Emission properties of hydrothermal Yb3+, Er3+ and Yb3+, Tm3+-codoped Lu2O3 nanorods: upconversion, cathodoluminescence and assessment of waveguide behavior

Yb3+ and Ln(3+) (Ln(3+) = Er3+ or Tm3+) codoped Lu2O3 nanorods with cubic Ia (3) over bar symmetry have been prepared by low temperature hydrothermal procedures, and their luminescence properties and waveguide behavior analyzed by means of scanning near-field optical microscopy (SNOM). Room temperature upconversion (UC) under excitation at 980 nm and cathodoluminescence (CL) spectra were studied as a function of the Yb+ concentration in the prepared nanorods. UC spectra revealed the strong development of Er3+ F-4(9/2) --> I-4(15/2) (red) and Tm3+ (1)G(4) --> H-3(6)(blue) bands, which became the pre-eminent and even unique emissions for corresponding nanorods with the higher Yb3+ concentration. Favored by the presence of large phonons in current nanorods, UC mechanisms that privilege the population of F-4(9/2) and (1)G(4) emitting levels through phonon-assisted energy transfer and non-radiative relaxations account for these observed UC luminescence features. CL spectra show much more moderate development of the intensity ratio between the Er3+ F-4(9/2) --> I-4(15/2) (red) and H-2(11/2), S-4(3/2) --> I-4(15/2) (green) emissions with the increase in the Yb3+ content, while for Yb3+, Tm3+-codoped Lu2O3 nanorods the dominant CL emission is Tm3+ D-1(2) --> F-3(4) (deep-blue). Uniform light emission along Yb3+, Er3+-codoped Lu2O3 rods has been observed by using SNOM photoluminescence images; however, the rods seem to be too thin for propagation of light.