematically investigated. Intense green and red emissions originated from transitions for Er3+ and Tb3+ ions were observed. It was found that the introduction of Tb3+ ions to the Er3+/Yb3+ co-doped single crystals can effectively adjust the emission from near-infrared (NIR) to visible region for Er3+ ions. The emissions at 660, 522 and 542 nm from Er3+/Yb3+ co-doped single crystals were enhanced as the Tb3+ concentration increases. The energy transfer mechanisms among Er3+, Yb3+ and Tb3+ ions were also discussed. Analysis on the decay curves suggests that electric dipole-dipole is dominant for the energy transfer from Tb3+ to Er3+ ions. According to the measured lifetimes of Er3+/Yb3+ and Er3+/Yb3+/Tb3+ doped samples, the maximum energy transfer efficiency from Tb3+ to Er3+ approaches up to 11.7%. The intense green and red up-conversion observed in the Er3+/Yb3+/Tb3+ tri-doped Na5Lu9F32 single crystals make them promising candidates for solid-state multicolor displays, temperature sensors, and biomedical imaging applications.

Spectroscopic properties of Er:Lu2O3 crystal in mid-infrared emission

High optical quality Er3+ doped Lu2O3 single crystal with optimum doping concentration was grown by Floating zone (Fz) method. The spectral properties and Judd-Ofelt (JO) analysis were reported. The emission cross-section at 2772 nm was calculated to be 2.47 × 10−20 cm2 with FWHM of 188 nm. The fluorescence lifetime of 4I11/2 and 4I13/2 energy level was fitted to be 1.62 ms and 4.02 ms. Optimum lifetime ratio (τlow/τup) is beneficial to laser operation. Compared with reported Er3+ doped crystal, the larger spectral quality factors Q and low inversion ratio P of 7 at.% Er:Lu2O3 crystal indicate that it has a favorable laser performance for 2.8 μm laser operation.

Effect of lithium codopant concentration on the luminescence properties of (Lu0.75Y0.25)3Al5O12: Pr3+ single crystals: Before and after air annealing

In this paper, we present the photoluminescence and scintillation performance of Pr3+ doped (Lu0.75Y0.25)3Al5O12 single crystals as a function of Li+ concentration. Lithium concentration had no effect on the optical properties of LuYAG: Pr single crystal scintillators regardless of concentration. On the other hand, scintillation light yield increased by as much as 94% with the incorporation of lithium as a codopant, and the energy resolution at 662 keV was improved to 4.1%, which is an outstanding energy resolution for an oxide single crystal scintillator. Lithium codoping slightly lengthened the fast component of the scintillation decay time, and slightly decreased the contribution from the slow component. Additionally, the samples were annealed in air and scintillation properties were compared before and after this annealing treatment. The change in scintillation properties is explained through the analysis of thermoluminescence glow curves.

Optical properties CaWO4:Nd3+/PMMA composite layered structures

In this article, we report characterization of the layered composite fabricated from Nd3+ doped calcium tungstate single crystal (CaWO4:Nd3+) and poly(methyl methacrylate) - PMMA with various organic-inorganic interfaces: CaWO4:Nd3+/MPTMS, CaWO4:Nd3+/PMMA and CaWO4:Nd3+/MPTMS/PMMA, a novel approach to optical composite materials. A trivalent neodymium-doped CaWO4 single crystal was grown by the Czochralski method. Poly(methyl methacrylate) - PMMA, was used as a protective polymer coating and (3-mercaptopropyl)trimethoxy silane (MPTMS), with aim to provide better adhesion between the crystal surface and the polymer in the composite. The optical properties of the crystal plates with various layers applied on surface were characterized using FTIR absorption, IR reflectivity, Raman and photoluminescence spectroscopy. Performed tests on the structural, optical and photo-luminescent properties of composites can facilitate the research of potential applications in micro- and optoelectronics. Hardness of CaWO4:Nd3+ before and after surface modification was determined by micro Vickers hardness test. The improved hardness of composite with the use of the MPTMS as an adhesion primer before PMMA was achieved. FTIR spectroscopy indicates the establishing of chemical bonding between single crystal layer, silane and polymer layer. Raman and PL spectroscopy confirm that optical properties of crystal with polymer layers were preserved.

Crystal growth and 570 nm emission of Dy3+ doped CeF3 single crystal

A Dy3+-doped CeF3 yellow region laser crystal was successfully grown using the Bridgman method. A 570 nm emission in Dy:CeF3 crystal was observed for the first time. By analyzing the absorption and emission measurements of the Dy:CeF3 crystal with the Judd–Ofelt theory, the intensity parameters Ω2,4,6, exited state lifetimes, branching ratios, and emission cross-sections were calculated. It is found that the Dy:CeF3 crystal has high emission cross section (0.9259 × 10−20 cm2) and long fluorescence lifetime (1.53 ms) corresponding to the stimulated emission of Dy3+:4F9/2 → 6H13/2 transition. We propose that the Dy:CeF3 crystal may be a promising material for 570 nm laser applications.

Study of ac and dc electrical resistivity variation with high pressure of as-grown pure, indium and antimony doped SnS single crystals

The direct vapour transport technique grown single crystals of pure SnS, indium (5 and 15 at%) doped SnS and antimony (5 and 15 at%) doped SnS are used in the present study. The as-grown single crystals are completely characterized. The single crystal growth and comprehensive characterization results are presented in another research paper of the authors. All the as-grown single crystals are p-type semiconductors. The ac and dc electrical resistivity variation with high pressure of the as-grown single crystals up to 5 GPa are measured. The obtained ac and dc electrical resistivity variation with high pressure results are deliberated in this paper.

Optical activity and electro-optic effect of l-arginine doped KDP single crystals

We have used the modified polarimetric methods to study optical activity (OA) in the potassium dihydrogen phosphate (KDP) crystals doped with 0.7, 1.4 and 3.8 wt% l-arginine (l-arg) amino acid. Crystals were grown by the temperature reduction method. Small changes of the absolute eigen waves ellipticity and OA values in doped crystals were noted. We have experimentally determined the signs of OA in the [1 0 0] and [0 1 0] directions in KDP type crystals. The electro-optical parameters (half-wave voltage and electro-optical coefficients r63) in l-arg doped crystals for fixed wavelengths of 633, 532 and 405 nm remain unchanged in comparison with the pure KDP.

Influence of annealing treatment on the luminescent properties of Ta:β-Ga2O3 single crystal**Project supported by the National Natural Science Foundation of China (Grant No. 51802327) and the Science and Technology Commission of Shanghai Municipality, China (Grant No. 18511110500).

Ta5+ doped β-Ga2O3 single crystals were grown by using the optical floating zone method, and then annealed in the air and nitrogen gas at 1400 °C for 20 hours. The transmittance spectra, photoluminescence (PL), x-ray irradiation spectra, and PL decay profiles of the samples were measured at room temperature. The relevant results show that the optical transmittance of the samples annealed in the air or nitrogen gas was improved. By drawing the –hv graph, it can be seen that the band gap decreased after being annealed in the air, but increased in nitrogen gas. The PL spectra and x-ray irradiation spectra show that the luminescent intensity of the sample annealed in the air increased substantially, while decreased for the sample annealed in nitrogen. The PL decay time of the Ta:β-Ga2O3 annealed in the air increased significantly compared with that of the Ta:β-Ga2O3 sample without annealing, but the tendency after annealing in nitrogen gas was opposite.

Effect of Cu2+ ion on single crystal of nonlinear optical material (glycinium oxalate)

Single crystals of pure and Cu2+doped glycinium oxalate of dimensions 18 × 10 × 2 mm3 and 10 × 7 × 2 mm3 were grown by the solvent evaporation technique, respectively. Influences of Cu2+ ions on the crystalline quality of glycinium oxalate (GOX) crystal were studied. The grown pure and doped crystals were characterized by using powder X-ray diffraction, FT-IR, and FT-Raman techniques. UV–Vis–NIR spectra of GOX and Cu2+ doped GOX single crystals had transparency in the entire visible region with cut off wavelengths, 257 nm and 265 nm, respectively. Mechanical properties of pure and doped crystals were studied using Vicker’s micro-hardness test. The presence of transition metal ion has been confirmed by energy dispersive X-ray spectroscopy (EDAX) and EPR analyses. The g-value (2.4899) was calculated from EPR analysis. The TGA/DTA analysis was performed to find the thermal stability of samples. The dielectric behavior of pure and doped crystal have been reported from 102 to 106 Hz. The third-order NLO properties such as nonlinear absorption coefficient (β), third-order nonlinear susceptibility (χ(3)) and nonlinear refractive indices (n2) of pure and doped crystal were estimated in the order of 10−6 esu.

Effect of Nd doping on the refractive index and thermo-optic coefficient of GdVO4 single crystals

Undoped and Nd (0.2, 0.6, 0.8, 1.0, 1.2 and 1.6 at%)-doped GdVO4 single crystals have been grown by optical floating zone technique. XRD analysis reveals small lattice expansion especially along c axis on Nd doping. It has been observed that the extra-ordinary refractive index (RI) of undoped GdVO4 crystals is higher than the doped GdVO4 single crystals up to 1.0 at% Nd doping, beyond which it surpasses the value of the undoped crystal. This is due to the competing effect of lattice elongation and decrease in electron density on Nd doping. The increase in RI with Nd doping is attributed to macroscopic polarization effects. Moreover, the extra-ordinary refractive index (ne) only increases on increasing Nd concentration, whereas ordinary refractive index (no) remains unaffected within the measurement limits. The temperature-dependent RI measurements depicted a positive thermo-optic coefficient (TOC) for RI and birefringence, which is ~ 10−5/°C and is independent of doping concentration. TOC for ne is higher than no, which has been explained on the basis of anisotropic thermal expansion. An important set of relations between TOC and wavelength (532–1551 nm) has been established which is useful for estimating TOC in the temperature range of 30–150 °C.

Fluorescence Properties of Eu3+ Doped in Na5Lu9F32 Single Crystals

Eu3+ ion doped cubic Na5Lu9F32 single crystals with high quality were synthesized by a modified Bridgman method by using a high 70–90 °C/cm temperature gradient for cross solid-liquid interface. The optical spectroscopic investigations of the obtained single crystal were reported for the absorption, excitation and emission. The experimental results show that a strong red emission at 609 nm attributing to the 5D0→7F2 transition of Eu3+ doped Na5Lu9F32 single crystals can be obtained under the excitation of 394 nm light and reach the maximum when the Eu3+ doping concentration is 4mol% in present research. The local covalent is enhanced and symmetry is reduced with the increase of Eu3+ concentrations inferring from the strength parameters Ω2 and Ω4 calculated by their measured emission spectra. The CIE chromaticity coordinates of the 4mol% Eu3+ doped Na5Lu9F32 single crystals are calculated as (x=0.626, y=0.3736), which are close to the NTSC standard values for red (x=0.67, y=0.33). The experimental results reveal that the single crystal can be used as potential red phosphors under near ultraviolet (NUV) light excitation.

IR-SPECTROSCOPY AND AFM-MICROSCOPY OF THE SURFACE OF GAMMA-IRRADIATED GaS AND GaS:Yb LAYERED SINGLE CRYSTALS

For the first time, information on the surface relief of the layered GaS and doped GaS:Yb single crystals subjected to gamma-irradiation was obtained using atomic force microscopy (AFM) and Fourier-transform infrared spectroscopy (FTIR). It was found that GaS is characterized by a non-uniform distribution of irregularities with different heights and periodicities, and when doping crystals with Yb atoms, the distribution of irregularities becomes more orderly, the height and periodicity of irregularities decreases. In the FTIR spectra, changes in the reflection coefficients of the surface of GaS and GaS:Yb single crystals are observed as a function of the gamma-irradiation dose (Фγ = 30…200 krad), and on the basis of spectroscopic and microscopic changes, it was found that doped single crystals are the most radiation-resistant.

Growth and spectroscopic properties of Er:Lu2O3 crystal grown by floating zone method

Er3+ doped Lu2O3 single crystal with high optical quality was successfully grown by Floating zone (Fz) method. The spectral properties and Judd-Ofelt (JO) analysis were reported. The absorption cross section at 971 nm was 1.5 × 10–21 cm2. The emission cross-section at 1558 and 2742 nm was calculated to be 2.20 × 10–20 cm2 and 3.22 × 10–20 cm2, respectively. The fluorescence lifetime of 4I11/2 and 4I13/2 energy level was fitted to be 1.59 ms and 12.43 ms. Meanwhile, the positive gain cross-section was achieved in 1.5 μm and 2.8 μm with inversion ratio P = 0.5. The low inversion ratios indicate a great potential of Er:Lu2O3 crystal with good gain performance.

Effects of a high DC magnetic field on spin reorientation in dysprosium- yttrium iron garnets at low temperatures

In this work, magnetic properties of dysprosium doped yttrium iron garnet single crystals DyxY3-xFe5O12 (1 ≤ x ≤ 3) are studied in the 2-50 K temperature range under high D.C. magnetic fields H up to 16 T. When the sample is allowed to rotate freely on itself, critical points are observed and form a critical line of second order type which increases linearly with T in the magnetic phase diagram. This line is independent of the content x delimiting a canted phase which is issued from the low symmetry angular <uuw> phase occurring from the spontaneous spin reorientation below TSR (H = 0) = 14.62 K. In comparison with the free ion, the observed reduction at 0 K of the Dy3+ moments is also discussed.

Complex impedance, FT-Raman, and photoluminescence spectroscopic studies of pure and L-phenylalanine doped ammonium dihydrogen phosphate single crystals: the correlation with hydrogen bonding defect

Ammonium dihydrogen phosphate (ADP) is an important nonlinear optical (NLO) material used for electro-optical applications. The aromatic side chain contained dopant like L-phenylalanine causes defect in ADP. The pure and L-phenylalanine doped ADP crystals are grown using slow solvent evaporation technique at room temperature. The Powder XRD spectra suggest tetragonal crystal system and slit shifting of peak. The FT-Raman shows strong absorption peak at 922 cm−1 due to v1 group symmetry of P - OH for all grown crystals without shifting indicating the single phase nature of all the crystals. The photoluminescence study suggests the presence of defects in doped crystals compared to the pure one due to increase of Stokes shift and vibrational energy relaxation phenomena. The dielectric constant and dielectric loss have shown the usual behavior with respect to frequency and temperature. The calculated electro-optic coefficient is found to be in accordance with dielectric constant. The protonic conduction is prevailing for electric transport, and from Jonscher’s plot, the correlation barrier hopping (CBH) is confirmed. The Nyquist plot and modulus spectra of pure ADP show the presence of grain and grain boundary while the same plots for L-phenylalanine doped ADP show the presence of grain only. The stretch exponent exhibits non-Debye-type relaxation.

Crystal growth, A.C. electrical and nonlinear optical studies of pure and dl-methionine doped ammonium dihydrogen phosphate single crystals

The pure and 0.1 wt% dl-methionine doped ADP crystals are grown using slow solvent evaporation technique at room temperature. The powder XRD study shows single phase nature of both grown crystals with tetragonal structural symmetry. The UV–Vis transmittance spectroscopy shows improvement in optical transmittance, energy band, and low refractive index of doped ADP crystal compare to pure ADP crystal. The Wemple–DiDomenico single oscillator model is found to be appropriate for the refractive index dispersion below the energy band edge of ADP crystal. The Nyquist plots of pure and doped ADP crystals represent presence of grain and grain boundary. The Jonscher’s powder law is successfully applied to the conductivity phenomena in pure and doped ADP crystals. The complex modulus spectroscopy helps to discriminate the grain and grain boundary in grown crystals clearly. The Non-Debye type relaxation is observed in both crystals. The nonlinear optical properties such as second harmonic generation efficiency and third order susceptibility are improved on doping the dl-methionine in ADP crystal.

Shallow and deep trap levels in X-ray irradiated β-Ga2O3: Mg

The results of the investigation of thermostimulated luminescence (TSL) and photoconductivity (PC) of the X-ray irradiated undoped and Mg2+ doped β-Ga2O3 single crystals are presented. Three low-temperature peaks at 116 K, 147 K and 165 K are observed on the TSL glow curves of undoped crystals. The high-temperature TSL peaks at 354 K and 385 K are dominant in Mg2+ doped crystals. The correlation between doping with Mg2+ ions and the local energy levels of the intrinsic structural defects of β-Ga2O3, which are responsible for the TSL peaks and PC, is established. The nature of TSL peaks and the appropriate photoconductivity excitation bands are discussed.

Optical spectra of Eu2+ ion doped KMgF3 single crystals grown by Bridgman method

High-quality KMgF3 single crystal containing 0.5 mol% europium (Eu) was prepared by an improved Bridgman method. X-ray diffraction (XRD), photoluminescence spectra and fluorescence lifetime were measured. The results indicate the reduction of Eu3+ to Eu2+ in the KMgF3 single crystal. Under the excitation of 259 nm, 370 nm and 394 nm, the sample has two distinct emissions of Eu2+:4f7→4f7(~363 nm) and 4f65d1→4f7 (~440 nm). The substitution site for Eu ion is confirmed. The optical property investigation result shows that the Eu2+ doped KMgF3 single crystal may be used as potential laser media and related materials for optical devices.

Pr3+掺杂Na5Lu9F32单晶发光性能的优化

Pr³⁺掺杂Na₅Lu₉F₃₂单晶发光性能的优化

Photoluminescence properties of N and B codoped fluorescent 4H-SiC and 6H-SiC single crystals

In this paper, N and B codoped 4H-SiC and 6H-SiC single crystals were prepared by physical vapour transport method and their photoluminescence properties were studied. The photoluminescence spectra, dopant concentrations, Raman spectra, and transmission spectra of these obtained crystals were characterized. It is observed that the fluorescent crystals radiate a warm white light that covers a wide band spectrum from 450 nm to 750 nm when they are excited by a 325 nm laser. The doped 4H-SiC single crystal presents a higher photoluminescence intensity and larger spectral band compared to that of doped 6H-SiC single crystal under the similar growth and measurement conditions. Further analyze by doping concentration and transmission spectra indicate that the photoluminescence property is strongly influenced by the N donor and B acceptor impurity level.