Provided are a tabular alumina particle and a method for manufacturing it, wherein the particle has a major axis of 30 μm or more, a thickness of 3 μm or more, and an aspect ratio of 2 to 50 and contains molybdenum; and the method includes the steps of mixing an aluminum compound of 10% by mass or more in a form of Al.sub.2O.sub.3, a molybdenum compound of 20% by mass or more in a form of MoO.sub.3, a potassium compound of 1% by mass or more in a form of K.sub.2O, and silicon or a silicon compound of less than 1% by mass in a form of SiO.sub.2, where total amount of raw materials is assumed to be 100% by mass in forms of oxides, so as to produce a mixture and firing the resulting mixture.

Crystalline NH.sub.4Be.sub.2BO.sub.3F.sub.2 or Be.sub.2BO.sub.3F (abbreviated as BBF) has nonlinear optical effect, is not deliquescent in the air, is chemically stable. They can be used in a variety of nonlinear optical fields and will pioneer the nonlinear optical applications in the deep UV band.

Crystalline NH.sub.4Be.sub.2BO.sub.3F.sub.2 or Be.sub.2BO.sub.3F (abbreviated as BBF) has nonlinear optical effect, is not deliquescent in the air, is chemically stable. They can be used in a variety of nonlinear optical fields and will pioneer the nonlinear optical applications in the deep UV band.

Crystalline NH.sub.4Be.sub.2BO.sub.3F.sub.2 or Be.sub.2BO.sub.3F (abbreviated as BBF) has nonlinear optical effect, is not deliquescent in the air, is chemically stable. They can be used in a variety of nonlinear optical fields and will pioneer the nonlinear optical applications in the deep UV band.

Crystalline NH.sub.4Be.sub.2BO.sub.3F.sub.2 or Be.sub.2BO.sub.3F (abbreviated as BBF) has nonlinear optical effect, is not deliquescent in the air, is chemically stable. They can be used in a variety of nonlinear optical fields and will pioneer the nonlinear optical applications in the deep UV band.

A method of producing an apatite crystal includes the steps of preparing an apatite single crystal expressed by the general formula M.sup.2.sub.5(PO.sub.4).sub.3X (M.sup.2 being at least atomic element selected from the group consisting of divalent alkaline-earth metals and Eu, and X is at least one atomic selected from the group consisting of halogens); placing the apatite single crystal into a space controllable to a predetermined atmosphere; supplying water vapor into the space; and heating such that the atmosphere in the space is within a 1000 C. to 1400 C. range.

A free-standing substrate of a polycrystalline nitride of a group 13 element contains a plurality of monocrystalline particles having a particular crystal orientation in approximately a normal direction. The polycrystalline nitride of the group 13 element is composed of gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof. The free-standing substrate has a top surface and bottom surface. The free-standing substrate contains at least one of zinc and calcium. A root mean square roughness Rms at the top surface is 3.0 nm or less.

A free-standing substrate of a polycrystalline nitride of a group 13 element contains a plurality of monocrystalline particles having a particular crystal orientation in approximately a normal direction. The polycrystalline nitride of the group 13 element is composed of gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof. The free-standing substrate has a top surface and bottom surface. The free-standing substrate contains at least one of zinc and calcium. A root mean square roughness Rms at the top surface is 3.0 nm or less.

A compound strontium fluoroborate, nonlinear optical crystal of strontium fluoroborate, preparation method thereof; the chemical formula of the compound is SrB5O7F3, its molecular weight is 310.67, and it is prepared by solid-state reaction; the chemical formula of the crystal is SrB5O7F3, its molecular weight is 310.67, the crystal is of the orthorhombic series, the space group is Ccm21, and the crystal cell parameters are=10.016(6) , b=8.654(6)(4) , c=8.103(5) , Z=4, and V=702.4(8) 3. A SrB5O7F3 nonlinear optical crystal has uses in the preparation of a harmonic light output when doubling, tripling, quadrupling, quintupling, or sextupling the frequency of a 1064-nm fundamental-frequency light outputted by a Nd:YAG laser, or the generation of a deep-ultraviolet frequency doubling light output lower than 200 nm, or in the preparation of a frequency multiplier, upper or lower frequency converter, or an optical parametric oscillator.

Scintillating compounds, methods of synthesizing scintillating compounds, and applications of scintillating compounds are disclosed. The scintillating compounds can include cesium rare earth silicates. A scintillating compound can include cesium, silicon, oxygen, fluorine, and one or more of europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium and scandium. The scintillating compounds can form unit cells having the general formula Cs.sub.3RESi.sub.4O.sub.10F.sub.2 with RE including rare earth metals, lanthanides, and transition metals.