Guojun Gao

Karlsruhe Institute of Technology | KIT · Institute of Microstructure Technology

A ratiometric optical thermometer based on triply‐doped La2O3:Yb³⁺/Er³⁺/Nd³⁺ microcrystals is reported with a relative sensitivity above 1% K⁻¹ in the entire range from 300–700 K, and is between 1.8–0.7% K⁻¹ over the range 290–833 K. The 825 nm upconversion (UC) emission from the Nd3+ 4F5/2 level relies on thermally‐assisted energy transfer from Yb...

Thermal images generated from infrared radiation are useful for monitoring many processes; however, infrared cameras are orders of magnitude more expensive than their visible counterparts. Methods that allow visible cameras to capture thermal images are therefore of interest. In this contribution, thermal images of a surface coated with an inexpens...

In photon upconversion (UC) based on triplet-triplet annihilation, the upconversion photo luminescent quantum yield (UC-PLQY) depends on the excitation power density in a way that can be described by a single figure of merit. This figure of merit, the threshold value, allows the excitation power density required for efficient UC-PLQY to be compared...

Supplementary Information for Critical Power Density:A Metric to Compare the Excitation Power Density Dependence of Photon Upconversion in Different Inorganic Host Materials

Supporting information for "A method for correcting the excitation power density dependence of upconversion emission due to laser-induced heating

A series of Yb-doped silica glasses containing equimolar amounts of P2O5 and Al2O3 were prepared using a sol–gel method combined with high-temperature sintering. Raman spectroscopy confirmed the formation of AlPO4 join with a P/Al ratio of 1. However, for a P/Al ratio slightly larger than 1, both the AlPO4 join and P=O bond are formed. Based on the...

Single‐band green upconversion (UC) with high green purity and color stability is urgently required for plastic recycling and anticounterfeiting. However, it is very difficult to obtain single‐band green emission for benchmark Yb³⁺/Er³⁺ activated UC materials (such as NaYF4:Yb³⁺,Er³⁺) due to the strong accompanying red UC. Herein, highly efficient...

Efficient single-band NIR-to-NIR UC emission is strongly desired for many applications such as fluorescent markers, plastic recycling, and biological imaging. Herein, we report highly-efficient single-band NIR-to-NIR UC emission in La2O3:Yb3+,Tm3+ (LYT) microcrystals. Under 980 nm laser excitation, LYT exhibits NIR UC emission at ~795 nm (Tm3+: 3H4...

We report a 30 cm long Nd 3 + / Yb 3 + co-doped silica glass fiber amplifier with well-maintained broadband gain through simultaneous dual-laser pumping at 808 and 975 nm. By controlling the ratio of the pump power at 975 ( P 975 ) and 808 nm ( P 808 ), the emission band of Yb 3 + / Nd 3 + and the energy transfer efficiency of Nd 3 + → Yb 3 + can b...

Upconversion (UC) materials enable the emission of a higher energy photon following the absorption of two or more lower-energy photons. The efficiency of UC is non-linear as it depends on the power density of the optical excitation. Hence, the measurement of the UC intensity as a function of excitation power density is a standard material character...

The laser behavior of a centimeter-scale Er 3 + / Al 3 + codoped silica fiber with core numerical aperture and core diameter of 0.15 and 8 μm, respectively, is reported. The core glass was prepared by the sol–gel method combined with high-temperature sintering; it contained Er 3 + ion concentration as high as 1.32 × 10 20 ions / cm 3 and an Al/Er m...

Absolute quantum efficiency (QE) of upconversion (UC) materials is still limited to ~3%, which strongly limits their applications in many areas. Herein, we report on highly efficient UC β-NaYF4:Yb3+,Er3+ micro-cylinders with absolute QE as high as ~4.0% via newly developed Li+/Na+ ion exchange method (IEM). Small amount of Li+ is interstitially inc...

High purity green upconversion (UC) materials have wide applications in fluorescent labels, plastic recycling, displays, etc. However, Yb3+/Er3+ based UC materials yield poor color purity in green and their output color is normally unstable with excitation power density, which withdraws their applications in aforementioned areas. Herein, we report...

Non-contact ratiometric thermometry has applications ranging from in-situ physiological measurements to industrial process monitoring. The technique is based on the optical detection of the fluorescence intensity ratio (FIR) of two thermally-coupled levels (TCLs). Here, we report a Yb³⁺/Nd³⁺ co-doped La2O3 microcrystal ratiometric thermometer that...

This work demonstrates the development of novel up-conversion (UC) and downshifting (DS) micro-scale photonic markers for the unique fluorescent labelling of polymers to realize both high-yield and high-purity recycled product.

The investigation of efficient red phosphors is highly desired for the development of novel warm white light emitting diodes (WLEDs). In this paper, we report on an efficient red phosphor of Mn4+-activated BaTiF6 by a facile co-precipitation method as a promising candidate for warm white LEDs. BaTiF6:xMn4+ phosphors show efficient pure red emission...

Output power scaling of single mode large mode area (LMA) photonic crystal fiber (PCF) amplifiers urgently requires the low refractive index of Yb³⁺-doped silica glasses whilst maintaining high optical homogeneity. In this paper, we report on a promising alternative Yb³⁺/Al³⁺/F–/P⁵⁺-co-doped silica core-glass (YAFP), which is prepared by modified s...

Up-conversion (UC) materials whose emission color can be finely-tuned while a high UC quantum efficiency is maintained are desirable for many applications, but are especially sought after as photonic markers. Herein, we report near-infrared-to-visible La2O3:Yb3+,Er3+ (LYE) UC materials with a high internal quantum yield (UCQY) of 3.8 %, external UC...

Monodisperse β-NaYF4:Yb3+,Tm3+ (NYF) hexagonal micro-plates with efficient near-infrared (NIR)-to-NIR up-conversion (UC) via a new ion-exchange modified (IEM) hydrothermal method are reported. IEM not only significantly increases the UC intensity by up to 1000 times and prolongs the emission lifetimes of Tm3+ and Yb3+, but also enables the monodisp...

The demand for more efficient and complete sorting techniques for plastic waste is growing, and one possible solution isbased on fluorescent labeling. Novel fluorescent labels based on trivalent lanthanide (Ln3+) activated inorganic up-conversion (UC) materials offer a promising technological solution for plastic recycling. UC is a nonlinear, anti-...

We report efficient dual-mode up-conversion (UC) and down-shifting (DS) emission in a single Yb3+/Er3+-co-doped β-NaYF4 microcrystals with controlled morphology and size via a simple Na+ ion-exchange modification (IEM) method. IEM well preserves the crystal structure and monodispersed morphology of hydrothermal-synthesized β-NaYF4. Meanwhile, IEM g...

We develop an efficient green upconversion (UC) β-NaYF4:20%Yb³⁺,2%Er³⁺ microcrystal with well controlled morphology and size by hydrothermal method using two different chelating agents of CIT and EDTA-2Na via a simple ion-exchange reaction. Importantly, the UC emission efficiency of newly developed CIT and EDTA-2Na β-NaYF4:20%Yb³⁺,2%Er³⁺ microcryst...

We report on the photoluminescence (PL) properties of Eu-doped alkaline earth aluminoborate glasses MO-Al2O3-B2O3 (M=Ca, Sr and Ba) as visually transparent warm-white phosphors for near-UV excitation. Due to the high acidity of the aluminoborate matrix, Eu2+ can be readily stabilized to assume six- to eight-fold oxygen coordination. The energetic g...

We report on the magneto-optical (MO) properties of heavily Tb3+-doped GeO2-B2O3-Al2O3-Ga2O3 glasses towards fiber-integrated paramagnetic MO devices. For a Tb3+ ion concentration of up to 9.7×10^21 cm-3, the reported glass exhibits an absolute negative Faraday rotation of ~ 120 rad/T/m at 632.8 nm. The optimum spectral ratio between Verdet constan...

Intense photoluminescence was observed from mixed-valence Eu-doped nanocrystalline BaAl2Si2O8/LaBO3 glass ceramics. For preparation in air, the ratio between Eu3+ and Eu2+ luminescence depends on synthesis temperature. XRD, TEM and IR absorption spectra were employed to characterize the crystallization process and structural properties of the precu...

We report on the photoluminescence (PL) properties of heavily Eu2O3 doped Y2O3-Al2O3-B2O3 glasses as a high-gain red-emitting material for red photoconversion. A UV-to-red conversion efficiency of up to 60 % is achieved in this material. Concentration quenching is related to the formation of -{Eu-O-Me-O-Eu}- (Me = B, Y, Al) and -{Eu-O-Eu}- linkages...

We report on spectral modification through NIR down-conversion (DC) photoluminescence (PL) in Yb3+-Bi3+-co-doped Zn2GeO4. Energetic downshifting (DS) of UV-A irradiation occurs via intrinsic luminescence of the high-bandgap semiconductor Zn2GeO4 as well as via active Bi3+ centres. In parallel, both species act as sensitizers for Yb3+, strongly exte...

We report on photoluminescence from Eu³⁺-activated Na,Y-silicates of the Na3YSi3O9 type. The effect of structural environment on Eu³⁺-related emission is considered by comparing a glassy reference host to its crystalline correspondents which are obtained through crystallization of the super-cooled melt. Crystallization is accompanied by a quantitat...

We report on photoluminescence down-shifting and near-IR emission from Nd3 + centers in 50P2O5–(50-x)SrO–xMnO metaphosphate glasses. In those glasses, manganese exists predominantly in its divalent state with a Mn3 + fraction of less than 0.1 % of total Mn. The Mn2 + ions are octahedrally coordinated so that a broad red emission band is observed af...

We report on the photoluminescence of heavily Eu3+-doped SrO–La2O3–Al2O3–B2O3–SiO2 glasses. The specific glass system enables highly efficient photoemission for a dopant concentration of up to 8 mol% of Eu2O3 before concentration quenching is observed. This allows for the realization of high absorption cross section combined with an internal quantu...

We report on downconversion of one blue photon to two near-infrared (NIR) photons (~10000 cm⁻¹) in Pr³⁺/Yb³⁺ co-doped SrO-La2O3-Al2O3-B2O3-SiO2 glasses and LaBO3 glass ceramics. The Pr³⁺ ions act as broadband spectral sensitizer in the spectral range of 415-505 nm. Energy transfer occurs subsequently from Pr³⁺ to Yb³⁺, followed by re-emission in th...

We report on near-infrared (NIR) down-conversion by energy transfer between Mn2+ and Yb3+ in crystalline Zn1.96−xGeO4+1/2x:Mn0.04Ybx. In the Zn2GeO4 lattice, intrinsic defect transitions and Mn2+ ions act as broadband spectral sensitizers by absorbing UV-Vis (280–500 nm) photons and transferring the absorbed energy to Yb3+ centers in a cooperative...

Controlled collapse of a silicoaluminophosphate molecular sieve CHA-type SAPO-34 by thermal aging was studied in a multi-method approach. Structural changes and the mechanism of order–disorder–order transi-tions during collapse were followed for varying annealing conditions between 1000 and 1100 °C. Collapse of SAPO-34 occurs via the formation of a...

A novel erbium ion doped fluoro-tellurite glasses were prepared, and 2.7 μm emission properties, thermal stability and chemical durability were investigated. An intense 2.7 μm emission was observed. It was also found that the thermal stability and chemical durability were greatly improved by introducing a small amount of TeO2 into fluoride glasses....

Ultrabroad near-infrared (NIR) photoluminescence from Ni 2 + -centers in nanocrystalline Ba-Al titanate glass ceramics was studied by temperature-dependent static and dynamic photoluminescence spectroscopy in the regime of 10 to 300 K. Photoluminescence covers the spectral range of about 1100 nm to > 1600 nm with a typical bandwidth (FWHM) greater...

Nanocrystalline Ba–Al titanate precipitates from supercooled TiO2–BaO–SiO2–Al2O3 melts by catalyzed volume nucleation in the presence of Ni2+, forming a BaAl2Ti6O16 hollandite-type lattice. Ni2+-species are incorporated into the crystalline environment in octahedral coordination. Hollandite formation is accompanied by precipitation of tetrahedrally...

We report on photoluminescence of vanadium-doped lithium zinc silicate glasses and corresponding nanocrystalline Li2ZnSiO4 glass ceramics as broadband UV-to-VIS photoconverters. Depending on dopant concentration and synthesis conditions, VIS photoemission from [VO4]³⁻ is centered at 550-590 nm and occurs over a bandwidth (FWHM) of ~250 nm. The corr...

We report on the photoluminescence (PL) of Mn2+-doped (Li+, Zn2+) aluminosilicate glasses and glass ceramics. Glass ceramics are fabricated by controlled crystallization of as-melted precursor glasses. X-ray diffraction (XRD), electron spin resonance (ESR) and PL analyses indicate precipitation of Li4–2(x+y)ZnxMnySiO4, with relatively low x and y v...

We report on tunable photoluminescence from mixed-valence Eu-doped nanocrystalline Li2ZnSiO4 glass ceramics. After preparation of the precursor glass in air, gradual reduction of Eu3+ to Eu2+ occurs intrinsically during thermal annealing and precipitation of crystalline Li2ZnSiO4. Dual-mode photoemission can be generated for exciting at a wavelengt...

Intense photoluminescence was observed from mixed-valence Eu-doped nanocrystalline BaAl2Si2O8/LaBO3 glass ceramics. For preparation in air, the ratio between Eu³⁺ and Eu²⁺ luminescence depends on synthesis temperature. XRD, TEM and IR absorption spectra were employed to characterize the crystallization process and structural properties of the precu...

Glasses with composition 50Bi2O3–(50 − x) B2O3–xGeO2 (x = 0, 5, 10, 15 mol%) were prepared by conventional melting method. The thermal properties were investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refract...

53.3BiO1.5–33.3GeO2–13.4NaO0.5 (cation%) glasses with various Tm3+ concentration were prepared by melt-quenching method. These glasses show high density, high refractive index, low phonon energy and good stability against crystallization. Absorption spectra of Tm3+-doped bismuthate glass were measured to obtain the radiative lifetimes by Judd-Ofelt...

Oxyfluoride glasses, 30.9SiO2–15.5AlO1.5–30.9PbF2–22.7CdF2–1.5TmF3–xHoF3 (x=0.1,1,1.5x=0.1,1,1.5) (mol %), were prepared by traditional melt-quenching method. By appropriate heat treatment of the precursor glasses as described above, transparent glass ceramics were obtained with β- PbF2 nano-crystals embedded in glassy matrix as confirmed by X-ray...

Tm3+ and Ho3+ co-doped TeO2–ZnO–Bi2O3 (TZB) glasses were prepared by the conventional melt-quenching method. Two micrometre emission properties of the TZB glasses exited by 808 nm Laser Diode (LD) were analyzed and discussed. The Judd–Ofelt parameters, spontaneous radiative transition probabilities and radiative lifetime of Ho3+ were calculated bas...

The lead-free boron silicon bismuthate glasses were investigated in terms of their physical, optical and structural properties. The physical properties of these glasses have been explored by compositional variation of X-ray diffraction (XRD), differential thermal analysis (DTA) and density. The optical properties of theses glasses have been investi...

This paper reports 2.0 μm emission properties of Tm3+/Ho3+ co-doped oxyfluoride tellurite glass exited by 808 nm laser diode (LD). Mid-infrared transmittance property of glass was investigated by Fourier transform infrared (FTIR) spectrometer. The real chemical composition of investigated glass was identified by X-ray photoelectric spectroscopy (XP...

This work measured thermal stability, optical transmittance, nonlinear optical properties and supercontinuum generation of a novel TeO2-based glass and demonstrated its potential application in optical devices.

By investigating the second-harmonic generation (SHG) of the series (100−2x)GeS2·xGa2S3·xPbI2 (x=5, 10, 15, and 20) chalcohalide glass samples after thermal poling, it was found that there was an optimal poling temperature for each composition and there was also a relation between optimal poling temperature and glass transition temperature. With in...