last decades in search of improvements in the luminescent properties of europium given its relevance for optical device applications [1][2][3][4][5][6][7][8][9][10][11][12][13]. Malta et al. [1] irst reported that an improved photoluminescence (PL) of Eu 3+ ions in glass containing Ag nanoparticles (NPs) occurred due to the surface plasmon resonance (SPR) of the silver particles.Other groups subsequently concluded similarly on the role of local-ield efects of plasmonic Ag particles amplifying Eu 3+ PL in glasses [2,3,5,10,11,13]. On the other hand, several other studies have added to the discussion with respect to the conditions and mechanisms by which Eu 3+ emission is enhanced by the presence of silver [4,[6][7][8][9]12]. Namely, ionic metal species have been argued to be at the origin of energy transfer processes leading to a sensitized Eu 3+ PL rather than the Ag NPs themselves. Moreover, the NPs have been reported to instead lead to an eicient PL quenching of the rare-earth ions [4, 6] through an energy transfer/deactivating efect recently referred to as the plasmonic diluent efect [14]. Hence, achieving the desired enhanced optical properties is not straightforward. Moreover, it requires signiicant research eforts towards understanding the fundamental interactions between europium ions and the diferent oxidation and aggregation states of silver.Silicate [1-3, 7, 9, 12], borate [8], tellurite [10,11], and germanate [5] glasses were often the object of investigation regarding the interaction between europium and silver species. However, phosphate-based glass hosts notable for their high metal solubility, low-melting character, relatively low glass transition temperature, and high thermal stability are promising materials in the ield of photonics [13,15]. In these, the addition of aluminium oxide as a less acid network former results in a strengthened glass network with improved chemical durability and thermo-mechanical stability [16][17][18]. In addition, co-doping with SnO is believed Abstract The optical properties of Eu 3+ -doped aluminophosphate glass containing a high concentration of Ag 2 O and SnO co-dopants (8 mol% of each) are reported. Glass preparation is carried out by melt-quenching, and a subsequent in situ monitored heat treatment (HT) is carried out for the reduction of ionic silver to Ag nanoparticles (NPs) via reducing agent tin(II). An enhanced ultraviolet broadband excitation range for Eu 3+ ions is realized for the meltquenched glass, likely due to the creation of molecule-like silver species such as Ag + -Ag + dimers. The real-time optical monitoring of the glass during isothermal HT shows the steady development of the surface plasmon resonance peak of Ag NPs near 420 nm. Concurrently exciting Eu 3+ ions in situ at 420 nm unveils the plasmonic diluent efect manifested through the quenching of Eu 3+ luminescence. The decay times of the 5 D 0 emitting state in Eu 3+ ions in the melt-quenched and NP-doped glasses are measured and discussed.
