Mingjun Xia

Thermo-physical properties of nonlinear optical crystal K3B6O10Br

The thermo-physical properties of the nonlinear optical (NLO) crystal K3B6O10Br (KBB) were experimentally investigated, including specific heat, thermal conductivity, coefficient of thermal expansion and refractive index. The specific heat of KBB is lower than that of LiB3O5 and higher than that of other borate NLO crystals, such as β-BaB2O4, CsLiB6O10 and CsB3O5, and KBB manifests a high damage threshold because of its lower temperature gradient during laser pulse irradiation. The thermal expansion coefficients were obtained as αx = 5.09 × 10−6 K−1 and αz = 2.39 × 10−5 K−1, showing weaker anisotropy than those of commonly used NLO crystals. The temperature-dependent Sellmeier dispersion equations of the refractive indices were also obtained, and the phase-matching angles for second harmonic generation (SHG) at temperatures of 313, 343, 373, 403 and 433 K which were calculated from these equations are in good agreement with the experimental values. All results are indicative of the KBB crystal as a novel promising NLO crystal for high power SHG.

Be2BO3F: A Phase of Beryllium Fluoride Borate Derived from KBe2BO3F2 with Short UV Absorption Edge.

A phase of beryllium fluoride borate Be2BO3F (BBF) was successfully developed and grown by spontaneous nucleation from high temperature solution. The crystal belongs to the trigonal space group of R3̅c (No. 167), with lattice parameters a = 4.442(1) Å, c = 24.956(5) Å, and Z = 2. It is constructed by the infinite planar [Be2BO3F2]∞ layers, in which the planar triangle [BO3](3-) and the tetrahedral [BeO3F](5-) anionic groups are arranged in parallel via corner-sharing O atoms in each ab plane. BBF is an incongruent compound and decomposes at about 650 °C. The deep-ultraviolet (DUV) transmittance spectrum reveals that its UV cutoff wavelength is down to ∼150 nm. Theoretical calculations show that BBF has a large birefringence (Δn = 0.13 at 200 nm), which mainly originates from the infinite planar [Be2BO3F2]∞ layers. In conclusion, BBF may be served as a potential DUV birefringent material.

High average power third harmonic generation at 355 nm with K 3 B 6 O 10 Br crystal

We demonstrate a nanosecond 355 nm laser by third harmonic generation of an Nd: YAG laser with a 4 × 4 × 13.3 mm3 type I cut K3B6O10Br crystal for the first time. The maximum average power of 19.3 W is achieved with the corresponding conversion efficiency of 16.3% and the maximum conversion efficiency of 18.3% is recorded when the 355 nm average power is 15.8W. In addition, several nonlinear optical parameters including the angle and temperature bandwidths at third harmonic generation are also investigated.

Ba5Zn4(BO3)6: A Nonlinear-Optical Material with Reinforced Interlayer Connections and Large Second-Harmonic-Generation Response

A nonlinear-optical crystal Ba5Zn4(BO3)6 (BZBO) is obtained that is constructed with [Zn4(BO3)4O6]∞ units bridged by planar BO3 groups along the a axis based on the flexibility of the BO3 and ZnO4 groups. The distance between adjacent [Zn4(BO3)4O6]∞ layers in BZBO is 5.07 Å, which is much shorter than those of KBe2BO3F2, Ba2Zn(BO3)2, and Na2CsBe6B5O15. The smaller interlayer spacing and stronger bond between neighboring layers of BZBO contribute to a better growth habit than those of the other three. Also, with the cooperation of two kinds of nonlinear-optical active groups, BO3 and ZnO4, BZBO exhibits a large second-harmonic-generation response of about 2.6 times that of KDP.

A terbium rich orthoborate LiSrTb2(BO3)3 and its analogues

A terbium rich orthoborate, LiSrTb2(BO3)3, has been successfully synthesized by a solid state reaction and crystallized from a high temperature flux. Single crystal X-ray diffraction results show that LiSrTb2(BO3)3 possesses the Pm1 space group, with cell parameters of a = 10.3845(4) A, c = 6.4739(8) A, and Z = 3. In the structure, the terbium atom coordinates to eight oxygen atoms to yield a TbO8 polyhedron. These polyhedra are connected with each other to form a layer of trigonal [Tb3O21] and hexagonal [Tb6O33] blocks in the ab plane, and then the layers are further linked by the triangular BO3 groups along the c direction. The magnetic susceptibility measurements show that LiSrTb2(BO3)3 exhibits paramagnetic behaviors from 2 K to 300 K. The diffuse optical reflection spectrum indicates that LiSrTb2(BO3)3 is transparent in the range 500–1500 nm, and effective green emission is detected in the photoluminescence of LiSrTb2(BO3)3. In addition, a series of isostructural lanthanide analogues LiSrLn2(BO3)3 (Ln = Pr, Nd, Sm–Lu) and LiBaLn2(BO3)3 (Ln = Pr, Nd, Sm–Tm) have also been prepared by solid state reactions.

LiSr3Be3B3O9F4: a new ultraviolet nonlinear optical crystal for fourth-harmonic generation of Nd:YAG lasers

A new ultraviolet nonlinear optical crystal, LiSr3Be3B3O9F4 (LSBBF), was obtained by the flux method. LSBBF is isostructural to NaSr3Be3B3O9F4 and inherits its brilliant [Be3B3O12F]10− structural units. It exhibits a considerable second-harmonic generation (SHG) intensity (∼2.2 × KDP) and short ultraviolet cut-off wavelength (∼175 nm). Further theoretical calculations revealed that the shortest SHG phase-matching wavelength of LSBBF is down to ∼245 nm. These results indicated that LSBBF has potential to be used for the 266 nm output of the fourth harmonic of Nd:YAG lasers.

Orthoborates LiCdRE5(BO3)6 (RE = Sm–Lu and Y) with Rare-Earth Ions on a Triangular Lattice: Synthesis, Crystal Structure, and Optical and Magnetic Properties

Single crystals of LiCdY5(BO3)6 were successfully grown from a Li2O-B2O3 flux, and its lanthanide homotypic compounds, LiCdRE5(BO3)6 (RE = Sm-Lu), have been prepared by solid-state reaction. They crystallize in the noncentrosymmetric space group P6522 with cell parameters in the ranges of a = 7.0989(2)-6.9337(1) Å and c = 25.9375(1)-24.8960(6) Å. As a representative example, LiCdY5(BO3)6 features a triangular lattice in the ab plane composed of three distinct crystallographic Y sites. The triangular lattices spaced with the same distance of [Formula: see text]c are further stacked to build three-dimensional frameworks by reinforcement of the isolated planar BO3 groups and distorted LiO4 tetrahedra. Magnetic measurements show that Eu and Sm compounds exhibit typical Van Vleck-type paramagnetism and other rare-earth borates show weak antiferromagnetic behavior. In addition, UV-vis-near-IR diffuse-reflectance and photoluminescence spectra were performed to understand the transition energy levels of active rare-earth ions and their relationships to magnetism.

Deep-Ultraviolet Nonlinear Optical Crystal Cs2Al2(B3O6)2O: A Benign Member of the Sr2Be2(BO3)2O Family with [Al2(B3O6)2O]2− Double Layers

For the explorations of deep ultraviolet (DUV) nonlinear optical (NLO) borates, a type of important optoelectronic material, the (BO3 )3- group has been long regarded as the sole microscopic optically-active unit, and toxic Be-containing raw materials are frequently-adopted. Herein, a new DUV NLO crystal, Cs2 Al2 (B3 O6 )2 O (CABO), was designed and synthesized by simultaneously replacing the (BO3 )3- groups and Be2+ cations for (B3 O6 )3- units and Al3+ cations in Sr2 Be2 (BO3 )2 O, which possesses a favorable structure, through a chemical co-substitution approach. CABO exhibits a considerable DUV NLO capability because of the wide band gap and large birefringence originating from the [Al2 (B3 O6 )2 O]2- double layers. Remarkably, CABO melts congruently and does not contain the toxic beryllium, which is favorable for bulk-size crystal growth and practical applications.

Photoluminescence properties and preferable site occupancy of Ce3+ in apatite-like RbSr4(BO3)3 blue-emitting phosphors for white LEDs

A near-ultraviolet (n-UV) pumped blue-emitting apatite-like phosphor RbSr4(BO3)3:Ce3+ (RSBO:Ce3+) was synthesized using a high temperature solid-state reaction method. Rietveld refinement on the structure indicates that Ce3+ ions are apt to occupy the Sr12+ (8c) site, in spite of one Rb+ and three different crystallographic Sr2+ ions in the structure. The Ce3+ ion activated RbSr4(BO3)3 (RSBO) material can be excited by a relatively broad absorption band ranging from 320 to 365 nm, which matches well with the light from the commercial n-UV white light emitting diode (w-LED) chips, and generates a strong blue emission spectrum peaking at 415 nm due to the electronic transitions from 5d to 4f of the Ce3+ ion. And the color purity of RSBO:Ce3+ is comparable to that of the blue-emitting commercial phosphor BAM:Eu2+. The temperature-dependent spectra show that its luminescence intensity at 100 °C can remain about 85% of the initial value at room temperature. A w-LED device was fabricated by combining the RSBO:Ce3+, commercial (Sr,Ba)2SiO4:Eu2+ and (Ca,Sr)SiAlN3:Eu2+ phosphors with a 365 nm n-UV chip. The w-LED device generates white light with CIE chromaticity coordinates, correlated color temperature (CCT) and color-rendering index Ra are (x, y) = (0.3315, 0.3402), 5540 K and 72.9, respectively. The experimental results indicate that the RSBO:Ce3+ phosphor is a promising candidate as a blue component for application in w-LEDs.

Chemical engineering of mixed halide hexaborates as nonlinear optical materials

Mixed nonlinear optical (NLO) crystals have been widely investigated to precisely optimize their optical properties by controlling the compositions, and have drawn immense attention in the laser science and technology field. Herein, a series of mixed NLO crystals K3B6O10Br1−xClx (x = 0, 0.21, 0.35, 0.47, 0.57, 0.75 and 1) were obtained using spontaneous nucleation and a bulk crystal of K3B6O10Br0.53Cl0.47 with the size 41 × 26 × 15 mm3 was successfully grown by a top seeded solution growth (TSSG) method. The NLO properties of the mixed crystals were studied by combination of second harmonic generation (SHG) tests and first-principles calculations. As a potential mixed crystal for practical application, the optical properties of the K3B6O10Br0.53Cl0.47 crystal including transparency range, refractive indices, the shortest SHG phase-matching wavelength and angle were investigated. The results indicate that the optical performance of the mixed crystals can be effectively adjusted to optimize practical high power laser output by tuning substitution compositions.