Investigation of Upconversion, downshifting and quantum -cutting behavior of Eu3+, Yb3+, Bi3+ co-doped LaNbO4 phosphor as a spectral conversion material

Photoluminescence behavior of rare earth doped self-activated phosphors (i.e. niobate and vanadate) and their applications

In the present study, the photoluminescence behaviors of rare earth doped self-activated phosphors are discussed briefly. Different techniques were used to develop these phosphor samples. We prepared pure and rare earth doped phosphor samples to look for their various applications. The structural confirmations and surface morphologies were performed using X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements, respectively. The upconversion (UC) phenomenon was investigated in Tm³⁺/Yb³⁺ and Ho³⁺/Yb³⁺ co-doped niobate and vanadate based phosphors, which gave intense blue/NIR and green/red emissions with a 980 nm diode laser as an excitation source. Pure niobate and vanadate phosphor materials are self-activated hosts which give broad blue emission under UV excitation. Upon UV excitation, intense broad blue emission along with sharp emissions due to Tm³⁺ and Ho³⁺ ions are observed via energy transfer between niobate/vanadate and rare earth ions. These self-activated hosts show prominent downshifting (DS) behavior. Broad band quantum cutting (QC) was observed in these self-activated hosts, in which a blue emitting photon is converted into two NIR photons by co-doping Yb³⁺ ions in it. The multimodal (upconversion, downshifting and quantum cutting) behaviors of these phosphors make them very promising in various applications, such as spectral converters to enhance the efficiency of a c-Si solar cell, security ink and color tunable materials.

Optical band gaps and spectroscopy properties of Bi m+/Eu n+/Yb3+ co-doped (m = 0, 2, 3; and n = 2, 3) zinc calcium silicate glasses

In this study, the indirect/direct optical band gaps and spectroscopy properties of Bi ^m+/Eu ⁿ⁺/Yb³⁺ co-doped (m = 0, 2, 3; and n = 2, 3) zinc calcium silicate glasses under different excitation wavelengths were investigated. Zinc calcium silicate glasses with the main compositions of SiO₂-ZnO-CaF₂-LaF₃-TiO₂ were prepared by the conventional melting method. EDS analysis was performed to determine the elemental composition existing in the zinc calcium silicate glasses. Visible (VIS)-, upconversion (UC)-, and near-infrared (NIR)-emission spectra of Bi ^m+/Eu ⁿ⁺/Yb³⁺ co-doped glasses were also investigated. Indirect optical band gaps and direct optical band gaps of Bi ^m+-, Eu ⁿ⁺- single-doped, and Bi ^m+-Eu ⁿ⁺ co-doped SiO₂-ZnO-CaF₂-LaF₃-TiO₂-Bi₂O₃-EuF₃-YbF₃ zinc calcium silicate glasses were calculated and analyzed. CIE 1931(x, y) color coordinates for VIS and UC emission spectra of Bi ^m+/Eu ⁿ⁺/Yb³⁺ co-doped glasses were determined. Besides, the mechanism of VIS-, UC-, NIR-emissions, and energy transfer (ET) processes between Bi ^m+ and Eu ⁿ⁺ ions were also proposed and discussed.