The present invention relates to metal halide colloidal nanoparticles represented by a following Chemical Formula 1 and a method for producing the same:

A.sub.3MX.sub.6  [Chemical Formula 1] wherein in the Chemical Formula 1, A is an alkali metal element, M is a rare-earth metal element, and X is a halogen element.

Lanthanide double perovskite nanocrystals are described. The nanocrystals display high energy luminescence, making them useful in a variety of light-emitting materials and devices. Methods of preparing the lanthanide double perovskite nanocrystals using a hot injection method are also described.

The present invention relates to metal halide colloidal nanoparticles represented by a following Chemical Formula 1 and a method for producing the same:
A.sub.3MX.sub.6[Chemical Formula 1] wherein in the Chemical Formula 1, A is an alkali metal element, M is a rare-earth metal element, and X is a halogen element.

A core material (102) is contained in a cylindrical container (101) (first step). The container (101) is formed from a thermoplastic cladding material. The container (101) can be formed from a heat resistant glass such as a borosilicate glass, for example. The core material (102) is a halide having a lower melting point than the cladding material. Next, the container (101) containing the core material (102) is heated using a heater (151) and stretched, thereby forming an optical fiber emitter (105) comprising a core (103) formed from a halide crystal, and a cladding (104) formed from the cladding material.