Various morphologies of magnesium carbonate hydrates have been synthesized by carefully adjusting the reaction temperature and pH value of the initial reaction solution in the precipitation process. At lower temperatures (from room temperature to 328 K) and lower pH values (variation with the reaction temperature), magnesium carbonate hydrates are prone to display needlelike morphology, and the axis diameter of the particles decreases with the increase of reaction temperature and pH value. With the further increase of the reaction temperature (333-368 K) and pH value, the sheetlike crystallites become the preferred morphology, and at higher temperatures and pH values, these crystallites tend to assemble into layerlike structures with diverse morphologies, such as spherical-like particles with rosette-like structure and cakelike particles built from sheetlike structure. Fourier transform infrared (FT-IR) spectra show that these various morphologies are closely related to their compositions. The needlelike magnesium carbonate hydrate has a formula of MgCO3.xH2O, in which the value x is greatly affected by the experimental conditions, whereas with the morphological transformation from needlelike to sheetlike structure, their corresponding compositions also change from MgCO3.xH2O to Mg5(CO3)4(OH)2.4H2O in the interval of 328-333 K.

A novel white-light-emitting phosphor Ca(9)Lu(PO(4))(7):Eu(2+),Mn(2+) has been prepared by solid-state reaction. The photoluminescence properties indicate that there is an efficient energy transfer from the Eu(2+) to Mn(2+) ions via a dipole-quadrupole reaction. The obtained phosphor exhibits a strong excitation band between 250 and 430 nm, matching well with the dominant emission band of a UV light-emitting-diode (LED) chip. Upon excitation of UV light, white light is realized by combining a broad blue-green emission band at 480 nm and a red emission band at 645 nm attributed to the Eu(2+) and Mn(2+) ions. The energy-transfer efficiency and critical distance were also calculated. Furthermore, the phosphors can generate lights from blue-green through white and eventually to red by properly tuning the relative ratio of the Eu(2+) to Mn(2+) ions through the principle of energy transfer. Preliminary studies showed that the phosphor might be promising as a single-phased white-light-emitting phosphor for a UV white-light LED.