Blue and red emission in wide band gap BaZrO₃:Yb ³⁺,Tm³⁺

Under NIR excitation at 967 intense blue and red photoluminescence (PL) emissions are observed at room temperature in codoped Tm³⁺-Yb ³⁺ barium zirconate (BaZrO₃:Yb,Tm) powders. Powders were prepared by a simple hydrothermal method, and present a wide band gap that depends on the total rare earth content due to the degree of disorder induced in the BaZrO₃ lattice by the substitution of the rare earth ions. Rietveld refinements of the XRD patterns indicated the presence of primary nanocrystallites with sizes between 50 and 70 nm depending on the Tm ³⁺ content. Scanning transmission electron microscopy (STEM) shows that these primary particles self-aggregated in larger secondary particles which present a regular morphology with sizes around 1 μm. The intense blue and red PL emissions in BaZrO₃ powders under 967 nm excitation are governed by energy transfer processes from Yb³⁺ ions to Tm ³⁺ ions and crossrelaxation among Tm³⁺ ions.