Ln3+ Ions Doped Phosphate Glasses For Solid State Lighting Applications

Abstract

In present study, Lanthanide ions doped oxide and oxyfluoride phosphate glasses were prepared through melt quenching technique. Subsequently, properly cut and polished samples were studied through XRD, FTIR, density, refractive index, absorption spectra, photoluminescence spectra, X-rays induced luminescence spectra, JO analysis, lifetime study and CIE coordinates analysis. The recorded XRD pattern show broad bands without any sharp peaks which show that these glasses are amorphous in nature. The FTIR results show that the band corresponding to OH vibrations decrease in oxyfluoride glass samples compared to the oxide glasses. The decrease in the intensity of OH group bands, is due to the decrease of amounts of OH in the glass composition by reaction with fluorene to produce HF. The measured density shows the overall increasing trend with increase in the rear earth concentrations and also the densities of oxide glasses are higher than the oxyfluoride glasses which show that the structures of oxide glasses are more compact than the oxyfluoride glasses. The absorption spectra (Uv-Vis-NIR region) contain the corresponding doped rare earth ions transitions peaks. For Dysprosium (Dy3+), Samarium (Sm3+) and Europium (Eu3+) ions doped glasses most intense peaks correspond to 6H15→6H9/2+6F11/2, 6H5/2→6F7/2 and 7F0→5L6 transitions, respectively. The positions of the absorption bands are slightly change with change in the glass compositions. Similarly, the recorded excitation spectra of present glasses have corresponding Sm3+, Eu3+ and Dy3+ transition peaks along with the Gd3+ ions transitions peaks. Subsequently, the recorded emission spectra show the energy transfer from excited Gd3+ ions to Dy3+, Sm3+ or Eu3+ ions present in glass compositions. The transitions 8H5/2→6P3/2, 7F0 →5L6 and 6H15/2→ 4M15/2 + 6P7/2 are the hyper sensitive transition for Dy3+, Sm3+ and Eu3+ respectively. The emission spectra recorded at the respective wavelength observed for hypersensitive transitions in excitation spectra demonstrate that the oxyfluoride glass samples show comparatively higher emission intensity. The emission intensities increase with increasing RE3+ ions concentrations up to 1 mol% in the case of Dy3+ and Sm3+ ions doping there after start decreasing. While in the case of Eu3+ ions, the emission intensity upsurges and no luminescence quenching observed in 0.0 to 2.0 mol% concentration range. It is believed that the concentration quenching occurs due to non-radiative energy transfer among the RE3+ ions through cross relaxation channels. In X-rays induce luminescence spectra studied in present work show same trend and number of emission peaks as that of photoluminescence emission spectra but with different intensity and slightly different peaks positions due to the different irradiation sources. Several radiative properties i.e., Branching ratio, quantum efficiency, radiative lifetime, stimulated emission cross sections and radiative transition probabilities were calculated with JO theory. Lifetime of present glasses were recorded with respective emission and excitations wavelength and it is found that lifetime decrease with increasing concentration of Dy3+ and Sm3+ ions, while for Eu3+ ions no significant variations observed in lifetime values. Moreover, lifetime curve shows single exponential nature at lo wer concentration of rare earth and deviate from the single exponential behavior as the concertation of rare earth increase. This non-single exponential behavior of lifetime curves are fitted in the framework of Inokuti-Hirayama (IH) model to understand energy transfer mechanism involved in respective case. Subsequently, the color of emitted light was compared with 1931 CIE (Commission International de I’Eclairage) chromatic color coordinates.