Synthesis, characterization, and luminescence studies of rare-earth-activated NaMgF3.

NaMgF3 -based phosphors have been described frequently in the literature. Their synthesis faces difficulties typical of fluoride materials. A simple precipitation synthesis for NaMgF3 -based phosphors is described in this paper. This consisted of mixing aq. NaF and MgCl2 /MgSO4 solutions. Various activators could be incorporated by adding the required salts during this process. Characteristic emission of the activators was observed in the prepared phosphors. As-prepared samples exhibited predominantly trivalent lanthanide emission. After thermal treatment in a reductive atmosphere, europium-doped samples showed the intense emission of Eu2+ . By virtue of the intense nature of the emission, lifetime measurements could be made for this sample. Notably, intense thermoluminescence and optically stimulated luminescence were observed in NaMgF3 :Eu. A simple, fast method for the synthesis of NaMgF3 was therefore developed.

Modification of luminescence spectra of CaF2:Eu2+.

CaF2:Eu(2+) is a well known phosphor having efficient excitation in the near ultraviolet (NUV) range. Phosphors with NUV excitation are required in newly emerging applications such as photoluminescence liquid crystal displays (PLLCD), solid-state lighting (SSL), and down-conversion for solar cells. However, emission of CaF2:Eu(2+) is around 424 nm. Eye sensitivity drops considerably at these wavelengths. It is thus not useful for display applications for which emission in one of the primary colours (blue - 450 nm, green - 540 nm or red - 610 nm) is required. Efforts were made to modify the Photoluminescence (PL) spectra of CaF2:Eu(2+) to meet these requirements using co-dopants. A Ca0.49 Sr0.50 Eu0.01 F2 phosphor showing better colour coordinates and having an emission maximum around 440 nm was discovered during these studies.

UVB emitting phosphors based on singly and co-doped Ce3+, Gd3+ in Li4ZrF8 phosphors.

Preparation of Li4ZrF8:Ce3+ and Li4ZrF8:Ce3+,Gd3+ phosphors is described. Data on luminescence characteristics are presented. Hydrothermal route was employed for the synthesis. Li4ZrF8 crystallizes in orthorhombic system with Pnma space group. Li atoms are distributed over two sites, both having same coordination of six. Zr is also similarly distributed over two 8 coordinated sites. Li4ZrF8:Ce3+ emits a broad band UVB light, while the emission of Li4ZrF8:Ce3+,Gd3+ is in form of a narrow line around 311 nm attributed to 6P7/2 â†’ 8S7/2. Both phosphors exhibited a broad excitation spectrum with a peak at 253 nm. The excitation and emission properties are thus adequate enough to obtain UVB light sources using a conventional high pressure mercury vapour lamp or an ultraviolet LED.