The effects of delayed annealing on the luminescent activity of heavy metal cadmium zinc phosphate glasses activated by: Er3+ and Tb3+ ions

Abstract

The luminescent spectra of the RE₂O₃-doped P₂O₅-CdO-ZnO glasses (RE = Er, and Tb) were investigated to separate the effects of two studied rare-earth elements and the annealing regime on the emission performance of the prepared glasses. The glasses undergo a series of collective measurements including UV-visible absorption, luminescence, thermal expansion, XRD, TEM, and FTIR. The optical UV-visible spectra of the two doped glasses reveal a UV band due to undoped glass beside and extra extended 11 peaks with the Er³⁺ ions with high distinct features while the Tb³⁺ ions samples exhibit peaks within the visible region. These peaks are correlated with transitions from the ground state in each case to specific energy transitions. The overall optical data indicate that the two rare earth ions are present in a stable trivalent state. Under UV excitation, both Er³⁺ and Tb³⁺ emit a characteristic green light corresponding to ⁴S_3/2 → ⁴I_15/2 and ⁵D₄ → ⁷F₅ transitions, respectively. The performance of the green light was identified to be enhanced by increasing the concentration of rare earth and the effect of annealing temperature. Moreover, the intensity of the infrared emission of Er³⁺ at 1532 nm corresponds to the (⁴I_13/2 → ⁴I_15/2) transition which is assumed to be developed with the effect of heating. The resultant IR spectra show distinct vibrational peaks due to phosphate groups that undergo only minor modifications when doped with rare earth elements or over-annealed.

Keywords: Annealing; Glass; Heavy metal oxide; Luminescence; Phosphate; Rare-Earth.

Figure 1

UV–visible absorption spectra of undoped and Er₂O₃ doped cadmium zinc phosphate glasses where (a) undoped, (b) UV–visible full absorption range, and (c) magnification of 200–300 range.

Figure 2

UV–visible absorption spectra of undoped and Tb₂O₃ doped cadmium zinc phosphate glasses where (a) UV–visible full absorption range and (b) Magnification of 300–550 range.

Figure 3

Excitation spectra of Er₂O₃ doped glasses where (a) 0.5 mol % and (b) 1 mol % annealed at 320 °C while (c) 0.5 mol % and (d) 1 mol % annealed at 650 °C.

Figure 4

Emission spectra of Er₂O₃ doped glasses where (a) 0.5 mol % and (b) 1 mol % annealed at 320 °C while (c) 0.5 mol % and (d) 1 mol % annealed at 650 °C.

Figure 5

NIR-emission spectra at 980 nm laser excitation of Er₂O₃ doped glasses where (a) 0.5 mol % and (b) 1 mol % annealed at 320 °C while (c) 0.5 mol % and (d) 1 mol % annealed at 650 °C.

Figure 6

Excitation spectra of 0.5 and 1% Tb₂O₃ doped glasses at different annealing temperatures where (a) covers the total range 200–500 nm and (b) magnification for spectrum range 300–500 nm.

Figure 7

Emission spectra of Tb₂O₃ doped glasses where (a) 0.5 mol % and (b) 1 mol % annealed at 320 °C while (c) 0.5 mol % and (d) 1 mol % annealed at 650 °C.

Figure 8

CIE-chromaticity diagram and overview emission spectra of Er³⁺ and Tb³⁺—doped glasses (details of coordinates are listed in Table 3).

Figure 9

Thermal expansion of the selected 1% rare–earth doped glass at 320 and 650 °C annealing temperatures.

Figure 10

XRD of the thermally heated glasses where (a) undoped, (b) 1% Er₂O₃, and (c) 1% Tb₂O₃—doped glasses after annealing at 650 °C.

Figure 11

SEM and EDAX spectrum of the thermally treated glasses where (a) undoped, (b) 1% Er₂O₃, and (c) 1% Tb₂O₃—doped glasses after annealing at 650 °C.

Figure 12

FTIR of the prepared glasses at normal annealing conditions where (a) undoped, (b) 1% Er₂O_3, and (c) 1% Tb₂O₃ after annealing at 320 °C.

Figure 13

FTIR of the thermally treated 1% rare-earth doped—glasses where (a) undoped, (b) Er₂O_3, and (c) Tb₂O₃ after annealing at 650 °C.