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 970nm. 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 I11∕24(Er) state, the suppressed cross relaxation H11∕22(Er)+I15∕24(Er)→I9∕24(Er)+I13∕24(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.
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 I413/2 state experimentally demonstrates our proposed model.
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