White light and energy transfer of Tm3+, Tb3+ and Sm3+ in zinc borophosphate glass

The incorporation of rare earth ions into glass materials can offer promising applications for white light emission devices. In this work, Tm2O3, Tb4O7, and Sm2O3 single and triply doped zinc borophosphate (ZBP) glasses were prepared by the melt-quenching method. The amorphous nature of the ZBP glasses was confirmed through XRD measurements. The FTIR results showed that the vitreous network is composed of BO3 and BO4 structures, symmetric and asymmetric vibrations related to phosphate groups, and vibrations in ZnO4 units. The absorption spectra present characteristic peaks of Tm3+, Tb3+ and Tm3+; the triply doped samples presented an increase of Tm3+ bands with the Tm2O3 addition. The excitation spectra of the single doped samples demonstrate that the wavelength of 357 nm is the most suitable for the excitation for the triply doped samples. Under excitation at 357 nm, the luminescence results of the single-doped samples revealed the main emission bands of the studied ions, blue, green and red. The combination of these emission colors was verified through the CIE diagram, the triply doped samples present CIE coordinates close to the ideal white region, with the best result for the ZBP - 0.5 TTS sample. The color rendering index (CRI) calculations confirmed that this sample achieved the highest value (56) among the triply doped samples, surpassing commercial LEDs, which are 22 and 38. The energy transfer efficiency (eta) and Quantum Yield (QY) for triply doped glasses was also investigated. The photoluminescence lifetime values show a decrease with increasing Tm2O3 concentration for the concentrations of 0.25-0.75 mol% of Tm2O3. The results suggest that the studied glasses have potential applications in white light emitting diodes (W-LEDs).