Visible light emission has been obtained at room temperature by photoluminescence ͑PL͒ and electroluminescence ͑EL͒ from Eu-doped GaN thin films. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources ͑for Ga and Eu͒ and a plasma source for N 2. X-ray diffraction shows the GaN:Eu to be a wurtzitic single crystal film. Above GaN band gap photoexcitation with a He-Cd laser at 325 nm resulted in strong red emission. Observed Eu 3ϩ PL transitions consist of a dominant narrow red line at 621 nm and several weaker emission lines were found within the green through red ͑543 to 663 nm͒ range. Below band gap PL by Ar laser pumping at 488 nm also resulted in red emission, but with an order of magnitude lower intensity. EL was obtained through use of transparent indium-tin-oxide contacts to the GaN:Eu film. Intense red emission is observed in EL operation, with a spectrum similar to that seen in PL. The dominant red line observed in PL and EL has been identified as the Eu 3ϩ 4 f shell transition from the 5 D 0 to the 7 F 2 state.

Growth and morphology of Er-doped GaN on sapphire and hydride vapor phase epitaxy substrates

Blue emission has been obtained at room temperature from Tm-doped GaN electroluminescent devices. The GaN was grown by molecular beam epitaxy on Si(111) substrates using solid sources (for Ga and Tm) and a plasma source for N2. Indium–tin–oxide was deposited on the GaN layer and patterned to provide both the bias (small area) and ground (large area) transparent electrodes. Strong blue light emission under the bias electrode was observable with the naked eye at room temperature. The visible emission spectrum consists of a main contribution in the blue region at 477 nm corresponding to the Tm transition from the G41 to the H63 ground state. A strong near-infrared peak was also observed at 802 nm. The relative blue emission efficiency was found to increase linearly with bias voltage and current beyond certain turn-on levels.

Soaps of the type CFa(CH2),COONa have been prepared with n = 8, 10, and 11. In aqueous solution each soap produces a single, concentration-dependent fluorine magnetic resonance signal. The data readily yield values of the critical micelle concentrations and of the chemical shifts of both the monomeric soap ions and the micellar material. As judged by the cmc values these soaps are essentially similar in their behavior to the ordinary alkyl carboxylates. Comparison of the micelle shifts with shifts observed for the soaps and for CF3(CH2)sCF3 in various solvents shows that the medium surrounding the CFa group when it is in the micelle has characteristics about midway between those of water and of hydrocarbon. This suggests that there is considerable penetration of water into the interior of the micelles, a conclusion also supported by determinations of the fluorine chemical shift of solubilized benzotrifluoride. The micelle shift is virtually unaffected by changes in the size of the micelles brought about either by changing the chain length of the soap or by adding simple electrolytes.( I ) Preliminary results of this work were presented at the 151st (19641, have reported small concentration-dependent changes in the position of the water nmr signal in some detergent solutions.

Visible light electroluminescence (EL) has been obtained from Er-doped GaN Schottky barrier diodes. The GaN was grown by molecular beam epitaxy on Si substrates using solid sources (for Ga, and Er) and a plasma source for N2. Al was utilized for both the Schottky (small-area) and ground (large-area) electrodes. Strong green light emission was observed under reverse bias, with weaker emission present under forward bias. The emission spectrum consists of two narrow green lines at 537 and 558 nm and minor peaks at 413 and at 666/672 nm. The green emission lines have been identified as Er transitions from the H11/22 and S3/24 levels to the I15/24 ground state and the blue and red peaks as the H9/22 and F9/24 Er transitions to the same ground state. The reverse bias EL intensity was found to increase linearly with bias current.