The photoluminescence studies of Gd3+/Tb3+ co-doped xerogels and nano-glass-ceramics dedicated for green-emitting devices

In this work, we reported the results of photoluminescent and structural investigations of Gd³⁺/Tb³⁺ co-doped silicate xerogels as well as derivative SiO₂-LaF₃ nano-glass-ceramics. The molar ratio of appropriate acetates used during the synthesis, i.e., La(AcO)₃:Gd(AcO)₃:Tb(AcO)₃ was fixed to x:(0.95-x):0.05. Based on XRD measurements, the crystallization of hexagonal LaF₃ nanophase was verified without any admixture of GdF₃ phase, even for samples with La³⁺:Gd³⁺ molar ratio ≤1. The optical characterization of fabricated Gd³⁺/Tb³⁺ co-doped sol-gel materials involved the registration and analysis of photoluminescence excitation (PLE) and emission spectra (PL), as well as the decay curves for the ⁶P_7/2 (Gd³⁺) and the ⁵D₄ (Tb³⁺) excited levels. Upon excitation at λ_ex = 275 nm wavelength, the fabricated sol-gel samples revealed the series of emission lines assigned to the electronic transitions from both dopants, i.e., Gd³⁺ and Tb³⁺, indicating apparently the occurrence of Gd³⁺/Tb³⁺ energy transfer process (ET). The photoluminescence measurements comprehensibly proved the competitiveness between Gd³⁺ and Tb³⁺ ions to be entered into LaF₃ fluoride nanocrystal lattice, formed during annealing of as-prepared xerogels. Based on the recorded PL spectra for fabricated sol-gel samples, some chromatic parameters were calculated, i.e., chromaticity coordinates (CIE), correlated color temperatures (CCT), and color purities (CP). The prepared Gd³⁺,Tb³⁺ co-doped samples are able to emit green light with CCT values in a range from 5967 K to 6291 K, and high CP reached 70 %, which predispose them for use as efficient constituents for developing green-emitting devices.