The enhanced luminescences of Er3+/Yb3+ co-doped Y2Ti2O7 films were demonstrated when silver/gold (Ag/Au) nanoparticles (NPs) were doped in the films. With the precipitation of the Ag nanoprisms, more intense green (525 nm, 546 nm), red (659 nm) upconversion (UC) emission bands and strong enhanced near infrared (NIR) emission were observed and the enhanced factors were up to 16.7, 15.6, 17.7 and 5.6 folds, respectively. The accordance between the local surface plasmon resonance of NPs and the UC emission band significantly increased the luminescence intensity. The efficiencies of the radiative emissions were enhanced also due to the hydroxyl groups primarily absorbed around the NPs.Graphical abstractHighlights► The enhanced luminescences were demonstrated with silver/gold nanoparticles doping. ► The strong enhanced near infrared emission were observed. ► More intense upconversion emission bands were observed. ► Two mechanisms explained the reasons of the above enhanced emissions.

Re3+ (Re3+=Tm3+, Dy3+, Sm3+) ions doped phosphate glasses for white light emitting diodes (W-LEDs) are successfully prepared by the high-temperature melting method. The luminescence properties of the glasses were characterized by the emission and excitation spectra. When excited by ultraviolet light Tm3+ ions single doped, Dy3+ ions single doped, and Sm3+ ions single doped phosphate glass emit blue, green and red light, which give the characteristic transitions of Tm3+ ions (1D2→3F4), Dy3+ ions (4F9/2→6H13/2,15/2), and Sm3+ ions (4G5/2→6H7/2,9/2), respectively. Moreover, there exists simultaneous luminescence of Tm3+, Dy3+, Sm3+ ions individually when co-doping them in the single phased phosphate glass (for example, Tm3+/Sm3+ ions co-doped; Dy3+/Sm3+ ions co-doped; Dy3+/Tm3+ ions co-doped; Tm3+/Dy3+/Sm3+ ions tri-doped systems), which is beneficial to tune the emission colors. Under the 360 nm excitation, the CIE coordinates of Tm3+/Dy3+/Sm3+ ions tri-doped samples are close to the standard equal energy white light illumination (x=0.333, y−0.333). With an increasing in Sm3+ ions concentration, blue and green emissions decrease gradually while red emission increases. In addition, the energy transitions among Tm3+, Dy3+, and Sm3+ ions are discussed in detail. The phenomenon is reasonably interpreted based on the analysis of the luminescence lifetime.

By solid-state synthesis method, Ho3+/Yb3+ co-doped CeO2–ZrO2 nano-powders have been prepared. The concentration of Ce4+ ions has greater effect to the oxygen lattice structure. When the concentration of Ce4+ ions is 30 mol%, the oxygen lattice is a tetrahedral space group and the luminescence intensity of the sample is strongest. The results show that the lattice structure can be changed by inducting the Ce4+ ions into Ho3+/Yb3+ co-doped ZrO2. And the emission character can be improved.Highlights► The lattice of ZrO2 can be changed by introducing Ce4+ ions. ► The up-conversion emission of the material is improved by changing the concentration of Ce4+ ions. ► The low phonon energy of the material is very helpful to the up-conversion emission.

The Er3+/Yb3+ co-doped Y2Ti2O7 phosphors were synthesized by the sol–gel method. XRD, TEM, and photoluminescence spectra of samples were measured and studied. The results demonstrate that the Y2Ti2O7 would transform from the amorphous to nanocrystalline at about 750 °C. The mechanism of both upconversion and near infrared (NIR) photoluminescence and their changes with annealing temperature were analyzed. What is more, the pump-saturation effect of NIR emission and the anomalous slopes of the fitted straight line in the double-logarithmic plots for upconversion emissions were found in the nanocrystalline samples, which can be ascribed to domination of upconversion over linear decay for the 4I11/2 and 4I13/2 state and the saturation of 4I13/2 state in Er3+ ions largely owing to the energy back-transfer process. They are induced by high pump power and Yb3+ ions concentration.Highlights► Pump-saturation of NIR photoluminescence. ► Anomalous slope (less than 1) of the fitted straight line in the double-logarithmic plots for up-conversion emissions. ► We proved the energy back transition(EBT) process and the non-radiative multiphonon relaxation from 2H11/2 and 4S3/2 levels. ► We analyzed the change of PL intensity with annealing temperature. ► The transition from the amorphous to the nanocrystallines.

By conventional high-temperature melting method, Yb3+/Er3+/Tm3+ co-doped phosphate glass was synthesized. After annealing the precursor glass, the phosphate glass ceramic (GC) was obtained. By measuring the X-ray diffraction (XRD) spectrum, it is proved that the LiYbP4O12 and Li6P6O18 nano-crystals have existed in the phosphate GC. The up-conversion (UC) emission intensity of the GC is obvious stronger compared to that of the glass. The reason is that the shorter distance between rare earth ions in the glass ceramic increases the energy transitions from the sensitized ions (Yb3+) to the luminous ions (Er3+ and Tm3+). By studying the dependence of UC emissions on the pump power, the 523 and 546 nm green emissions of Er3+ ions in the glass are two-photon processes. But in the glass ceramic, they are two/three-photon processes. The phenomenon implies that a three-photon process has participated in the population of the two green emissions. Using Dexter theory, we discuss the energy transitions of Er3+ and Tm3+. The results indicate the energy transition of Tm3+ to Er3+ is very strong in the GC, which changes the population mechanism of UC emissions of Er3+.

We prepared Er3+ doped and Er3+/Yb3+ codoped Sb2O4 nanocrystals by the sol–gel method. The Raman, X-ray diffraction (XRD), transmission electron microscope (TEM), and photoluminescence spectra of the samples were studied. The phonon energy of the Sb2O4 nanocrystals is very low (the maximum value being 461 cm−1). The upconversion (UC) red emission of the Er3+/Yb3+ codoped sample is very strong at 975 nm laser diode excitation. The Sb2O4 nanocrystals will be a promising luminous material.

The significant enhancement of luminescence of the europium (Eu) complex Eu(TTFA)3 owing to the local surface plasmon resonance (LSPR) of the silver nanocubes was observed. The excitation and emission enhancements were both presented. The excitation enhancement mainly came from the balance of two aspects. Besides the spectra overlap between the LSPR spectrum and the excitation bands of Eu ions, the intrinsic intensity of the excitation of the Eu ions in absence of nanocubes also played an important role. The emission enhancement, which was the relative change in the radiative decay rate, non-radiative decay rate and quantum efficiency, of the Eu ions at 612 nm came from the change of the photonic mode density (PMD) and was concerned with concentrations of the nanocubes as well as the excitation wavelengths.

For developing the white-light-emitting (WLE) material, we prepared Tm3+/Tb3+/Mn2+ tri-doped phosphate glass and glass ceramic samples. At 360 nm ultraviolet light excitation, the colors of the luminescence of the glass and glass ceramic samples are white. The CIE chromaticity coordinates (X = 0.324, Y = 0.335) of the emission from the glass ceramic are close to the standard white-light illumination (0.333, 0.333). The intensity of the fluorescence in the glass ceramic is approximately 20 times stronger than that in the glass.Highlights► We prepare Tm3+/Tb3+/Mn4+ tri-doped phosphate glass ceramic which own low cost and high efficiency. ► The material can emit strong white-light at 360 nm ultraviolet light excitation. ► The CIE chromaticity coordinate of the emission from the glass ceramic is (X = 0.324, Y = 0.335).

The up-conversion (UC) and near infrared (NIR) luminescence of Er3+/Yb3+ co-doped phosphate glass are investigated. In the UC emission range, the 523 nm, 546 nm green emissions and the 659 nm red emission are observed. With the increasing pump power, the intensity ratios of I523/I659, I546/I659 and I523/I546 increase gradually. The phenomenon is reasonably interpreted by theoretical analysis based on steady state rate equations. The emission cross section of the infrared emission at 1546 nm is larger (about 6.7 × 10− 21 cm2), which is suitable for making fiber amplifier.Research Highlights► The intensity ratios of the upconversion emissions in the Er3+/Yb3+ co-doped P2O5-CaO-Na2O- Al2O3-AgO phosphate glass can vary with the pump powers. ► Based on steady state rate equations, the phenomenon that the intensity ratios of the upconversion emissions vary with the pump powers is reasonable interpreted. ► This research will be helpful to developing the luminescence materials, like as fluorescence anti-counterfeiting and color display.

The Er3+/Yb3+ co-doped phosphate glass was prepared by high temperature fusing method. The up-conversion (UC) emission of the sample was measured at 975 nm laser diode (LD) excitation. Using the ratio of the integral intensity of the UC green emission to that of the UC red emission at different pump powers, we calculated the energy transition (ET) coefficient of Yb3+ to Er3+.

The effect of temperature on the luminescence intensity of up-conversion and near infrared in Er3+/Yb3+ co-doped phosphate glass ceramics has been investigated. Efficient green and red up-conversion luminescence and strong infrared fluorescence at 1.54 μm wavelength are observed under excitation of 975 nm. The fluorescence intensity is changing at different temperature and the results are explained with the level transitions in Er3+/Yb3+ co-doped system. Meanwhile, the lifetime of Er3+:4I13/2 level corresponding to different operating temperature and pump power is also discussed, and the experimental results are fitted using multiphonon relaxation theory.

We have prepared Er3+/Yb3+ co-doped transparent phosphate glass ceramics by the high-temperature melting technique, and demonstrated the influence of energy acceptors Ce3+ ions on the up-conversion and 1.54 μm emission properties of Er3+. The energy transfer mechanism is discussed based on the energy matching and the energy level structure. The phonon-assisted energy transfer between Er3+ and Ce3+ favors population feeding from the 4I11/2 to the 4I13/2 level, and therefore drastically decreases the up-conversion emission intensity of Er3+. Meanwhile, 1.54 μm fluorescence enhances greatly with the introduction of Ce3+ ions at the proper concentration.

Using Czochralski (CZ) pulling method, an Er3+/Yb3+-codoped NaY(WO4)2 crystal was prepared. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Some optical parameters, such as intensity parameters, spontaneous emission probabilities and lifetimes, were calculated from absorption spectra with Judd–Ofelt (J–O) theory. Upconversion luminescence excited by a 970 nm diode laser was studied. In this crystal, green upconversion luminescence is particularly intensive. Energy transfer mechanisms that play an important role in upconversion processes were analyzed. Two cross-relaxation processes: 4G11/2 + 4I9/2 → 2H11/2 (or 4S3/2) + 2H11/2 (or 4S3/2), and 4G11/2 + 4I15/2 → 2H11/2 (or 4S3/2) + 2I13/2, which contribute to the intensive green luminescence under 378 nm excitation, were put forward. Background energy transfer 4G11/2(Er3+) + 2F7/2(Yb3+) → 4F9/2(Er3+) + 2F5/2(Yb3+) was also demonstrated.

The Er3+/Yb3+ co-doped Y2Ti2O7 phosphors were synthesized by the sol–gel method. XRD, TEM, and photoluminescence spectra of samples were measured and studied. The results demonstrate that the Y2Ti2O7 would transform from the amorphous to nanocrystalline at about 750 °C. The mechanism of both upconversion and near infrared (NIR) photoluminescence and their changes with annealing temperature were analyzed. What is more, the pump-saturation effect of NIR emission and the anomalous slopes of the fitted straight line in the double-logarithmic plots for upconversion emissions were found in the nanocrystalline samples, which can be ascribed to domination of upconversion over linear decay for the 4I11/2 and 4I13/2 state and the saturation of 4I13/2 state in Er3+ ions largely owing to the energy back-transfer process. They are induced by high pump power and Yb3+ ions concentration.Highlights► Pump-saturation of NIR photoluminescence. ► Anomalous slope (less than 1) of the fitted straight line in the double-logarithmic plots for up-conversion emissions. ► We proved the energy back transition(EBT) process and the non-radiative multiphonon relaxation from 2H11/2 and 4S3/2 levels. ► We analyzed the change of PL intensity with annealing temperature. ► The transition from the amorphous to the nanocrystallines.