Development of sodium-zinc phosphate glasses doped with Dy3+, Eu3+ and Dy3+/Eu3+ for yellow laser medium, reddish-orange and white phosphor applications

A spectroscopy analysis of Eu2O3 (2.0 mol%) or Dy2O3 (2.0 mol%) singly-doped and Dy2O3 (2.0 mol%)/Eu2O3 (2.0 mol%) codoped sodium-zinc phosphate glasses is performed through their Raman, absorbance and photoluminescence spectra, and decay times. The phonon energy (1124 cm(-1)) and electron-phonon coupling strength (0.028) of the glass host were determined using phonon side band spectroscopy. Laser parameter values (stimulated emission cross section, effective bandwidth, gain bandwidth and optical gain), obtained for the F-4(9/2) -> H-6(13/2) yellow emission of the Dy3+ singly-doped glass, are higher than those reported for others 2 mol% Dy2O3-doped oxide glasses, so that the magnitudes of such parameters could be suitable for a low threshold and a high gain of yellow laser emission. Additionally a value of the quantum efficiency close to the unity (0.96) was found for the dysprosium F-4(9/2) level luminescence. The intense yellow emission relative to the F-4(9/2) -> H-6(15/2) blue one leads to the Dy3+ singly-doped glass to emit neutral white light of 4647 K upon 349 nm excitation. The Eu3+ singly-doped glass can emit reddish-orange light of 2166 K and red color purity of 97.7% upon 394 nm excitation, whose (0.642, 0.351) CIE1931chromaticity coordinates are close to those (0.67, 0.33) of the red phosphor proposed by the National Television Standard Committee. The Dy3+/Eu3+ codoped glass emission color can be tuned from warm white light of 3628 K upon 349 nm excitation to reddish-orange light of 1891 K after 364 nm excitation. The warm white light emission is generated mainly by the transitions F-4(9/2) -> H-6(13/2), H-6(15/2) of Dy3+ and D-5(0) -> F-7(2) of Eu3+, where Eu3+ is sensitized by Dy3+ through non-radiative energy transfer with an efficiency of 0.22. An electric dipole-dipole interaction into Dy3+-Eu3+ clusters might be the dominant mechanism in the Dy3+ to Eu3+ energy transfer. Excitations at 349, 364 and 394 nm can be obtained with AlGaN, GaN and InGaN based LEDs, respectively, and therefore Dy3+ and/or Eu3+ doped sodium-zinc phosphate glasses pumped by UV LEDs could be appropriate for solid state lighting technology as neutral/warm white and reddish-orange light sources.