Spectroscopic properties of Tm:Bi4Ge3O12 crystals grown by the micro-pulling-down method

Highlights: • Tm:BGO crystals with different Tm³⁺ concentration were grown by the micro-pulling-down method. • The effect of Tm³⁺ concentration on the growth, structure and spectroscopic properties of Tm:BGO crystals was studied. • Tm:BGO crystals exhibit two fluorescence bands corresponding to the ³H₄ → ³F₄ and the ³F₄ → ³H₆ transitions. Tm³⁺-doped bismuth germanate crystals (Tm:BGO) with various doping concentrations of 0.5, 0.75, 1.0, 1.5, and 2.0 at.% were grown by the micro-pulling-down method (μ-PD). The effect of thulium concentration on the growth, structure, absorption spectra, emission spectra and fluorescence lifetime of ³H₄ and ³F₄ state was studied. Under excitation of 792 nm, Tm:BGO crystals exhibit two fluorescence bands corresponding to the ³H₄ → ³F₄ and the ³F₄ → ³H₆ transitions. The fluorescence lifetime of ³H₄ state decreased strongly as the thulium concentration increased, while the lifetime of ³F₄ state was relatively constant for all thulium concentrations.