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.

A free-standing substrate of a polycrystalline nitride of a group 13 element is composed of a plurality of monocrystalline particles having a particular crystal orientation in approximately a normal direction. The free-standing substrate has a top surface and a bottom surface. The polycrystalline nitride of the group 13 element is gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof and contains zinc at a concentration of 110.sup.17 atoms/cm.sup.3 or more and 110.sup.20 atoms/cm.sup.3 or less.

A free-standing substrate of a polycrystalline nitride of a group 13 element is composed of a plurality of monocrystalline particles having a particular crystal orientation in approximately a normal direction. The free-standing substrate has a top surface and a bottom surface. The polycrystalline nitride of the group 13 element is gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof and contains zinc at a concentration of 110.sup.17 atoms/cm.sup.3 or more and 110.sup.20 atoms/cm.sup.3 or less.

A calcium metaborate birefringent crystal and a preparation method and use thereof, the crystal having a chemical formula of CaB.sub.2O.sub.4 and a molecular weight of 125.70, and belonging to the orthorhombic crystal system and space group Pbcn with unit-cell parameters a=11.60(4), b=4.28(8), c=6.21(6), and Z=4, wherein the calcium metaborate birefringent crystal is a negative biaxial crystal with a transmission range of 165-3400 nm and a birefringence between 0.09-0.36; the crystal is applicable to infrared-visible-ultraviolet-deep ultraviolet bands, and is grown by a melt method, a flux method, a Bridgman method or a heat exchange method; the crystal obtained by the method of the present invention is easy to grow and easy to process; and can be used for making polarizing beam-splitting prisms.

A calcium metaborate birefringent crystal and a preparation method and use thereof, the crystal having a chemical formula of CaB.sub.2O.sub.4 and a molecular weight of 125.70, and belonging to the orthorhombic crystal system and space group Pbcn with unit-cell parameters a=11.60(4), b=4.28(8), c=6.21(6), and Z=4, wherein the calcium metaborate birefringent crystal is a negative biaxial crystal with a transmission range of 165-3400 nm and a birefringence between 0.09-0.36; the crystal is applicable to infrared-visible-ultraviolet-deep ultraviolet bands, and is grown by a melt method, a flux method, a Bridgman method or a heat exchange method; the crystal obtained by the method of the present invention is easy to grow and easy to process; and can be used for making polarizing beam-splitting prisms.

There is provided a self-supporting polycrystalline gallium nitride substrate having excellent characteristics such as high luminous efficiency and high conversion efficiency when used for devices, such as light emitting devices and solar cells. The self-supporting polycrystalline gallium nitride substrate is composed of gallium nitride-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate, and has a top surface and a bottom surface. The crystal orientations of individual gallium nitride-based single crystal grains as determined from inverse pole figure mapping by electron backscatter diffraction (EBSD) analysis on the top surface are distributed at various tilt angles from the specific crystal orientation, in which the average tilt angle thereof is 0.1 or more and less than 1 and the cross-sectional average diameter D.sub.T of the gallium nitride-based single crystal grains at the outermost surface exposed on the top surface is 10 m or more.

There is provided a self-supporting polycrystalline gallium nitride substrate having excellent characteristics such as high luminous efficiency and high conversion efficiency when used for devices, such as light emitting devices and solar cells. The self-supporting polycrystalline gallium nitride substrate is composed of gallium nitride-based single crystal grains having a specific crystal orientation in a direction approximately normal to the substrate, and has a top surface and a bottom surface. The crystal orientations of individual gallium nitride-based single crystal grains as determined from inverse pole figure mapping by electron backscatter diffraction (EBSD) analysis on the top surface are distributed at various tilt angles from the specific crystal orientation, in which the average tilt angle thereof is 0.1 or more and less than 1 and the cross-sectional average diameter D.sub.T of the gallium nitride-based single crystal grains at the outermost surface exposed on the top surface is 10 m or more.

The seed substrate comprises a base substrate and a base layer comprising a Group III nitride semiconductor formed on the base substrate, which has a high dislocation density region and a low dislocation density region. The planar pattern of the high dislocation density region is a honeycomb pattern. A hollow exists between the base substrate and the low dislocation density region. The object layer is grown through a flux method using the seed substrate. The high dislocation density region is melted back at an initial stage of crystal growth, and thereafter, the object layer is grown on the top surface of the low dislocation density region. A cavity remains between the high dislocation density region and the object layer. The presence of the cavity and the hollow makes easy to peel the object layer from the seed substrate.

The seed substrate comprises a base substrate and a base layer comprising a Group III nitride semiconductor formed on the base substrate, which has a high dislocation density region and a low dislocation density region. The planar pattern of the high dislocation density region is a honeycomb pattern. A hollow exists between the base substrate and the low dislocation density region. The object layer is grown through a flux method using the seed substrate. The high dislocation density region is melted back at an initial stage of crystal growth, and thereafter, the object layer is grown on the top surface of the low dislocation density region. A cavity remains between the high dislocation density region and the object layer. The presence of the cavity and the hollow makes easy to peel the object layer from the seed substrate.

A compound ammonium fluoroborate, a nonlinear optical crystal of ammonium fluoroborate, and a preparation method and use thereof; the compound has the chemical formula of NH.sub.4B.sub.4O.sub.6F with a molecular weight of 176.28, and is prepared by a solid phase reaction process; the crystal has the chemical formula of NH.sub.4B.sub.4O.sub.6F with a molecular weight of 176.28, belongs to the orthorhombic system, and has a space group of Pna2.sub.1 and the following unit cell parameters: a=7.615(3) , b=11.207(4) , c=6.604(3) , Z=4, V=563.6 .sup.3. The nonlinear optical crystal can be obtained by the method of the present invention. The present invention provides uses of the nonlinear optical crystal in producing harmonic light and a deep-ultraviolet frequency-multiplied light below 200 nm; and in making a frequency multiplication generator, a frequency up or down converter or an optical parametric oscillator.