Yanru Yin

Bulk growth, structure, and characterization of the new monoclinic TbCa4O(BO3)3 crystal

Bulk TbCa4O(BO3)3 single crystals with diameter of 25 mm and length of 70 mm were successfully grown by the Czochralski (Cz) method for the first time to the best of our knowledge. The main problems of crystal growth were discussed and solved resulting in a high quality crystal. The crystalline perfection of the as-grown crystal was evaluated with full-width at half-maximum (FWHM) of the rocking curve being 35.05′′, and the optical homogeneity being 7.76 × 10−5. TbCa4O(BO3)3 crystallizes in the monoclinic space group Cm with unit cell parameters of a = 8.0715(7) A, b = 16.0000(15) A, c = 3.5454(3) A, and β = 101.2550(10)°. Several interesting phenomena of atom occupancy and structure distortion were observed and analysed. Furthermore, the hardness, density, absorption and transmission spectra were measured. The TbCOB crystal has a Mohs hardness value of 5.58, and it exhibits a high transparency ranging from 490 nm to 1500 nm.

Characterisation of interface in diffusion bonded Fe3Al/Q235 carbon steel dissimilar material

Abstract Phase structure characteristics near the interface of Fe3Al/Q235 carbon steel diffusion bonding are researched by means of X-ray diffraction and TEM. The test results indicated that an obvious diffusion transition zone was formed near the Fe3Al/Q235 carbon steel interface under the conditions: heating temperature 1050 - 1100°C, holding time 60 min and pressure 9.8 MPa. The diffusion transition zone consisted of Fe3Al and α-Fe (Al) solid solution. The microhardness near the diffusion transition zone was 480 - 540 HV(25 g). There was no brittleness phase of high hardness in the diffusion transition zone. This is favourable for increasing the toughness of a Fe3Al/Q235 diffusion joint. There was a crystal orientation relationship of (110) α-Fe(Al)//(011)Fe3Al and [001]α-Fe(Al)//[100]Fe3Al between the Fe3Al phase and the α-Fe (Al) solid solution in the diffusion transition zone.

An extended application of β-Ga2O3 single crystals to the laser field: Cr4+:β-Ga2O3 utilized as a new promising saturable absorber

Considering their easy growth and doping in bulk crystal growth, and good crystalline quality, β-Ga2O3 single crystals, a very important wide-bandgap semiconductor, are now also considered to be a promising optical crystal candidate. In this work, a Cr4+:β-Ga2O3 single crystal has been grown successfully by the edge-defined film-fed growth method. The thermal conductivity of Cr4+:β-Ga2O3 has been measured along the a* direction at room temperature obtaining 16.2 W m−1 K−1, and it was much larger than that of the usually used Cr4+-doped crystals, such as Y3Al5O12 (YAG) or YVO4. The Raman spectrum indicated that the cutoff phonon energy of the β-Ga2O3 crystal was 767.8 cm−1. A passively Q-switched nanosecond pulsed Nd:YAG laser based on a Cr4+:β-Ga2O3 saturable absorber was experimentally demonstrated for the first time to our knowledge and its mechanism is explained by first-principles calculations. By inserting the Cr4+:β-Ga2O3 crystal into the Nd:YAG laser cavity, a Q-switched laser operation was obtained with a maximum average output power of 50 mW. The corresponding pulse repetition rate, pulse width, and pulse energy were determined to be of 421.5 kHz, 235.2 ns and 0.12 μJ, respectively.

Technology and interface structure for diffusion bonding of Fe3Al/18-8 dissimilar materials

Abstract The effects of technological parameters on the interface morphology and shear strength of Fe3Al/18-8 diffusion bonded joints have been researched by means of a JXA-80 scanning electron microscope (SEM) and a digital tensile press test machine. Microstructural characteristics and fracture morphology near the Fe3Al/18-8 diffusion interface, obtained under conditions of various technological parameters, have been analysed using the SEM. The test results indicate that a diffusion bonded joint with higher shear strength (στ = 226 MPa) may be obtained with a heating temperature T = 1020 – 1040°C, holding time t = 45 – 60 min and pressure P = 12 – 15 MPa.

One-step exfoliation of ultra-smooth β-Ga2O3 wafers from bulk crystal for photodetectors

High-quality bulk β-Ga2O3 single crystals have been grown by optimized edge-defined film-fed growth (EFG) method. The problems of cracking and polycrystals have been effectively solved by using a high-quality 1 inch-wide seed. The crystalline quality of the as-grown crystal has been confirmed by X-ray rocking curve with a full-width at half-maximum (FWHM) of 42.1 arcsec. Moreover, an economical and efficient one-step mechanical exfoliation method has been proposed to get epi-ready β-Ga2O3 wafers directly. The root mean square (RMS) roughness of the wafers is noted to be around 0.1 nm, which means they are comparable or even better than wafers processed by chemical mechanical polishing (CMP). The mechanism of the exfoliation method is analyzed from a crystallographic view. A photodetector is fabricated on the exfoliated wafer directly and the device is proved to show good performance in solar-blind band.

Diode End Pumped Continuous Wave and Graphene Q-Switched Tm:LGGG Lasers

A detailed investigation was conducted on continuous wave, wavelength tunable, and graphene passively Q-switched (PQS) lasers of Tm:LGGG crystal. In continuous wave operation, a maximum average output power of 2.26 W at 2003 nm was obtained under the absorbed power of 12.1 W, giving an optical-to-optical conversion efficiency of 18.7% and a slope efficiency of 23.6%. By using a quartz plate, the emission spectrum could be tuned from 1907.5 to 2055.9 nm, corresponding to a full-width at half-maximum (FWHM) of 83 nm. Dual-wavelength operation could be obtained by rotating the quartz plate at an appropriate angle. In graphene PQS regime, the Tm:LGGG laser produced a 1.29-μs pulse under the pulse repetition frequency of 43.9 kHz, corresponding to a pulse energy of 3.19 μJ.

Effect of heat treatment on microstructure near diffusion bonding interface of Fe3Al/18-8 stainless steel

Abstract The microstructure of Fe3Al/18-8 diffusion bonding joint after heat treatment was analysed by metalloscopy, scanning electron microscopy and X-ray diffraction. The experimental results indicated that the size of grains near the Fe3Al/18-8 diffusion interface was decreased significantly and the microstructure near the interface became homogeneous. The precipitations also became tiny with regular shape and were distributed evenly at the interface region. The microhardness of the Fe3A1/18-8 diffusion bonding joint was decreased and no brittle phase with high microhardness existed near the interface after heat treatment. The suitable parameters of heat treatment were: heating temperature T=800°C, holding time t=30 min, furnace cooling to 700°C then air cooling.

Charge compensations of Eu2+ and Oi2− co-exist in Eu3+:CaMoO4 single-crystal fibers grown by the micro-pulling-down method

Eu3+-Doped CaMoO4 single-crystal fibers with concentrations from 0.01 to 1 at% have been grown by the micro-pulling-down method in an air atmosphere. The origin of the coloration of the crystals can be attributed to the charge compensations. In the air or H2 annealing process, the absorption spectra combined with XPS proved the coexistence of Eu2+ and interstitial O (Oi2−). The density functional theory was simulated to display the absorption spectra of Eu2+-doped and (Eu2+–Oi2−) co-doped CaMoO4, consistent with the experimental data. The low-temperature polarized absorption and emission spectra illustrated the charge compensations. The luminescence spectra of the Eu3+ probe were used to study the Oi2− species. Luminescence decay curves of 5D0 were measured. To the best of our knowledge, this is the first report on the growth and charge compensations of Eu3+:CaMoO4 single-crystal fibers grown by the micro-pulling-down method and the reduction phenomenon of Eu3+ to Eu2+ in an oxidizing atmosphere at high temperature in molybdates. On excitation by near ultraviolet or blue light, the molybdates could be potential hosts for white-light-emitting diodes.

Yb:GGG Thin-Disk Oscillator with High Power Continuous Wave Operation

We present a Yb:GGG thin-disk laser for the first time. We demonstrate more than 50 W of output power in multimode operation at 67% slope efficiency, which is similar to values achieved with Yb:YAG.