Up and down-shifting emission properties of novel Er³⁺-doped CdO-V₂O₅-P₂O₅ glass system

Er³⁺-doped CdO-V₂O₅-P₂O₅ novel glass samples, with high amount of CdO (90 mol%), were fabricated by the melt-quenching method. The glassy structure was confirmed by X-rays diffraction patterns and Raman spectra. A detailed analysis of the Raman Spectra showed that these samples are mainly constituted by amorphous Cd₂V₂O₇ and PO₄ units. By optical absorption, band gap (E_g) values in the 2.44–2.63 eV range were determined, depending on the Er³⁺ concentration. Upon 980 nm diode laser excitation, the up-conversion spectra displayed the well-known erbium (⁴S_3/2,²H_11/2) → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions in the 510–575 and 640–690 nm range, whereas the down-shifting emission spectra in the near infrared (NIR) region showed a broad band extending from 1440 to 1650 nm, attributed to the Er³⁺: ⁴I_13/2 → ⁴I_15/2 transition. Both spectra reached the highest intensity at 2.5 mol% of Er³⁺. For higher Er³⁺ concentrations, the emission intensities were gradually reduced, which is associated with non-radiative and cross relaxation processes. This fact was verified by the shortening of the green and NIR emission decays recorded under 488 and 980 nm pulsed laser excitation. The mechanism involved in the cross relaxation of the NIR emission, was analyzed by fitting the emission decays with the Inokuti-Hirayama model, which revealed that dipole-dipole electric interactions might dominate the cross-relaxation processes within Er-Er clusters.