Quantification of excitation-power dependency in Tm^{3 +}/Yb^{3 +} doped fluorotellurite upconverting glass phosphor for iris recognition

Excitation-power dependency of upconversion (UC) photons have been quantified in Tm^{3 +}/Yb^{3 +} doped fluorotellurite (BALMT) glasses under the excitation of 975 nm laser. The net powers of three-photon-excited blue and red and two-photon-excited NIR emissions are determined to be 242, 101 and 7994 μW in 0.5 wt% Tm₂O₃ and 2 wt% Yb₂O₃ co-doping case under the excitation power of 870 mW, respectively, and the net emission photon numbers are identified to be 58.2 × 10¹³, 33.0 × 10¹³ and 3253.2 × 10¹³cps. The quantum yields (QYs) for multi-photon-excited UC emissions of Tm^{3 +} are identified as a positive dependency with pumping powers, and the relativity for three-photon fluorescence is extremely severe. When the excitation power density is set to 110.8 W/mm², the QY values for 476 nm blue and 650 nm red UC emissions are up to 1.49 × 10^{− 4} and 0.84 × 10^{− 4}, and furthermore, the value for 809 nm NIR UC emission is as high as 83.22 × 10^{− 4}. The 809 nm luminescence is one of the good matching wavelengths for iris recognition in NIR ranges, the intensive NIR luminescence and the efficient blue fluorescence are promising in scanning and positioning for iris scanning. The macroscopic quantization for UC photon generation from Tm^{3 +} in low-phonon fluorotellurite glasses provides a reliable reference for developing compact high-power-density light sources in iris recognition.