Here, we show that the long-accepted mechanism for the production of red and blue emission through upconversion (UC) of 1 μm excitation in Yb(3+)/Er(3+)-doped materials does not apply in the popular β-NaYF4 host. We propose a new mechanism involving Yb(3+)-to-Er(3+) energy-transfer UC out of the green-emitting (2)H11/2,(4)S3/2 states that quantitatively accounts for all of the observed optical behavior. Rate constants for the relevant radiative and nonradiative processes are reported along with a prediction of the power dependence of the pulsed and continuous-wave UC quantum efficiency.

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A method is described for producing highly luminescent composite NIR-to-visible upconversion thin films, made from β-NaYF4:3%Er,17%Yb nanocrystals in a polymethyl methacrylate (PMMA) matrix, which require no postdeposition heat treatment. Nanocrystals are synthesized via a single-phase, high-boiling-point solvent method, which requires neither metal-trifluoroacetate precursors nor the use of autoclaves. Highly luminescent films are produced that can be varied in thickness down to dimensions approaching those of the nanocrystals themselves. The physical properties of the films are characterized by AFM and TEM, whereas the spectroscopic properties are characterized by NIR-to-visible confocal microscopy and by the time-dependence of upconversion luminescence following pulsed NIR excitation. It is shown that dispersal of β-NaYF4:3%Er,17%Yb nanocrystals in PMMA has no adverse effect on the intrinsic quantum efficiency of upconversion. By focusing the NIR pump beam (980 nm, cw) in the film, linear intensity response and constant color balance are achieved at pump powers down to 40 μW. It is also demonstrated that the thin-film method can be modified to produce large NIR-to-visible upconversion monoliths of high optical quality. This study supports an earlier assertion that the upconversion properties of β-NaYF4:Er,Yb nanocrystals approach those of the bulk material when nanocrystal size is greater than ∼70 nm.

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Alkali oxides added to methanol catalysts increase the formation of ethanol, n‐propanol and isobutyl alcohol. This result has been known for many years, yet few quantitative studies have been reported in the literature. Data obtained on a commercial copper‐zinc oxide catalyst promoted with K2 CO3 are presented and compared with published work. The optimum promoter concentration was about 0.5% by weight. The H2 to CO feed ratio was important in determining the higher alcohol selectivity. The rate of production of isobutyl alcohol varied as p H2−0.7 p CO2.2 while for methanol, ethanol and n‐propanol both exponents were positive and less than 1.6. Decreasing the hydrogen to carbon monoxide ratio from 2 to 0.5 more than doubled the isobutyl alcohol selectivity. Chain growth schemes predicting the higher alcohol selectivity are presented and estimates of the parameters are given.

Expressions are derived which predict satisfactorily the observed isomer and carbon number distribution of products from iron and cobalt catalysts in the Fischer-Tropsch synthesis. These expressions are based on three schemes of stepwise addition of one carbon atom to the end or adjacent-to-end carbons of the longest carbon chain of the growing group at the catalyst surface. The implications of these schemes to some general aspects of the reaction mechanism are considered.