WHITE UPCONVERSION LUMINESCENCE FROM (Yb³⁺/Tm³⁺/Ho³⁺) TRIDOPED GdF₃ NANORODS AFTER HEAT TREATMENT

A series of Ho³⁺/Yb³⁺/Tm³⁺ tridoped GdF ₃ nanorods with different dopant concentrations were synthesized by a hydrothermal method. Transmission electron microscope (TEM) images indicate that the length and diameter of the nanorods is about 90 nm and 31 nm, respectively on average. No bright white upconversion light was observed from the samples with different Yb ³⁺, Ho ³⁺ or Tm ³⁺ concentrations. Unexpectedly, the emission color coordinates of the samples after heat treatment move toward the central white region of the chromaticity diagram, and among these samples, the color coordinate (0.349, 0.329) of GdF ₃:15% Yb ³⁺, 0.1% Ho ³⁺, 0.8% Tm ³⁺ is the most close to the standard white light (0.333, 0.333). This is unlike previous reports in which white light was achieved via tuning dopant concentration or excitation power. The reasons for the above phenomenon are presented by means of FT-IR spectra and the energy level diagram of dopants.