Growth of SrB₄O₇ Crystal Fibers with Near-Stoichiometric Composition by the Micro-Pulling-Down Method

Abstract

SrB 4 O 7 (SBO) has recently received much attention as a wavelength-conversion material which can operate into the deepest ultraviolet wavelengths (125 nm). The utilization of SBO for semiconductor lithography and laser ablation requires fully transparent crystals. Here, we show the growth of SBO crystal fibers with near-stoichiometric composition by the μ-pulling-down method. SrB 2x O 3x+1 ceramics sintered with various values of x were evaluated by X-ray diffraction (XRD). The melting point of the SBO ceramics was measured by differential scanning calorimetry (DSC) as 1017 °C, and the heat of fusion was 63.3 J/g. Furthermore, we observed SBO crystal fibers grown with various x values by optical microscopy. As a result, even when the deviation from stoichiometric composition was ± −0.1 mol % SrO (x = 2 ± 0.004), SrB 2 O 4 /SrB 6 O 10 appeared. Also, DSC curves of SBO ceramics exhibited only one melting peak. These results demonstrate that SBO shows no solid-solution width and that the stoichiometric composition is equal to the congruent composition. Furthermore, we succeeded in obtaining transparent SBO crystal fibers by growth with a stoichiometric composition. In contrast, since growth ridges including SrB 2 O 4 /SrB 6 O 10 were formed on surfaces of the SBO single crystals, SBO crystal fibers grown with nonstoichiometric composition were opaque. We could explain the formation of growth ridges via compositional supercooling on rims.

Effects of the Application of Electric Fields on the Growth of SrB4O7 Crystals by the Micro-Pulling-Down Method

“…The surface morphology without the application of electric fields was concave, as shown in our previous study (Figure 8A,B). 28 A Marangoni convection without the application of electric fields also does not occur owing to the high viscosity. On the other hand, the application of electric fields provides surface-morphological changes.…”

Growth of SrB4O7 Crystal Fibers along the c-Axis by Micro-Pulling-Down Method

“…The convection also emerges irrespective of crystal faces of growth fronts. Since it is well-known that growth by the µ-PD method does not exhibit the generation of the convection, even in the growth during the application of electric fields [21,26,31,32], the result contradicts the conventional concept of the growth by µ-PD method. In particular, the convex size became large at 75 K/mm and 1000 V/cm.…”

“…Hence, the utilization of high temperature gradients can be useful for the fabrication of twins. In addition, it is well-known that the growth by µ-PD method does not exhibit the generation of the convection even in the growth during the application of electric fields [21,26,31,32]. Many researchers strongly believe that borates, which show extremely high viscosity, grow without convection.…”

“…The µ-PD furnace used in this study was the same as in our previous studies [23][24][25][26]. Figure 1A-C show a hot zone of the µ-PD furnace.…”

Luminescence and vacuum ultraviolet excitation spectroscopy of samarium doped SrB4O7

“…Interestingly, trivalent samarium (Sm 3+ ) can constitute an emission component with high quantum efficiency arising from the emitting 4 G 5/2 4f 5 level [4,[9][10][11][12][13][14][15][16][17][18][19][20]. Overall, combining Sm( n+ ) activators in wide band gap materials can benefit the optical utilizations [21][22][23][24].…”