ABSTRACT
The paper describes synthesis and structural characterization of the whole series of two closely related lanthanide coordinated chromium or aluminum hexamolybdates (Anderson-Evans cluster) including twelve new members hitherto unreported: [Ln(H2O)7{X(OH)6Mo6O18}]·4H2O and [Ln(H2O)7{X(OH)6Mo6O18}Ln(H2O)7]{X(OH)6Mo6O18}·16H2O where X = Al or Cr and Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y. Crystal structures of all the solids were established by powder and single crystal X-ray diffraction techniques. The two series are dictated by a different aggregation of the same set of molecular species: Lighter lanthanides favor coordination interaction between lanthanide ions and molybdate cluster forming 1D chains (Series I) while the heavier lanthanides result in the stacking of a cation, a pair of lanthanide hydrates coordinating to the cluster, and an anion, the discrete cluster is further stabilized through a large number of water molecules (Series II). Crystallization with Er3+ and Tm3+ ions results in a concomitant mixture of Series I and II. Photoluminescence of single crystals of all the chromium molybdates was dominated by a ruby-like emission including those which contain optically active ions Pr, Sm, Eu, Tb, Dy, and Tm. In contrast, aluminum analogs showed photoluminescence corresponding to characteristic lanthanide emissions. Our results strongly suggest a possible energy transfer from f levels of lanthanide ions to d levels of chromium (III) causing the quenching of lanthanide emission when coordinated with chromium molybdates. Intensity measurements showed that the emission from chromium molybdates are almost two orders of magnitude lower than naturally occurring ruby with broader line widths at room temperature.
ABSTRACT
OBJECTIVE: To compare phototherapy devices based on their physical and photo-biological characteristics viz spectral properties, maximum and mean irradiance, treatable percentage of body surface area, decay of irradiance over time and in vitro photoisomerisation of bilirubin. DESIGN: In vitro experimental study. SETTING: Ocular pharmacy laboratory at a tertiary care hospital. METHODLOGY: All the characteristics were measured at a fixed distance of 35 cm from one compact fluorescent lamp (CFL) and three light emitting diode (LED) phototherapy devices in a dark room with an irradiance of <0.1uW/cm2/nm. Estimation of products of in vitro photoisomerisation was done using liquid chromatography - tandem mass spectroscopy (LC-MS/MS). RESULTS: The emission spectral data were comparable between the phototherapy devices. The devices, however, differed in their maximum irradiance with the spot and indigenous LED units having the highest and lowest values, respectively (56.5 and 16.8uW/cm2/nm). The mean irradiance measured in 5x5cm grids falling within the silhouette of a term baby of the spot and improvised LED devices were low (26.8uW/cm2/nm and 11.5uW/cm2/nm, respectively) possibly due to unevenness in the irradiance of light falling within the silhouette. There was a significant difference in the amount of bilirubin left after exposure to light over a 2hour time period (% reduction of bilirubin) among the four devices (P=0.001); at 120 minutes after exposure, the amount of bilirubin left was lowest for the CFL (16%) and spot LED (17%) devices and highest for the indigenous LED unit (41%). CONCLUSIONS: The four phototherapy devices differed markedly in their physical and photobiological characteristics. Since the efficacy of a device is dependent not only on the maximum irradiance but also on the mean irradiance, rate of decay of irradiance, and treatable surface area of the foot print of light, each phototherapy device should have these parameters verified and confirmed before being launched for widespread use.
