Combustion synthesis technology overcame the disadvantages of high temperature solid-state reaction

and resolved the serious pollution of sulfur for the environment

what's more

phosphor powders of the small particle size were achieved

which could enhance the resolution of imaging system to some extent. X-ray phosphor powders of

Ln

2

O

2

S:

RE

3+

(where

Ln

=La

Gd;

RE

=Eu

Tb)were prepared by combustion reactions. In detail

different kinds of rare earth nitrates were weighed and mixed in stoichiometric amounts

where the doses of the dopant were 0.15%

0.35% and 0.5% in mol fraction

respectively. The nitrates were molten during drying in an oven at 100℃

and during the cooling of these mixed nitrates reactants

appropriate amounts of organic fuel

such as dithio-oxamide were added

mixed and ground along with the nitrates

where molar ratio of dithiooxamide to the rare earth nitrates was 2. The mixtures were heated in an air tube furnace with the ignition temperature of 300~350℃. To evaluate the effects of heat treatment

the combustion-prepared powders were also heated to 500~700℃ in air. The samples were characterized by X-ray diffraction (XRD)

scanning electronic microscope (SEM)

photoluminescence(PL) and X-ray excited luminescence (XEL). XRD results showed the oxide sulfide phases only when the sintering temperatures were lower than 500℃

which avoided the defect of high sintering temperature. SEM results showed a loose

porous agglomeration and a continuous three-dimensional network

and the primary particlesize is not more than 50nm. PL spectra showed the characteristic emission of rare earth activation ions

respectively. To our satisfaction

the PL intensities were nearly the same as some commercial X-ray phosphors. XEL spectra showed the same characteristic emission

although their luminescence principals were different each other. In addition

the absorption coefficients and the dopant concentration doped of these samples weren't the same for X-ray excitation

therefore

their light emission efficiencies were also different.