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Visible green and red upconversion (UC) emissions with anomalous power dependence were observed in Gd2O3:Er3+ nanocrystals at room temperature under diode laser excitation of 970 nm. The green and red UC radiations both yield an “s”-shape power dependence, in marked contrast to the quadratic ones of the bulk counterparts. A closed positive looping UC mechanism that differs from conventional PA mechanism is proposed to explain the observed five- or six-photon processes in the “s”-shape power dependence. Power dependence analysis of the 1.55 μm emissions from the 4I13/2 state experimentally demonstrates our proposed model. [ABSTRACT FROM AUTHOR]

Visible green and red upconversion (UC) emissions with anomalous power dependence observed in [Gd.sub.2][O.sub.3:[Er.sup.3+] nanocrystals at room temperature under diode laser excitation of 970 nm are described. A closed positive looping UC mechanism that differs from conventional PA mechanism which explain the observed five- or six-photon processes in the s-shape power dependence are also demonstrated.

We report on an innovative route to increase the upconversion (UC) green radiation by two orders of magnitude in Y2O3:Er3+ nanocrystals through tailoring Er3+ ions’ local environment with Li+ ions under diode laser excitation of 970 nm. Theoretical investigations based on the steady-state rate equations indicate that such enhancement arises from a combining effect of the tailored lifetime of the intermediate 4I11/2(Er) state, the suppressed cross relaxation 2H11/2(Er)+4I15/2(Er)→4I9/2(Er)+4I13/2(Er) process, and the enlarged nanocrystal size induced by the Li+ ions. The proposed route here may constitute a promising step to solve the low efficiency problem in UC materials. [ABSTRACT FROM AUTHOR]

Room temperature bright white upconversion (UC) luminescence in Yb3+–Tm3+–Er3+ ions doped Y2O3 nanocrystals was obtained under single-wavelength diode laser excitation of 976 nm. The white light consists of the blue, green, and red UC radiations which correspond to the transitions 1G4→3H6 of Tm3+, 2H11/2/4S3/2→4I15/2, and 4F9/2→4I15/2 of Er3+ ions, respectively. The UC mechanisms were proposed based on spectral, kinetic, and pump power dependence analyses. The calculated color coordinates display that white light can be achieved in a wide range of pumping powers, which promises their potential applications in the field of displays, lasers, photonics, and biomedicine. [ABSTRACT FROM AUTHOR]

To develop fluorescent labels for multicolor imaging, rare-earth-ion-doped ZrO2 nanocrystals were prepared by a complex precursor method. Laser excitation of 976 nm induced single fluorescent bands of green and red upconversion (UC) in ZrO2:Er3+ and ZrO2:Er3++Yb3+ nanocrystals, respectively. A suppression ratio (SR) parameter was introduced, defined as the UC intensity ratio of the main band to all the other detected impurity bands, and SR values in the order of 10–100 were experimentally obtained, demonstrating the excellent monochromaticity of the UC labels. Thus, the two-color UC labels obtained are potentially ideal to be used for biological multicolor imaging. [ABSTRACT FROM AUTHOR]