New undoped TeO 2 -La 2 O 3 -In 2 O 3 glasses were synthesized by the traditional melt-quenching method. For the specific composition (85.714 TeO 2 - 4.511 In 2 O 3 - 9.775 La 2 O 3 (mol. %)), a series of undoped and Er 3+ -doped glass-ceramic samples were elaborated via a one step heat-treatment conducted at 450°C, for different dwell times. X-ray diffraction data testify to the presence of the unique La-substituted (La,In) 2 Te 6 O 15 (LITO) fluorite-type phase, frequently labelled as “anti-glass” due to the intrinsic disorder of its anionic sub-lattice. The microstructure of these glass-ceramics can be described as crystalline micro-inclusions dispersed in a residual glass phase; the two bearing the same chemical composition, as proved by Energy Dispersive X-ray Spectroscopy analyses. The disordered character of the LITO phase was evidenced by Raman spectroscopy, confirming the adapted “anti-glass” qualification. In addition, both the near infrared and visible macroscopic photoluminescence (PL) properties of Er 3+ ions were recorded for the series of doped samples. Limited spectral variations were observed and a constant lifetime value of the 4 I 13/2 excited state was measured. Fortunately, micro-PL measurements allowed discriminating the emission for Er 3+ ions located inside the micro-inclusions from that of Er 3+ ions situated in the glassy matrix. Finally, after 12 h of heat treatment at 450°C and beyond, multiple cracks appear, leading to the degradation of the optical transmission. Surprisingly, adapting the heat treatment to higher temperatures (550°C) leads to reach a higher optical transparency. Such behaviour is explained by the phase transition from the “anti-glass” fluorite-type structure towards the bixbyite-type structure, characterized by some ordering of Te 4+ /In 3+ /La 3+ cations.
New undoped TeO2-La2O3-In2O3 glasses were synthesized by the traditional melt-quenching method. For the specific composition (85.714 TeO2 - 4.511 In2O3 - 9.775 La2O3 (mol. %)), a series of undoped and Er3+-doped glass-ceramic samples were elaborated via a one step heat-treatment conducted at 450°C, for different dwell times. X-ray diffraction data testify to the presence of the unique La-substituted (La,In)2Te6O15 (LITO) fluorite-type phase, frequently labelled as “anti-glass” due to the intrinsic disorder of its anionic sub-lattice. The microstructure of these glass-ceramics can be described as crystalline micro-inclusions dispersed in a residual glass phase; the two bearing the same chemical composition, as proved by Energy Dispersive X-ray Spectroscopy analyses. The disordered character of the LITO phase was evidenced by Raman spectroscopy, confirming the adapted “anti-glass” qualification. In addition, both the near infrared and visible macroscopic photoluminescence (PL) properties of Er3+ ions were recorded for the series of doped samples. Limited spectral variations were observed and a constant lifetime value of the 4I13/2 excited state was measured. Fortunately, micro-PL measurements allowed discriminating the emission for Er3+ ions located inside the micro-inclusions from that of Er3+ ions situated in the glassy matrix. Finally, after 12 h of heat treatment at 450°C and beyond, multiple cracks appear, leading to the degradation of the optical transmission. Surprisingly, adapting the heat treatment to higher temperatures (550°C) leads to reach a higher optical transparency. Such behaviour is explained by the phase transition from the “anti-glass” fluorite-type structure towards the bixbyite-type structure, characterized by some ordering of Te4+/In3+/La3+ cations.
A method is introduced to estimate the energy of Mn2+-to-metal charge transfer (MMCT) in 43 compounds (halides, oxides, and nitrides) for which experimental absorption or excitation bands were assumed to be of MMCT origin in a recent report. The method was originally established for trivalent lanthanides (Pr3+ and Tb3+) and for mercury-like cations (Bi3+, Sb3+ and Pb2+) in oxidic compounds where the metal acceptor has an electronic configuration d0 or d10. It is tentatively extended here to the Mn2+ ion as a dopant in oxidic or non-oxidic compounds incorporating metal acceptors with electronic configuration p6s0 (Ca2+, Mg2+, Al3+, Si4+), d0 (Y3+, Ti4+) or d10s0 (Zn2+, Cd2+, Ge4+, Sn4+). The method is found to be unapplicable for Mn2+-doped alkaline halides but confirms the Mn2+-to-metal charge transfer character of the electronic transitions in most of the compounds investigated, given a tolerance of ± 0.5 eV between experiment and calculation.
The commercialization of new phosphor materials requires far more than the discovery of emission spectra that meet the device requirement. Successful implementation depends on a rigorous understanding of human visual response, application-specific spectral requirements, and the practical realities of large-scale manufacturing. This paper outlines the critical factors that govern the evaluation and deployment of new fluorescent and LED-conversion phosphors, drawing on more than four decades of lighting-design experience and 25 years of production history. We examine the relationship between spectral power distribution and perceived brightness, including the influence of photopic, circadian, and biological receptor sensitivities. The limitations of traditional color-quality metrics such as CRI are discussed, along with the advantages of more comprehensive systems such as the Color Quality System (CQS). We will discuss a spectral-tuning case study that shows how spectral tuning can enhance perceived visual clarity even when conventional photometric metrics predict lower performance. Finally, we highlight the often-overlooked challenges of scaling phosphor synthesis from gram-scale laboratory samples to multi-kilogram or multi-ton production, emphasizing the need for early integration of manufacturability considerations in the development.
In oxide glasses, titanium can exist in multiple oxidation states and coordination environments, yet the spectroscopic signatures of lower-coordinated Ti3+ species remain poorly understood compared with the extensively studied Ti3+ in octahedral environments. In this work, aerodynamic levitation was employed to remelt ultra-low expansion (ULE) titanosilicate glass under reducing atmospheres at temperatures exceeding 2000 °C to promote reduction of tetrahedral Ti4+ to Ti3+ while preserving the intrinsically low coordination of titanium in the glass network. To establish coordination-dependent spectroscopic trends, highly polymerized Ti-doped sodium alumino/boro-silicate glasses were prepared under strongly reducing conditions by a conventional melt and quench process as model systems, while a sodium-titano-alumino-phosphate glass containing predominantly octahedral Ti3+ was used as a reference. All glasses were investigated using UV-Vis-NIR absorption, electron paramagnetic resonance (EPR), and Raman spectroscopy, complemented by density functional theory (DFT) and linear response time-dependent DFT (LR-TDDFT) computational predictions. The octahedral Ti3+ reference glass exhibits the characteristic absorption band near 523 nm and a nearly isotropic EPR signal around giso ≈ 1.92-1.94. In contrast, the reduced aluminosilicate and borosilicate glasses develop broad near-infrared absorption bands extending from ∼700-1500 nm together with EPR resonances containing high-g components approaching or exceeding g = 2.0, indicating substantial populations of lower-coordinated Ti3+ species. The reduced levitated ULE glass exhibits a dominant absorption band near 1085 nm and a rhombic Ti3+ EPR signal (gx ≈ 1.997, gy ≈ 1.942, gz ≈ 1.912), consistent with a low-symmetry and highly distorted octahedral and lower-coordinated environment. Collectively, these results provide new insight into the UV-Vis-NIR, EPR, and Raman structural characteristics of Ti3+ in different coordination environments and represent one of the first systematic efforts to distinguish lower-coordinated Ti3+ species from octahedral Ti3+ in oxide glasses.
