Luminescence lifetime based temperature sensing has an intrinsic immunity to the influence of external conditions, and dual mode thermometry is highly accurate due to its “self-calibration” merit. To develop thermometry with both features, we investigated the phase and microstructural evolution of Cr3+-doped calcium-fluorosilicate glass and glass-ceramics, which revealed different luminescent behavior relating to the different Cr3+ sites in the materials. From the photoluminescence (PL) spectra, the emission at 717 nm was derived from the O-coordinated octahedral sites, while the 1 μm super-broad emission was assigned to the F-coordinated octahedral sites. After an annealing treatment, cubic CaF2 nanocrystals were homogeneously precipitated in the glass-ceramics; thus, both the O-coordination in the residual glass phase and F-coordination in the CaF2 crystalline phase were strengthened. This led to the enhancement of both the emissions at 717 nm and 1 μm. The O-coordinated sites were relatively strong-field sites in which the fluorescence of Cr3+ originated from the radiative transitions of the two thermally coupled energy levels, 2E and 4T2, while the F-coordinated sites were relatively weak-field sites. Hence, the Cr3+ exhibits only one excited state 4T2, which is inactivated by radiative transitions and non-radiative transitions from the thermal quench. Based on the obtained results, the maximum relative temperature sensitivity coefficients are 0.76% K−1 at 498 K for the 717 nm emission and 0.47% K−1 at 351 K for the 1 μm emission. This provides the possibility of developing a dual mode temperature sensor with high precision only using a single material.

Herein, three different silver species were stably formed in SiO2–Al2O3–B2O3–Na2O–ZnF2–CaF2 glasses and were identified by their characteristic luminescence bands: violet blue luminescence (Ag+: 4d95s1 → 4d10), green white molecular fluorescence (molecule-like [Agm]n+, named ML-Ag) and orange molecular fluorescence ([Ag2]2+ pairs). Due to the relatively low aggregation degrees of [Agm]n+ and [Ag2]2+, non-radiative transitions were highly suppressed, and the PL quantum yields (QYs) of ML-Ag and [Ag2]2+ pairs reached 73.7% and 89.7%, respectively. The substitution of 0.5B2O3−0.5Na2O with SiO2 promoted the partial reduction of Ag+ to Ag0 and the subsequent aggregation of Ag+ and Ag0 to form [Agm]n+ (ML-Ag). The absence of Na2O also resulted in an increasing amount of Ag+–Ag+ pairs with closing interionic distance to form [Ag2]2+ in glass. According to the X-ray photoelectron spectra (XPS) and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra, a solubility strategy and a charge compensation model were proposed to describe the transformations between different silver species. The formation of ML-Ag was further controlled via the solubility of Ag+ in glass, whereas [Ag2]2+ centers could be effectively produced by lowering the total amount of other competitive charge compensators, such as Na+, or by introducing negatively charged [BO4]−, [AlO4]−, and [ZnO4]2− tetrahedrons into the glass matrix.

•At low doping, extra Cu+ tends to be reduced into Cu0 in phosphosilicate glasses.•At high doping, extra Cu+ tends to be oxided into Cu2+ in phosphosilicate glasses.•The oxidation of Cu+ → Cu2+ is due to the increasing of non-bridging oxygen.•Energy transfers from Cu+ to Cu2+ are primary quenching routes of the Cu+ PL.•Different Cu+ cites were revealed as [CuO6] octahedrons with tetragonal or trigonal ​ distortions.We reported a series of phosphosilicate glasses containing different Cu species (Cu0, Cu+ and Cu2+). With X-ray diffraction (XRD), Transmission electron telescope (TEM), and absorption spectra (UV–Vis), Cu0 NPs and Cu+ were identified in the glasses with low Cu concentrations (0.02; 0.04; 0.1 mol%), and Cu+ and Cu2+ were identified in the glasses with high Cu concentrations (0.2; 0.4; 0.6 mol%). Raman spectra gave a clue that the quantity of non-bridged oxygens were related with the oxidation of Cu+ → Cu2+ at high Cu concentration. With photoluminescence spectra(PL) and time resolved decay spectra, different Cu+ sites were discovered with octahedral coordination predominantly with different tetragonal distortions, and ETs from Cu+ to Cu2+ were also revealed with proposed mechanisms. The study in understanding the structural effect of Cu-doped glass on luminescence would be an important step towards the rational design of transition metal doped luminescent glasses for various applications.

•Ag was dispersed homogenously in the glass.•Eu2 + promoted the formation of ML-Ag and Ag NPs.•ET from ML-Ag enhanced the Eu3 + red emission and broadened its excitation.•The Eu/Ag-doped glass emitted warm white light with low color temperatures.The Ag/Eu singly-doped and co-doped glasses were prepared with a melt-quenching method. Silver species are identified as Ag+, molecule-like Ag nano-clusters (Ag NCs) and Ag nano-particles (Ag NPs) with surface plasmonic resonance (SPR) behaviors in the Ag-doped glasses (GAg and GAgEu) by absorption and photoluminescence spectra. Europium ions, including Eu2 + and Eu3 +, also existed in the Eu-doped glasses (GEu and GAgEu). The formation of Ag NCs was found to be effectively promoted by an accompanied oxidation of Eu2 +. This significantly enhances the super-broad visible emission of the Ag/Eu co-doped glass (GAgEu) by about 8 times than the Ag-doped glass (GAg). Owing to energy transfer from silver species (Ag+ and Ag NCs) to Eu3 +, the UV excitation of the Eu3 + red emission was enhanced and extended in 240 nm – 400 nm region. Combining the bluish white emission of Ag NCs and the red emission of Eu3 +, the Ag/Eu co-doped glass (GAgEu) emits pure white light with a low color temperature (CCT) and a high color rendering index (CRI), thus can be a candidate for LED illumination.

Tremendous enhancement of optical emission efficiency was achieved in fluorosilicate glasses by growing lanthanide doped fluoride nanocrystals embedded in oxide glass matrix. The formation mechanism of the microstructure was elucidated by combining solid-state NMR, scanning TEM, EDX map, and large-scale molecular dynamics simulations. The results reveal that the growth of fluoride nanocrystals in fluorosilicate glass was originated from fluoride phase separation. Atomic level structures of phase separation of fluoride-rich regions in oxyfluoride glasses matrix were observed from both EDX maps and MD simulations, and it was found that, while silicon exclusively coordinated by oxygen and alkali earth ions and lanthanide mainly coordinated by fluorine, aluminum played the role of linking the two fluoride glass and oxide glass regions by bonding to both oxygen and fluoride ions.

•Oxynitride glass–ceramics were prepared in Ca–Zn–Al–Si–O–N system.•CaAl2Si2O8 and Y20Si12O48N4 were homogenously dispersed in the glass–ceramics.•Eu2 + substitutes Ca2 + in CaAl2Si2O8 phase and has an emission band of f–d transition.•Eu3 + substitutes Y3 + in Y20Si12O48N4 phase and has emission peaks of f–f transitions.•The QY was enhanced by 21 times, from 2.07% (glass) to 43.33% (glass–ceramics).Novel oxynitride glass–ceramics with tremendously improved quantum yield and adjustable color coordinates were prepared with the conventional melt-and-quench method and subsequent annealing heat treatment. X-ray diffraction (XRD) and transmission electron microscopy (TEM) images revealed CaAl2Si2O8 and Y20N4Si12O48 crystalline phases were homogenously precipitated in the glass matrix. The optical absorption and photoluminescence (PL) spectrum measurements showed that a large portion of Eu3 + ions were reduced into Eu2 + which were crystallized into CaAl2Si2O8 phase during the heat treatment by substituting Ca2 + ions in them. Emission spectra evidently show that Eu2 + and Eu3 + ions were preferentially incorporated in CaAl2Si2O8 and Y20N4Si12O48 crystalline phases, respectively. This assignment was further supported by cation ionic radii and local charge balances, as well as defect chemistry considerations. The total emission intensity including both Eu2 + and Eu3 + ions was enhanced with increasing the annealing temperature, due to the conversion of Eu3 + to Eu2 + and the enhanced quantum efficiency of Eu3 + in the crystalline phase as compared to the glass matrix. As a result, the quantum yields (QYs) of the glass–ceramics were also enhanced significantly from 2.07% (the precursor glass) up to 43.33% (the maximum of the glass–ceramics). The emission ratio of Eu2 +/Eu3 + changed from < 1.0 to > 4.0, which led this novel glass–ceramics with adjustable color coordinates ranging from red to blue controlled by varying the annealing temperature.

Monolithic macroporous zirconia was synthesized through a new method involving an epoxide-driven sol–gel method accompanied by a spontaneous phase separation. The sol–gel transition utilized inorganic salt ZrCl4 as primary precursor and propylene oxide as matrix former through a ring-opening reaction. Phase separation was induced with poly-(ethylene oxide) (PEO) and its tendency was adjusted by incorporating Mg2+/Y3+ and N-methylformamide (NFA) in starting solution. The morphology of the dried gel changed from a solid nanoporous structure through a phase separated macroporous bicontinuous structure to aggregates particles when varying Mg2+ or Y3+, NFA and PEO composition. An appropriate choice of the starting composition, by which the phase separation and gelation occurred parallel, allows the fabrication of macroporous zirconia monoliths in large dimensions (Φ = 30 mm, h = 8 mm). The skeleton of the monolithic macroporous zirconia gels possess a BET surface area of 271.7 m2/g. Accordingly, the effect and mechanisms of Mg2+, Y3+ and NFA during gelation process were proposed in detail. Moreover, Mg2+ or Y3+ might also act as stabilizer to form the magnesia or yttria stabilized tetragonal or cubic zirconia after the samples were heat-treated at high temperature (800 °C).

Ce3+–Eu2+–Dy3+–Eu3+-doped fluorosilicate glass ceramics containing orthorhombic CaCeOF3 nanocrystals were prepared by annealing the precursor glass above 640 °C, along with the reduction of Eu3+ → Eu2+. Under near ultraviolet excitation, the emission bands of Eu2+ or Dy3+ were enhanced by several ten or hundred times, owing to energy transfers from Ce3+ to Eu2+ or Dy3+. The glass and glass ceramics emitted warm white light deriving from the blue, yellow and red emission from Eu2+, Dy3+ and Eu3+. Tuning the annealing temperature, the Eu2+/Eu3+ ratio and the warm white Commission Internationale de I’Eclairage (CIE) coordinates can be adjusted. Thus, the present materials can be applied on warm white high power light-emitting-diodes for indoor illumination application.Highlights►Orthorhombic CaCeOF3 nanocrystals were precipitated in the Ce/Dy/Eu doped glass. ► The reduction of Eu3+ →Eu2+ took place along with the annealing process. ► The Eu2+/Eu3+ ratio can be fine adjusted by tuning the annealing temperature. ► ETs from Ce3+ enhanced emission of Eu2+ or Dy3+by several ten or hundred times. ► The glass ceramics emit warm white light with tunable CIE coordination.

Cr3+/Yb3+-codoped glasses were studied as broadband down shifting materials for improving solar cells’ efficiency. We observed Föster resonance energy transfers (FRET) from Cr3+: 4T2g to Yb3+: 2 F5/2. The ET efficiency was up to 84 %, and the measured quantum yield (QY) reached 21.51 %. The glass can convert solar photons in super wide UV–Vis range to near infrared photons with the minimum quantum yields larger than 10%. Thus, such materials can be applied for improving silicon solar cells’ conversion efficiency.Highlights► The Cr3+/Yb3+-codoped glass has a broad UV–VIS excitation band. ► The glass can convert UV–VIS solar photons to solar-cell-utilizable NIR photons. ► Föster resonance energy transfers (FRET) exist between Cr3+: 4T2g and Yb3+: 2 F5/2. ► FRET efficiency is up to 84 % and the quantum yield reaches 21.51 %.

The Eu2 +/Tb3 +/Eu3 + co-doped fluorosilicate glass ceramics containing SrLaF5 nanocrystals were prepared. XRD results showed the rare earth ions were enriched into the precipitated nanophase. It deduced efficient energy transfers (ET) from Eu2 + to Tb3 + and Eu3 + and intense warm white luminescence of the glass ceramics. Comparing the glass, the luminescence quantum yield (QY) of the glass ceramics was enlarged by about 3 times. That demonstrated the potential WLED application of the present glass ceramics.Highlights► We report a new glass ceramics containing SrLaF5: Eu2 +, Tb3 +, Eu3 + nanocrystals. ► Eu2 + substitutes Sr2 +, and Tb3 +/Eu3 + substitutes La3 + in SrLaF5. ► Under UV excitation, energy transfers efficiently from Eu2 + to Tb3 + and Eu3 +. ► The glass ceramics emit intense warm white light with tunable CIE coordinates. ► The PL quantum yield of the glass ceramics is about 3 times of the glass.

The preparation and upconversion luminescence properties of the Yb3+ and Tb3+ co-doped glass ceramics containing SrF2 nanocrystals were investigated. The formation of SrF2 nanocrystals was confirmed by X-ray diffraction and transmission electron microscopy. Both microstructural and spectral analysis indicated that the Yb3+ and Tb3+ ions were enriched in the precipitated SrF2 nanocrystals, which provide much lower phonon vibration energy than the glass matrix. Due to the efficient cooperative sensitization from Yb3+ to Tb3+ and the relatively low maximum phonon energy of SrF2 nanocrystals, the Yb3+ and Tb3+ co-doped glass ceramics exhibited intense upconversion luminescence, including ultraviolet emission at 382 nm.HighlightsWe report an Yb3+/Tb3+ co-doped glass ceramics containing SrF2 nanocrystals. ► Yb3+ and Tb3+ are incorporated in the nanocrystals by annealing method. ► It deduced intense UV–vis upconversion luminescence. ► The upconversion mechanism is the cooperative sensitization from Yb3+ to Tb3+. ► The glass ceramics exhibit higher ET efficiencies than the glasses.

The preparation and upconversion luminescence properties of the Yb3+ and Tb3+ co-doped glass ceramics containing SrF2 nanocrystals were investigated. The formation of SrF2 nanocrystals was confirmed by X-ray diffraction and transmission electron microscopy. Both microstructural and spectral analysis indicated that the Yb3+ and Tb3+ ions were enriched in the precipitated SrF2 nanocrystals, which provide much lower phonon vibration energy than the glass matrix. Due to the efficient cooperative sensitization from Yb3+ to Tb3+ and the relatively low maximum phonon energy of SrF2 nanocrystals, the Yb3+ and Tb3+ co-doped glass ceramics exhibited intense upconversion luminescence, including ultraviolet emission at 382 nm.HighlightsWe report an Yb3+/Tb3+ co-doped glass ceramics containing SrF2 nanocrystals. ► Yb3+ and Tb3+ are incorporated in the nanocrystals by annealing method. ► It deduced intense UV–vis upconversion luminescence. ► The upconversion mechanism is the cooperative sensitization from Yb3+ to Tb3+. ► The glass ceramics exhibit higher ET efficiencies than the glasses.