An analysis of infrared conversion to visible and ultraviolet radiation by Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in crystals is presented. The expression for the visible power output in the presence of back transfer from the active ion to the energy-transferring ion (Yb3+) is given and the relationship between the intermediate state transfer and back transfer coefficients for maximum output is found. If this relationship is satisfied the visible output in the presence of back transfer is equal to the maximum output with no back transfer. The behavior of the power output when the transfer and back transfer coefficients depart significantly from this optimum condition is examined and the parameters which govern the power output under these conditions are determined. The analysis is applied to Yb3+–Er3+, Yb3+–Ho3+, and Yb3+–Tm3+ ions in BaYF5 and BaY2F8. Measurements on the brightest composition of Yb3+–Er3+ ions in BaYF5 indicate that the advantage of a long-lived intermediate state is diminished by back transfer. A power-conversion efficiency of 0.1% has been obtained for the green emission from BaYF5:Yb3+–Er3+ when pumped by 0.93-μ radiation from a 17% efficient Si–GaAs diode. Conversion efficiencies of 0.03% are obtained for the green emission from BaY2F8:Yb3+–Ho3+ and for the blue emission at 4800 Å from BaYF5:Yb3+–Tm3+. Efficient conversion of 1.5-μ radiation to the visible by BaYF5:Er3+ is also described.

The stepwise conversion of infrared (=0.97 p) radiation to near infrared {0. 81 p) and visible (0.475 p) light in YF3 sensitized with Yb ' and activated with Tm ' has been studied in detail. The lifetimes and fluorescence intensities of the important manifolds (Yb I"&~2, Tm 3H4, Tm E4, and Tm G4), as we11 as the Yb-to-Tm transfer probability coefficients for the three steps of the process, have been measured as functions of concentration. A saturation effect previously observed in the Tm emission versus infrared excitation intensity has been shown to result from the rate of depopulation of Tm H4 by the second Yb-to-Tm transfer exceeding the Tm H4 decay rate. This was used to determine the second transfer probability coefficient.The first transfer probability coefficient was found to be 1.2&&10 ' cm sec independent of Tm concentration and for Yb concentration of the order of 10 at. /o and greater. The second transfer probability coefficient was found to be approximately 10 4 cm sec for Yb concentrations of 25 at. % and greater. The third transfer probability coefficient was found to be 2. 7x10 cm sec . The dependence on Yb concentration of the relative efficiency of conversion to 0.475p light agrees well with the values calculated from a rate-equation model using the measured lifetimes and transfer probability coefficients.

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The photoelectrochemical oxidation of (i00), (I 11), and (i 11) n-InP and n-GaAs in several acidic solutions has been investigated. Specific interactions between the single crystal semiconductors and solvent selectively revea_l_crystal faces other than those originally exposed to the solvent. The relative stability of the n-lnP faces is (111) > ( 100) > ( 111). The first case of electron injection during the photoanodic dissolution of III-V compound semiconductors has been observed with (I 00) and ( 111) n-InP. Nucleophilic attack by Cl-or Br-produce intermediates whose potential and kinetics allow electron injection into the semiconductor conduction band reducing the number of photons required for the reaction from six to four. The conditions for selectively etching smooth surfaces on (100) n-lnP are discussed in detail along with the conditions for maintaining polished surfaces on n-lnP(lll) or A-face, which is difficult with conventional chemical polishes.

Fundamental optical scattering and absorption mechanisms have been identified which limit light transmission in fiber optical waveguide materials. These mechanisms, which are intimately associated with the random structure in the liquid and glassy state, are described and then used as a basis for comparing fiber optical waveguide materials. It is concluded that pure fused silica is a preferred waveguide material, having ultimate total losses of 1.2 dB/km at the Nd : YAG laser wavelength of 1.06 μ, 3.0 dB/km at the GaxAl1−xAs emission wavelength of approximately 0.8 μ, and 4.8 dB/km at the GaP : Zn, O emission wavelength centered at 0.7 μ.