The LaF nanocrystals through a facile hydrothermal route with hexagonal structures have been synthesized via doping of trivalent rare earth (RE ) ions - RE = Tb, Sm, Dy and Tm - with rod-like and perforated morphologies using NH F as fluorine precursor. Hexagonal phase formation was confirmed by powder X-ray diffraction. The crystalline sizes were calculated by the Scherrer equation where found to have an average crystalline size of 12 to 35 nm. The morphological studies of the nanocrystals were carried out by means of transmission electron microscopy (TEM). The LaF :Tm ,Sm ions show the characteristic emission of Tb and Tm respectively. In Sm -doped LaF , three prominent emission peaks at 561, 597 and 641 nm were found, which belong to G → H , G → H (magnetic dipole) and G → H (electric dipole) transitions, respectively. The Dy activated LaF shows blue and yellow emission and the corresponding CIE color coordinate show white light emission (CCT value 10650 K).

Phosphor materials are an integral and important part in the white light generation in LEDs and have participated in the global warming reduction significantly. In this chapter, the authors focus on different types of phosphor materials belonging to a family of apatites, fluoroapatites, silicates, oxides, phosphates, and borates with different crystal structures. The detailed investigations on their crystal chemical structure, synthesis, and photoluminescence properties are briefly discussed. The improved optical properties make the phosphor potential candidate for smart panel displays and white light emitting diodes (including solid state lighting). The crystal structure has a great influence on the chemical and luminescence properties of any phosphor; hence, a great change of activator ion (Eu2+, Ce3+, Mn2+, and Tb3+) concentrations can be achieved in the phosphor performances. The chapter correlates the structure-compositions-property of the phosphor materials with special emphasis on white LEDs.