Visible to infrared low temperature photoluminescence of rare earth doped bismuth germanate crystals.
In this paper, the influence of a series of rare earth (Eu, Tm, Nd) and Cr ion doping on the optical properties of BGO was investigated by means of photoluminescence (PL) from visible to IR region in the 10-300K temperature range using different types of detectors, namely, photomultiplier tube (PMT), InGaAs (IGA), and Si. Several samples were investigated having dopants concentrations of 0.3wt%Nd, 0.4wt%Tm, 0.06wt% Cr and 3ppm Eu. The PL spectra of the samples showed different luminescence behaviour which is assigned to the 4f intra shell transition from rare earth ions. The temperature dependence of the PL from rare earth doped BGO crystals is also examined.
An Intense Green/Yellow Dual-Chromatic Calcium Chlorosilicate Phosphor Ca3SiO4Cl2 : Eu2 + –Mn2 + for Yellow and White LED
A series of intense green/yellow phosphors Ca 3 SiO 4 Cl 2 :Eu 2+ , Mn 2+ was synthesized by a high-temperature solid-state reaction. Their luminescent properties were characterized by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetime and temperature-dependent emission spectra in the temperature range of 10-450 K. The phosphors Ca 3 SiO 4 Cl 2 :Eu 2+ , Mn 2+ show intense broad absorption bands between 250 and 450 nm, matching well with the near-ultraviolet (380-420 nm) emission band of InGaN-based chips, and exhibit two dominating bands situated at 512 and 570 nm, ascribed to the allowed 5d → 4f transition of the Eu 2+ ion and the 4 T 1g ( 4 G) → 6 A 1g ( 6 S) transition of the Mn 2+ ion, respectively. The lifetime of the Eu 2+ ion decreases with increasing the concentration of the Mn 2+ ion, strongly supporting an efficient energy transfer from Eu 2+ to Mn 2+ . By combining with near-ultraviolet (∼395 nm) InGaN chips, intense yellow light-emitting diodes (LEDs) with a much lower ultraviolet light leakage were successfully fabricated based on the Ca 3 SiO 4 Cl 2 :Eu 2+ , Mn 2+ phosphor, and intense white LEDs were made based on a blend of blue chlorophosphate phosphor and the green/yellow phosphor Ca 3 SiO 4 Cl 2 :Eu 2+ , Mn 2+ . The color coordinate, correlated color temperature T c , general color-rendering index R a , and luminous efficiency of the fabricated white LEDs are (0.3281, 0.3071), 6065 K, 84.5, and 11 lm/W, respectively.
Brauer groups of genus zero extensions of number fields
We determine the isomorphism class of the Brauer groups of certain nonrational genus zero extensions of number fields. In particular, for all genus zero extensions E of the rational numbers Q that are split by Q(√2), Br(E) ≅ Br(Q(t)).