Abstract: Disclosed is an optoelectronic device including a lanthanum-based active layer and a method for fabricating the same. The optoelectronic device includes an active layer of multiple quantum well (MQW) structure including each well between walls, wherein the wall is a dielectric layer selected from alkali metal halide, alkali earth metal halide, alkali metal chalcogenide and alkali earth metal chalcogenide, and the well is a layer including semiconductor selected from lanthanum-based metal halide, lanthanum-based metal chalcogenide, transition metal (including post transition metal) halide and transition metal chalcogenide. The optoelectronic device including the active layer can be used in applications of LEDs, displays, optical sensors and solar cells. When the active layer is used as a photoconversion layer, displays can be implemented by upconversion or downconversion of short wavelength of UV, blue and IR light source to visible wavelength of red, green and blue.