Provided are a liquid dispersion of fluoride particles, which has low viscosity and excellent dispersibility, and is suitable for producing an optical film such as an antireflection film; a method for producing the same; and an optical film using the same. The liquid dispersion of fluoride particles according to the present invention is that in which particles of a fluoride represented by the chemical formula A.sub.xCF.sub.y (wherein A represents sodium or potassium, C represents silicon or boron, x is 1 or 2, and y is 4 or 6) are dispersed in an aprotic organic solvent having a relative permittivity of 5 to 40, and the optical film according to the present invention is produced by using the liquid dispersion of fluoride particles.

Provided is a method for producing a fluoride phosphor. The method includes: providing a first solution containing an element M.sup.1 containing at least one selected from the group consisting of group 13 elements, manganese, and fluorine, a second solution containing an element M.sup.2 containing at least one selected from the group consisting of group 4 elements and group 14 elements, and a third solution containing at least one selected from the group consisting of alkali metal elements; and adding the second solution and the third solution to the first solution at substantially the same time.

A method for producing a fluoride fluorescent material comprises: preparing fluoride particles having a composition containing at least one element or ion A selected from the group consisting of alkaline metal elements and NH.sub.4.sup.+, at least one element M selected from the group consisting of Group-4 elements and Group-14 elements, Mn.sup.4+, and F, in which a molar ratio of A in 1 mol of the composition is 2, a total molar ratio of M and Mn.sup.4+ is 1, a molar ratio of Mn.sup.4+ is in a range of more than 0 and less than 0.2, and a molar ratio of F is 6; subjecting the fluoride particles to a first heat treatment at a temperature of 500° C. or more in an inert gas atmosphere; washing the first heat-treated fluoride particles with a washing liquid; and bringing the washed fluoride particles into contact with a fluorine-containing substance and subjecting the resulting fluoride particles to a second heat treatment at a temperature of 400° C. or more.

A method for producing a fluoride fluorescent material comprises: preparing fluoride particles having a composition containing at least one element or ion A selected from the group consisting of alkaline metal elements and NH.sub.4.sup.+, at least one element M selected from the group consisting of Group-4 elements and Group-14 elements, Mn.sup.4+, and F, in which a molar ratio of A in 1 mol of the composition is 2, a total molar ratio of M and Mn.sup.4+ is 1, a molar ratio of Mn.sup.4+ is in a range of more than 0 and less than 0.2, and a molar ratio of F is 6; subjecting the fluoride particles to a first heat treatment at a temperature of 500° C. or more in an inert gas atmosphere; washing the first heat-treated fluoride particles with a washing liquid; and bringing the washed fluoride particles into contact with a fluorine-containing substance and subjecting the resulting fluoride particles to a second heat treatment at a temperature of 400° C. or more.

A process for reducing the concentration of one or more arsenic-containing compounds in an aqueous solution comprising at least one fluoroacid, which process comprises: (i) contacting the aqueous solution with an oxidising agent to produce one or more Asv-containing compounds; and (ii) removal of precipitated arsenic-containing compounds; wherein the process comprises a step (iii) the addition of an aqueous alkali solution or slurry, which may take place after step (i) and before step (ii) or after step (ii).

Provided is a backlight unit including a light source, an encapsulation layer, and a green quantum dot film. The light source emits a blue light. The encapsulation layer encapsulates the light source. The encapsulation layer includes red phosphors and yellow phosphors. The green quantum dot film is disposed above the light source and the encapsulation layer. The blue light is transmitted through the encapsulation layer and the green quantum dot film to generate a white light. A display device including the said backlight unit is also provided.

A red phosphor that has optical characteristics and durability under high-temperature and high-humidity environments, and a method for producing the same. The red phosphor includes a Mn-activated complex fluoride represented by the following general formula (1) and bismuth:

A2MF6:Mn4+  (1)

wherein A represents at least one alkali metal element selected from the group consisting of lithium, sodium, potassium, rubidium and cesium, and M represents at least one tetravalent element selected from the group consisting of silicon, germanium, tin, titanium, zirconium and hafnium.

Provided is a fluoride fluorescent material having high luminance. The fluoride fluorescent material has a composition containing Mn, A that is at least one element or ion selected from the group consisting of alkali metal elements and NH.sub.4.sub.+, at least one element M selected from the group consisting of Group-4 elements and Group-14 elements, and F; and contains spherical fluoride particles.

The present disclosure provides a phosphor having an empirical formula Li.sub.2SiF.sub.6:Mn.sup.4+, a conversion LED including the phosphor, and a method of making the phosphor by solid-state synthesis.

Provided is a fluoride fluorescent material having high luminance.

The fluoride fluorescent material has a composition containing Mn, A that is at least one element or ion selected from the group consisting of alkali metal elements and NH.sub.4.sub.+, at least one element M selected from the group consisting of Group-4 elements and Group-14 elements, and F; and contains spherical fluoride particles.