A crystal is of a non-centrosymmetric structure and belongs to the −43 m point group of the cubic crystal system. M denotes an alkaline earth metal, which can be Ba, Ca, or Sr, and RE denotes a rare earth element, which can be Y, La, Gd, or Yb. The growth method of the M.sub.3RE(PO.sub.4).sub.3 crystal comprises steps as follows: (1) polycrystalline material synthesis: MCO.sub.3, RE.sub.2O.sub.3, and phosphorous compound are used as raw materials and blended according to the stoichiometric proportions; then, the phosphorous compound is further added to be excessive; the raw materials are sintered twice to obtain the M.sub.3RE(PO.sub.4).sub.3 polycrystalline material; (2) polycrystalline material melting; (3) Czochralski crystal growth. The M.sub.3RE(PO.sub.4).sub.3 crystal prepared by the invention is a high-quality single crystal.

A crystal is of a non-centrosymmetric structure and belongs to the −43 m point group of the cubic crystal system. M denotes an alkaline earth metal, which can be Ba, Ca, or Sr, and RE denotes a rare earth element, which can be Y, La, Gd, or Yb. The growth method of the M.sub.3RE(PO.sub.4).sub.3 crystal comprises steps as follows: (1) polycrystalline material synthesis: MCO.sub.3, RE.sub.2O.sub.3, and phosphorous compound are used as raw materials and blended according to the stoichiometric proportions; then, the phosphorous compound is further added to be excessive; the raw materials are sintered twice to obtain the M.sub.3RE(PO.sub.4).sub.3 polycrystalline material; (2) polycrystalline material melting; (3) Czochralski crystal growth. The M.sub.3RE(PO.sub.4).sub.3 crystal prepared by the invention is a high-quality single crystal.

An object is to reduce variation in shape of crystals that are to be formed. Solutions containing respective raw materials are made in an environment where an oxygen concentration is lower than that in air, the solutions containing the respective raw materials are mixed in an environment where an oxygen concentration is lower than that in air to form a mixture solution, and with use of the mixture solution, a composite oxide is formed by a hydrothermal method.

A method for preparing a large-size two-dimensional layered metal thiophosphate crystal includes the following steps: 1) weighing raw materials of indium spheres, phosphorous lumps and sulfur granules according to a predetermined amount and proportion, mixing them, and using iodine as a transport agent and potassium iodide as a molten salt; 2) adding the raw materials, the iodine and the potassium iodide to a reaction vessel together, and vacuum sealing it under a certain pressure, and then subjecting it to a high-temperature reaction; 3) taking out the products after the reaction, and washing the products to remove the residual iodine and potassium iodide and obtain large-size two-dimensional layered metal thiophosphate crystals. This method is simple and highly efficient.

A method for preparing a large-size two-dimensional layered metal thiophosphate crystal includes the following steps: 1) weighing raw materials of indium spheres, phosphorous lumps and sulfur granules according to a predetermined amount and proportion, mixing them, and using iodine as a transport agent and potassium iodide as a molten salt; 2) adding the raw materials, the iodine and the potassium iodide to a reaction vessel together, and vacuum sealing it under a certain pressure, and then subjecting it to a high-temperature reaction; 3) taking out the products after the reaction, and washing the products to remove the residual iodine and potassium iodide and obtain large-size two-dimensional layered metal thiophosphate crystals. This method is simple and highly efficient.

A method for manufacturing a single crystal may be by solution growth from a seed crystal, in a unit including a tank and a growth platform having a lower plate. The method may include: fastening the seed to the lower plate; introducing a crystallization solution of density d.sub.S into the tank; treating the solution in order to render it supersaturated; bringing the seed into contact with the supersaturated solution; rotating the platform until the single crystal is obtained. Before bringing the seed into contact with the supersaturated solution, the method may include forming, in the tank, of a zone for trapping parasitic crystals of density d.sub.C by introducing, into the tank, a liquid, immiscible with the growth solution, of density d>d.sub.S and d<d.sub.c, which forms with the growth solution an interface located below the lower plate.

A method for manufacturing a single crystal may be by solution growth from a seed crystal, in a unit including a tank and a growth platform having a lower plate. The method may include: fastening the seed to the lower plate; introducing a crystallization solution of density d.sub.S into the tank; treating the solution in order to render it supersaturated; bringing the seed into contact with the supersaturated solution; rotating the platform until the single crystal is obtained. Before bringing the seed into contact with the supersaturated solution, the method may include forming, in the tank, of a zone for trapping parasitic crystals of density d.sub.C by introducing, into the tank, a liquid, immiscible with the growth solution, of density d>d.sub.S and d<d.sub.c, which forms with the growth solution an interface located below the lower plate.

A hydrothermal synthesis for LiFePO.sub.4 is provided. First, each raw material solution is prepared using a degassed water in advance, second, those solution are mixed by dripping in a fixed order, and then those materials are reacted in a hydrothermal synthesis, so that LiFePO.sub.4 is obtained in a predesigned form.

A fluorescent member includes: a wavelength converter including an incidence part on which a light of a light source is incident and an output part from which a converted light subjected to wavelength conversion as a result of excitation by an incident light is output; and a reflecting part provided in at least a portion of a surface of the wavelength converter. The wavelength converter is comprised of a material whereby a degree of scattering of the light of the light source incident via the incidence part and traveling toward the output part is smaller than in the case of a polycrystalline material.

An object is to reduce variation in shape of crystals that are to be formed. Solutions containing respective raw materials are made in an environment where an oxygen concentration is lower than that in air, the solutions containing the respective raw materials are mixed in an environment where an oxygen concentration is lower than that in air to form a mixture solution, and with use of the mixture solution, a composite oxide is formed by a hydrothermal method.