Photoluminescence of rare-earth ion (Eu ³⁺ , Tm ³⁺ , and Er ³⁺ )-doped and co-doped ZnNb ₂ O ₆ for solar cells

Abstract

Visible converted emissions produced at an excitation of 286 nm in ZnNb2O6 ceramics doped with rare-earth ions (RE = Eu3+, Tm3+, Er3+ or a combination of these ions) were investigated with the aim of increasing the photovoltaic efficiency of solar cells. The structure of RE:ZnNb2O6 ceramics was confirmed by x-ray diffraction patterns. The undoped ZnNb2O6 could emit a blue emission under 286-nm excitation, which is attributed to the self-trapped excitons’ recombination of the efficient luminescence centers of edge-shared NbO6 groups. Upon 286-nm excitation, Eu:ZnNb2O6, Tm:ZnNb2O6, and Er:ZnNb2O6 ceramics showed blue, green, and red emissions, which correspond to the transitions of 5D0 → 7FJ (J = 1−4) (Eu3+), 1G4 → 3H6 (Tm3+), and 2H11/2/4S3/2 → 4I15/2 (Er3+), respectively. The calculated CIE chromaticity coordinates of Eu:ZnNb2O6, Tm:ZnNb2O6, and Er:ZnNb2O6 are (0.50, 0.31), (0.14, 0.19), and (0.29, 0.56), respectively. RE ion-co-doped ZnNb2O6 showed a combination of characteristic emissions. The chromaticity coordinates of Eu/Tm:ZnNb2O6, Eu/Er:ZnNb2O6, and Tm/Er:ZnNb2O6 were calculated to be (0.29, 0.24), (0.45, 0.37), and (0.17, 0.25).

Structural and photoluminescence studies on europium-doped lithium tetraborate (Eu:Li 2 B 4 O 7 ) single crystal grown by microtube Czochralski (μT-Cz) technique

“…To characterize the true color emitted nature of the material, it is necessary to study the color coordinates marked on a standard chromaticity diagram. [21] The CIE 1931 (Commission International d'Eclairage) diagram is a universal method to represent all the possible colors by combining three primary colors and is used to quantify the tunability of emission wavelength and the change in intensity of the emission band. The emission intensities of the Eu-doped LTB crystals are characterized through a CIE 1931 color chromaticity diagram.…”