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This work investigates the optical properties of Yb3+ ions doped GeO2-PbO glasses containing Ag nanoclusters (NCs), produced by the melt-quenching technique. The lack in the literature regarding the energy transfer (ET) between these species in these glasses motivated the present work. Tunable visible emission occurs from blue to orange depending on the Yb3+ concentration which affects the size of the Ag NCs, as observed by transmission electron microscopy. The ET mechanism from Ag NCs to Yb3+ ions (2F7/2 → 2F5/2) was attributed to the S1→T1 decay (spin-forbidden electronic transition between singlet–triplet states) and was corroborated by fast and slow lifetime decrease (at 550 nm) of Ag NCs and photoluminescence (PL) growth at 980 nm, for excitations at 355 and 405 nm. The sample with the highest Yb3+ concentration exhibits the highest PL growth under 355 nm excitation, whereas at 410 nm it is the sample with the lowest concentration. The restriction of Yb3+ ions to the growth of NCs is responsible for these effects. Thus, higher Yb3+ concentration forms smaller Ag NCs, whose excitation at 355 nm leads to more efficient ET to Yb3+ ions compared to 410 nm. These findings have potential applications in the visible to near-infrared regions, such as tunable CW laser sources and photovoltaic devices.

The present work shows the development of technology for the production of silver (Ag) nanoclusters in GeO2-PbO glasses codoped with Tm 3+ and Yb 3+ ions and doped with Tm 3+ ions. The samples were produced by the melt quenching followed by rapid cooling, using a temperature lower than the glass transition one for the heat treatment, in order to favor the formation of Ag nanoclusters; the samples were characterized by measurements of absorption, luminescence, lifetime and transmission electron microscopy. The absorption measurements identified the incorporation of rare-earth ions in the trivalent form. The identification of the aforementioned nanoclusters and amorphous structure was performed by transmission electron microscopy and electron diffraction analysis, respectively; Through luminescence measurements made under different conditions (different lasers operating at 355 and ~ 400 nm, UV lamp and fluorimeter) the emission of Ag nanoclusters and correlation with their concentration and excitation wavelength were studied. The energy transfer mechanism between the nanoclusters and the aforementioned Tm 3+ and Yb 3+ ions was studied with the aid of luminescence and lifetime measurements. Different light emission from Ag nanoclusters at different excitation wavelengths (340-400 nm) indicate the formation of nanoclusters of different sizes; the same occurs when we increase the concentration of Ag nanoclusters, which leads to an increase in their dimensions and luminescence at longer wavelengths. It should be added that in the presence of rare-earth ions, it was possible to observe the emission of white light for excitation at 365 nm, performed by a UV lamp. Energy transfer from nanoclusters to Tm 3+ ions was confirmed by the luminescence growth at 800 nm, being more significant in the absence of Yb 3+ ions, for excitations at 380 and 400 nm. The decrease in the lifetimes of Ag nanoclusters and the increase in the lifetimes of the Tm 3+ ions, corroborated these energy transfers. The energy transfer from the nanoclusters to the Yb 3+ ions(980nm) were also observed through the luminescence and lifetime results, for excitation at ~ 400 nm, being more significant for the highest concentration of nanoclusters. The present results demonstrate for the first time the possibility of producing Ag nanoclusters in GeO2-PbO glasses, energy transfer to rare-earth ions, corroborating the potential of these materials for photonics and opens perspectives for further studies with different rare-earth ions.