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Double wavelength emitting phosphors with hypersensitive thermal response are important for optical/thermal sensors and multiplexing optical data storage technology. However, it is a daunting challenge to develop multicolor electron‐trapping materials with superheat sensitivity and anomalous quenching luminescence characteristics for information storage. Here, based on the selection of host lattice and the control of doping ion types, we have designed Mn2+‐ and/or Cr3+‐activated persistent materials with excellent fluorescence properties. Among these phosphors, Mn,Cr co‐activated biphasic mixture exhibits not only sensitive anomalous thermosensitive fluorescence properties but also multicolor and multimode fluorescence emission characteristics derived from Mn and Cr simultaneously. The corresponding multimode fluorescence mechanism is proposed based on afterglow energy transfer and deepening trap effect. Especially, based on the excellent fluorescence performances, these phosphors as information storage medium demonstrate multilevel information storage by a combination of the trap multiplexing and wavelength multiplexing technologies. The study here provides not only the ideas for designing and synthesizing new electronic materials but also a material foundation for the fourth generation of optical information storage and encryption. [ABSTRACT FROM AUTHOR]

Light with wavelength longer than 1500 nm has great potential to afford deep bio‐tissue penetration due to its extremely weak photon scattering and undetectable autofluorescence in vivo. Here, in order to satisfy the requirements for thermometry during the tumor hyperthermia process, an ultrasensitive optical thermometer operating beyond 1500 nm is developed by employing the thermally coupled Stark sublevels of Er3+: 4I13/2 → 4I15/2 transition based on fluorescence intensity ratio (FIR) technology in Yb3+ and Er3+ codoped BaY2O4. Compared with the typical upconversion (UC) material β‐NaYF4: Yb3+/Er3+ and Y2O3: Yb3+/Er3+, BaY2O4: Yb3+/Er3+ shows more intense red Er3+: 4F9/2 → 4I15/2 transition and 1.5 μm near‐infrared (NIR) Er3+: 4I13/2 → 4I15/2 transition induced by its larger phonon energy and higher quenching concentration of Er3+. An equivalent four‐level model is proposed to investigate the temperature characteristics of the NIR emission, from which four Stark transitions are separated from the raw spectra, named α, β, γ, and δ respectively. Then, the NIR thermal sensing performance have been developed by utilizing the FIR of Iβ to Iα and Iγ to Iα. More importantly, an ultra‐high sensitivity for optical thermometry has been obtained through the combination of transition β and γ, especially in the physiological temperature region. Furthermore, the detection depth of NIR light in bio‐tissues is assessed by an ex vivo test, demonstrating that the maximal detection depth of NIR emission can reach to 8 mm without any influence on optical thermometry. These findings indicate that Yb3+ and Er3+ codoped BaY2O4 is a remarkable contender for optical thermometry in deep tissue with ultra‐high sensitivity. [ABSTRACT FROM AUTHOR]

Nanocrystal Y2O3 powders with different grain sizes and various doping concentrations of Tb3+ were prepared by an autocombustion reaction. The size and surface effects on the 4f-5d transitions and energy transfers between Tb3+ ions were studied by using x-ray diffraction, transmission electron microscopy, fluorescent spectra, and luminescent decay. It was found that the excitation spectra are composed of two parts: one is the contribution from the Tb3+ at/near the nanoparticle surfaces; another is from the Tb3+ inside the nanoparticles. The study on the concentration quenching and luminescent decay indicated that the energy transfers depopulating the 5D3 and 5D4 level were assigned to the mechanisms of electric dipole-dipole and exchange interaction, respectively. The size confinement greatly affects the energy transfer quenching the emission from the 5D3 level, but slightly affects the energy transfer quenching the emission from the 5D4 level. [ABSTRACT FROM AUTHOR]

The luminescent properties of concentration dependence are reported in BaMg2Si2O7:Eu2+,Mn2+ red phosphor. It is observed that the broad red emission of Mn2+ consists of two bands, located at 620 and 675 nm, respectively, which are attributed to two different Mn2+ centers [Mn2+(I) and Mn2+(II)] substituting for two nonidentical Mg2+ sites [Mg2+(I) and Mg2+(II)] in the host. It is also found that the relative emission intensity of the Mn2+(II) to the Mn2+(I) increases with increasing Mn2+ concentration, leading to a red-shift of the overall emission. A detail analysis on the energy transfer from Eu2+ to the two Mn2+ centers is presented, which indicates that the number ratio of Mn2+(II) to Mn2+(I) increases with increasing Mn2+ concentration. This result is interpreted by the preferential formation of Mn2+(I) substituting for Mg2+(I) site. Based on energy transfer, the emission intensity ratios of Mn2+(I) to Eu2+ and Mn2+(II) to Eu2+, which is Mn2+ concentration dependent, are calculated using related fluorescence lifetimes. The calculated results are in good agreement with that obtained experimentally in the emission spectra. [ABSTRACT FROM AUTHOR]

This study shows that alizarin red (AR) only slightly quenched fluorescence for acridine orange (AO) in an AR/AO mixed solution at pH = 5–6. The reduced fluorescent signal was closely and linearly associated with the level of MT added to the system, which is the basis for a new quantitative MT assay method using the fluorescence quenching reaction in the AO–AR system. The results show that under optimal conditions, this method had a 14.9–43.5 mg L −1 linear detection range with a 1.38 mg L −1 detection limit and 1.24% precision. In addition, this method was used to determine the MT levels in the commercially available MT-containing pesticides and suppositories, which showed a 96.6–103% recovery. Therefore, this method has multiple advantages, including simple and fast operation, high accuracy and low cost. Moreover, herein, we investigated the underlying mechanism in-depth using an ultraviolet (UV) spectroscopic technique. [ABSTRACT FROM AUTHOR]

Highlights: [•] Eu2+ and Mn2+ codoped SrSi2O2N2 phosphors were first synthesized by sol–gel method. [•] The green emission of Eu2+ was greatly enhanced by codoping Mn2+ ions. [•] The reason is attributed to the coexcitation and energy transfer from Mn2+ to Eu2+. [•] SrSi2O2N2: Eu2+, Mn2+ also exhibits a higher quantum yield and better thermal stability. [•] SrSi2O2N2:Eu2+, Mn2+ is a promising green-emitting phosphor for WLEDs. [ABSTRACT FROM AUTHOR]

A multiphase strategy is proposed and successfully applied to make the insulating green phosphor CaCeAl3O7:Tb3+ conductive in the form of 12CaO·7Al2O3–CaCeAl3O7:Ce3+,Tb3+. The phosphor shows bright green-light emission with a short lifetime (2.51 ms) under low-voltage electron beam excitation (3 kV). The green photo- and cathodoluminescence from 5D4–7FJ (J = 6, 5, 4, 3) transitions of Tb3+ are significantly enhanced in comparison with pure C12A7:Tb3+. It was confirmed that this enhancement is the consequence of the joint effects of energy transfer from Ce3+ to Tb3+ and broadening of the absorption spectrum of Ce3+ due to the existence of multiple phases. In particular, under 800 V electron beam excitation, cathodoluminescence is improved by the modified electrical conductivity of the phosphor. When compared to the commercial Zn2SiO4:Mn2+ with a long luminescence lifetime of 11.9 ms, this conductive green phosphor has greater advantage for fast displays. [ABSTRACT FROM AUTHOR]

Abstract: Pulsed discharge system has been drawn extensive attentions for harmful gas removal, while the ·OH radicals play ssential role during the removal reactions. In order to clarify the ·OH radical generation process, a zero dimensional numerical model has been established for the N2/H2O System in negative pulsed streamer discharge instrument. The model is verified based on comparison between the simulated and the experimentally detected time-resolved fluorescence of ·OH(A2∑+) radicals. The concentration variance of H2O and N2 versus time implies that the N2 molecules exhaust major part of the injecting energy during discharge, and the main path to produce ·OH radicals include the excited ·OH(A2∑+) formation in pulse discharge and the ·OH(X2II) formation by energy transfer from excited N2 to the H2O molecules after pulse discharge. The concentration of N2 is the critical factor to manipulate the ·OH(A2∑+) production dynamic, presented as the decrease of N2 initial proportion heightening the production concentration of ·OH(A2∑+), while the generation dynamic more delayed. [Copyright &y& Elsevier]

Abstract: We have successfully synthesized Eu3+-doped TbPO4 nanowires, which are orderly organized to form bundle-like structure. A thermal treatment up to 600°C does not modify the size, shape and structure of as-synthesized sample. Due to the energy overlap between Tb3+ and Eu3+, an efficient energy transfer occurs from Tb3+ to Eu3+. The effects of Eu3+ concentration and thermal treatment on the luminescent properties of Eu3+ are investigated. The increase of Eu3+ concentration leads to the increase of the energy transfer efficiency from Tb3+ to Eu3+, but also enhances the probability of the interaction between neighboring Eu3+, which results in the concentration quenching. With the heat-treatment, the luminescence of Eu3+ presents an obvious increase, but almost no change for the luminescence of Tb3+. This difference is explained based on the TGA, DTA, and fluorescent decay dynamics analyses. [Copyright &y& Elsevier]

High-performance optical thermometer that can operate in the long-wavelength range of the second near infrared (1500 nm–1700 nm, NIR-IIb) biological window is in desperate need for bio-medical treatment. In this paper, a multipath temperature sensor Y 3 NbO 7 : Yb3+/Er3+ with pure cubic phase is synthesized by the high temperature solid state method. Under the excitation of 980 nm wavelength, efficient green upconversion emission attributed to thermally coupled Er3+: 2H 11/2 /4S 3/2 levels are found, through which an excellent temperature sensing properties are realized with the maximal absolute and relative sensitivity of approximately 0.54 % K −1 and 1.37 % K −1 as well as the minimal temperature resolution of about 0.024 K. More importantly, the sample exhibits remarkable temperature detection capacity in deep tissues, which is implemented by the thermally coupled Stark sublevels of Er3+: 4I 13/2 locating just in the NIR-IIb sub-window. Thanks to this appropriate response wavelength range, the maximal penetration depth of the NIR-IIb optical thermometer in the biological tissues can reach up to 8 mm. All the findings indicate that the present sample is a supernormal multipath thermometric probe with detectability in the deep biological tissues. [ABSTRACT FROM AUTHOR]

Non-invasive photothermal therapy (PTT) is proposed as a powerful method for cancer treatment, in which a precise temperature monitoring is strongly recommended during the photothermal conversion process to prevent the damage of normal cells. Herein, ultra-sensitive optical thermometry with excellent resolution and outstanding light-to-heat conversion are simultaneously realized in CaSc 2 O 4 : Yb3+/Nd3+ nanorods. The temperature sensing of the nanorods is accomplished through fluorescence intensity ratio (FIR) technology based on the thermally coupled levels (TCLs) Nd3+: 4F j (j = 7/2, 5/2, 3/2), of which the obtained absolute sensitivity is about 6.5 times larger than the optimal value of TCLs-based thermometers reported previously. Meanwhile, an intense thermal enhancement of Nd3+: 4F j (j = 7/2, 5/2, 3/2) → 4I 9/2 transition is found due to the efficiency improvement of phonon-assisted energy transfer process between Yb3+ ions and Nd3+ ions. The penetrability of the near-infrared light emitting by Nd3+ ions is determined by a simple ex vivo experiment, indicating a penetration depth of 8 mm in the biological tissues with negligible effect on FIR values. Beyond that, the nanorods show remarkable photothermal conversion capacity under the excitation of 980 nm wavelength. The properties mentioned above show enormous potentiality of the present nanorods for PTT along with a real-time temperature sensing. [ABSTRACT FROM AUTHOR]

Abstract: Tb3+/Dy3+ and Eu3+/Sm3+ doped rare-earth borate glasses have been synthesized and characterized. Under UV excitation, Dy3+, Tb3+, Sm3+ and Eu3+ emit intense yellowish white, green, reddish orange and red lights, respectively. In Tb3+/Dy3+ co-doped glasses, the enhancement of Tb3+ green emission is observed, and the sensitization is related to the efficient energy transfer from Dy3+ to Tb3+. In Eu3+/Sm3+ co-doped glasses, the excitation wavelength range of Eu3+ emission is broadened owing to the energy transfer from Sm3+ to Eu3+. This broadening makes the Ar+ 488nm wavelength laser a powerful excitation source for Eu3+ fluorescence. The rare-earth doped glasses with various visible emissions are useful for developing new color light sources, fluorescent display devices, UV-sensor and tunable visible lasers. [Copyright &y& Elsevier]

The luminescent properties of concentration dependence are reported in BaMg2Si2O7:Eu2+,Mn2+ red phosphor. It is observed that the broad red emission of Mn2+ consists of two bands, located at 620 and 675 nm, respectively, which are attributed to two different Mn2+ centers [Mn2+(I) and Mn2+(II)] substituting for two nonidentical Mg2+ sites [Mg2+(I) and Mg2+(II)] in the host. It is also found that the relative emission intensity of the Mn2+(II) to the Mn2+(I) increases with increasing Mn2+ concentration, leading to a red-shift of the overall emission. A detail analysis on the energy transfer from Eu2+ to the two Mn2+ centers is presented, which indicates that the number ratio of Mn2+(II) to Mn2+(I) increases with increasing Mn2+ concentration. This result is interpreted by the preferential formation of Mn2+(I) substituting for Mg2+(I) site. Based on energy transfer, the emission intensity ratios of Mn2+(I) to Eu2+ and Mn2+(II) to Eu2+, which is Mn2+ concentration dependent, are calculated using related fluorescence lifetimes. The calculated results are in good agreement with that obtained experimentally in the emission spectra. [ABSTRACT FROM AUTHOR]

A series green emission phosphors Sr 3 Lu 2 (BO 3) 4 :Ce3+,Tb3+ (denoted as SLBO:Ce3+,Tb3+) with broad absorption band matching well with UV LED chip were synthesized by the solid–state reaction method. The phase and structure were analyzed with XRD, EDX, FT-IR measurements. The energy transfer between Ce3+ and Tb3+ in SLBO was proved by spectra and decay curves detailedly. The emission colors vary from blue to green by adjusting the ratio of Ce3+/Tb3+ doped concentration. With temperature increasing, SLBO:Ce3+,Tb3+ phosphor shows well thermal stability that emission intensity retains 70% of its initial at 25 °C even temperature rising to 150 °C. The internal and external quantum efficiency of SLBO:3%Ce3+,8%Tb3+ are 77.5% and 34.8% under 340 nm excitation, respectively. Combining the as-synthesized SLBO:Ce3+,Tb3+ and red emission phosphor CaAlSiN 3 :Eu2+ coated on a 365 nm UV chip, a warm white LEDs device with CRI of 83 was achieved. All the results indicate that the SLBO:Ce3+,Tb3+ phosphor has potential application in UV pumped white LEDs. • Green emission Sr 3 Lu 2 (BO 3) 4 :Ce3+,Tb3+ for UV LED chip were synthesized. • Energy transfer of Ce3+-Tb3+ in Sr 3 Lu 2 (BO 3) 4 was proved. • Warm white LEDs device with CRI of 83 was achieved. [ABSTRACT FROM AUTHOR]

Pr 3+ /Yb 3+ codoped CaGdAlO 4 (CGA) quantum cutting phosphors were synthesized by a self-propagating combustion method along with a subsequent heat treatment. For these phosphors, a deep ultraviolet (DUV) to near infrared (NIR) quantum cutting via the energy transfer from Pr 3+ to Yb 3+ ions has been realized under the 4f-5d excitation of Pr 3+ when its 5d level is lower than the 1 S 0 . It can be found that the cascade relaxation processes of the electrons from the excited 4f5d state to the 3 P 0 state play a key role in obtaining the 4f-4f emissions of Pr 3+ . In addition, at the optimal Yb 3+ concentration (6%), the most efficient DUV to NIR quantum cutting can be reached through the dominating two-step energy transfer from Pr 3+ to Yb 3+ upon DUV excitation ranging from 235 to 285 nm and the quantum cutting efficiency, η QCE , of the phosphor is ∼166%. Strikingly, the temperature-dependent NIR emission spectra suggest that these quantum cutting phosphors, having a higher thermal activation energy of 320 meV, exhibit a good thermal stability. Meanwhile, it is found that the existence of the DUV to NIR quantum cutting gives the phosphor a high resistance to UV irradiation. Our results indicate that Pr 3+ /Yb 3+ codoped CGA quantum cutting phosphors can be a candidate serving as a protective layer for silicon space solar cells. [ABSTRACT FROM AUTHOR]

Abstract: Expanded emission spectra ranging from green to red are reported in Ca3Sc2Si3O12 (CSS):Ce3+,Mn2+ silicate garnets. Mn2+ may occupy Ca2+ site (Mn2+(I)) to generate a yellow emission band at 574nm or Sc3+ site (Mn2+(II)) with red emission band at 680nm. Efficient energy transfers from the green emitting Ce3+ to both Mn2+(I) and Mn2+(II) occur upon blue excitation into Ce3+. Concentration dependence of Mn2+ emission is analyzed based on Ce3+–Mn2+ energy transfer, steady state rate equations, and fluorescence lifetimes. Energy transfer efficiency (η T) and rate (W) are calculated with values as high as 45% and 14.01×106 s−1, respectively. [Copyright &y& Elsevier]

Abstract: BaMg2Al6Si9O30:Eu2+ phosphors are synthesized by the solid-state reaction method and their photoluminescence (PL) properties are investigated. The ultraviolet emission originates from Eu2+(I) substituting for Ba2+ sites, whereas the blue emission is attributed to Eu2+(II) substituting for Mg2+ sites. With increasing Eu2+ doping concentrations, the blue emission band shifts to long wavelength and the PL intensity ratio of blue to ultraviolet emission increases. Energy transfer between the two different Eu2+ ions is analyzed by photoluminescence excitation and emission spectra, and lifetimes. Results indicate that the emission spectra can be tuned by changing Eu2+ contents. We have also demonstrated that BaMg2Al6Si9O30:Eu2+ phosphor is a kind of potential phosphor for fluorescent lamps. [Copyright &y& Elsevier]

Abstract: Luminescence properties of the yellow-emitting (Ca2Lu1−x Ce x )(ScMg)Si3O12 (CLSM:xCe3+ x =0.01–0.15) phosphor are investigated for various Ce3+ concentrations. Different Ce3+ emission sites and energy transfers between them are observed, resulting in a red shift of the emission spectra from 530 to 575nm with increasing x from 0.01 to 0.15. Combining with blue (460nm) InGaN LEDs, CLSM:Ce3+ shows excellent performances for phosphor-converted white LEDs with higher color rendering index R a of 87.4–87.9 and lower color temperature T C of 5034–5814K, especially for warm pcWLEDs with a high color rendering (R a >80) and a low color temperature (T C <4000K). Thermal quenching behaviors depending on Ce3+ concentrations and temperatures are discussed. [Copyright &y& Elsevier]

Abstract: Eu2+ and Eu2+–Mn2+ codoped (Ba,Sr)Mg2Al6Si9O30 phosphors have been synthesized by solid state reaction, and their luminescent properties are investigated. Under the excitation of 330nm, it is observed that the emission of Eu2+ consists of two emission bands, located at around 370 and 450nm, which are attributed to two Eu2+ centers (Eu2+(I) and Eu2+(II)) ions substituting for two different Ba2+ and Mg2+ sites, respectively. As Sr2+ gradually substitutes Ba2+, the emission bands of Eu2+(I) shift to longer wavelength whereas the emission bands of Eu2+(II) exhibit no change. This phenomenon is discussed in terms of the crystal-field strength. A detail analysis on the energy transfer from Eu2+ to Mn2+ in SrMg2Al6Si9O30 host is presented, which indicates the energy of the red emission of Mn2+ is derived mainly from Eu2+(I). We have also demonstrated that BaMg2Al6Si9O30:Eu2+, Mn2+ exhibits better thermal quenching properties than that of SrMg2Al6Si9O30:Eu2+, Mn2+ because of bigger activation energy. [Copyright &y& Elsevier]

Abstract: Eu2+ and Mn2+ co-doped Ca8Zn(SiO4)4Cl2 phosphors have been synthesized by a high temperature solid state reaction. Energy transfer from Eu2+ to Mn2+ is observed. The emission spectra of the phosphors show a green band at 505nm of Eu2+ and a yellow band at 550nm of Mn2+. The excitation spectra corresponding to 4f7-4f65d transition of Eu2+ cover the spectral range of 370–470nm, well matching UV and/or blue LEDs. The shortening of fluorescent lifetimes of Eu2+ followed by simultaneous increase of fluorescent intensity of Mn2+ with increasing Mn2+ concentrations is studied based on energy transfer. Upon blue light excitation the present phosphor can emit intense green/yellow in comparison with other chlorosilicate phosphors such as Eu2+ and Mn2+ co-doped Ca8Mg(SiO4)4Cl2 and Ca3SiO4Cl2, demonstrating a potential application in phosphor converted white LEDs. [Copyright &y& Elsevier]

Abstract: Upon 4K11/2 excitation of Sm3+ at 405nm, the performance of energy transfer from Sm3+ to Eu3+ in the red emitting phosphor CaMoO4:Eu3+, Sm3+ significantly extends its excitation region for better matching the near-UV LED. Photoluminescence spectra indicate that the energy transfer pathway concerns the relaxation from 4K11/2 to 4G5/2 of Sm3+ and subsequent transfer to 5D0 of Eu3+ rather than 5D1 of Eu3+. The fluorescent decay pattern of Sm3+ 4G5/2 level in CaMoO4:0.5% Sm3+, 2% Eu3+ is studied at 77K based on the Inokuti–Hirayama formula, revealing an electronic dipole–dipole interaction between Sm3+ and Eu3+. The coefficient for the energy transfer is obtained to be 8.5×10−40 s−1 cm6. The fluorescence rise and decay pattern of Eu3+ 5D0 level as Sm3+ is only excited at 77K is well described by the dynamical processes of the energy transfer. [Copyright &y& Elsevier]

Abstract: A series of Eu2+ and Mn2+ coactivated Ca3Al2(SiO4)3− δ Cl4 δ phosphors have been synthesized by solid state reactions and their luminescence properties have been investigated by means of powder diffuse reflection, photoluminescence excitation and emission spectra, and lifetimes. The phosphor Ca3Al2(SiO4)3− δ Cl4 δ :Eu2+, Mn2+ exhibits two dominating bands situated at 460 and 550nm, originate from the allowed 5d → 4f transition of the Eu2+ ion and the 4T1g(4G) → 6A1g(6S) transition of the Mn2+ ion, respectively. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the decline of lifetimes of Eu2+. By utilizing the principle of energy transfer, we have demonstrated that with appropriate tuning of activator content Ca3Al2(SiO4)3− δ Cl4 δ :Eu2+, Mn2+ phosphors exhibit potential to act as a phosphor for near ultraviolet light-emitting diodes. [Copyright &y& Elsevier]

Abstract: We report an intense full-color emission originating from 5D0,1,2,3 to 7F0,1,2,3,4 transitions of Eu3+ in CaSc2O4 upon 395nm excitation. The emission spectra vary with increasing Eu3+ concentration, demonstrating tunable color coordinates from white to red region in the CIE chromaticity diagram. Considering the relaxation from 5D J to 5D J −1 through cross energy transfer, the Eu3+ concentration dependent emission spectra are well simulated based on the analysis of steady state rate equations and the measured lifetimes of the 5D J levels. It is suggested that CaSc2O4:Eu3+ could be a potential single-phased full-color emitting phosphor for near-ultraviolet InGaN chip pumped white light emitting diodes. [ABSTRACT FROM AUTHOR]

Abstract: CePO4:Tb nanorods were synthesized via a simple wet-chemical route. The as-synthesized CePO4:Tb nanorods present high photoluminescence efficiency due to an efficient energy transfer form Ce3+ to Tb3+. However, heat treatment at 150°C in air leads to a significant decrease of photoluminescence. X-ray photoelectron spectroscopy and excitation spectra revealed the oxidation of Ce3+ to Ce4+ in the heat-treatment process, which should be responsible for significant photoluminescence degradation due to the breakage of Ce3+→Tb3+ energy transfer. This conclusion is further supported by atmosphere and size effects of photoluminescence of CePO4:Tb under the heat treatment. [Copyright &y& Elsevier]

Abstract: With the help of the Dexter''s theory, the energy transfer mechanism from Pr3+ 1S0 to Cr3+ is investigated theoretically in SrAl12O19:Pr3+, Cr3+ quantum cutting phosphors. The electron spin resonance (ESR) spectra of Pr3+ and Cr3+-doped SrAl12O19 with magnetoplumbite structure have been studied. The Cr3+ ion is found to enter the Al4(4f) site, which is very close to the Sr(2d) site replaced by the Pr3+ ions in the host. The theoretical results indicate that the efficient Pr3+ 1S0→Cr3+ energy transfer can only take place in the intermediate mirror planes, in which for the nearest and next-nearest Pr3+–Cr3+ pairs, both dipole–dipole and dipole–quadrupole interactions can play their parts in the transfer. Finally, an overview is given about the research on the energy transfer from Pr3+ 1S0 to codopants in their co-doped materials. [Copyright &y& Elsevier]

Abstract: α- and β-Ca2P2O7:Eu2+, Mn2+ phosphors were prepared by solid-state reaction. Phase transition from tetragonal (β-phase) to monoclinic (α-phase) is performed. A strong orange emission of Mn2+ is observed in both α-and β-Ca2P2O7:Eu2+, Mn2+ upon near ultraviolet (UV) excitation through energy transfer from Eu2+ to Mn2+. The transfer efficiencies for various Mn2+ concentrations are estimated based on lifetime measurements of the fluorescence of Eu2+ in the two phases. The photoluminescence excitation spectra of α-Ca2P2O7:Eu2+, Mn2+ can cover 400nm of the near-UV range, denoting its potential use as a phosphor with intense orange component for white light emitting diodes (LEDs). [Copyright &y& Elsevier]

Abstract: The energy transfer processes in Pr3+- and Cr3+-codoped SrAl12O19 system are studied experimentally. The transfer can convert the 1S0 ultraviolet fluorescence of Pr3+ into the red emission of Cr3+. The 3P0 state, which may be populated by 1S0→1I6 emission, can also act as a donor state in the transfer to Cr3+. Cross-relaxation process is reported firstly in energy transfer between the pair of Pr3+–Cr3+ in SrAl12O19 system. Two-step energy transfer is discussed, which involves two visible photons for each vacuum ultraviolet photon absorbed. [Copyright &y& Elsevier]

An approximately monochromatic red upconversion (UC) emission is successfully realized in NaScF 4 : Yb3+/Er3+ nanoparticles (NPs) through Mn2+ ions doping without phase transition. The Mn2+ ions play a role of bridge during the energy transfer process from green emission state 2H 11/2 /4S 3/2 of Er3+ to red emission state 4F 9/2 of Er3+, which significantly accelerates the red UC enhancement. The strongest red luminescence is observed in the sample containing 10% Mn2+ ions (Mn-10) with an enhancement factor of 7.5 times. Meanwhile, an ultrasensitive optical thermometry in the physiological temperature region can be realized by utilizing the fluorescence intensity ratio (FIR) between two thermally coupled Stark transitions of Er3+: 4I 13/2 → 4I 15/2 , locating in the near-infrared (NIR) long wavelength region of the second biological window. Its relative sensitivity S R can be expressed by 340/T2, which is much higher than most optical thermometers based on thermally coupled Stark sublevels reported by the previous papers. Beyond that, an ex vivo experiment is designed to evaluate the penetration depth of the red and NIR emission of Mn-10 in the biological tissues, revealing that they can reach depth of at least 3 mm and 5 mm respectively. More importantly, the increasing tissue thickness has almost no effect on the FIR values. All the results show that the present sample is a promising bi-functional nano probe which can be used for bioimaging and temperature sensing in the deep tissues through the strong red UC emission and ultrasensitive NIR optical thermometer, respectively. Deep-tissue bioimaging and optical thermometry can be simultaneously realized in Mn2+ doped NaScF 4 : Yb3+/Er3+ nanoparticles. Image 1 • Monochromatic red UC is realized in NaScF 4 : Yb3+/Er3+ NPs through Mn2+ ions doping. • Optical thermometry is realized by the long wavelength region of NIR-II window. • The penetration depth of 3 and 5 mm are reached by red and NIR light respectively. [ABSTRACT FROM AUTHOR]

Abstract: Ce3+ and Mn2+ co-doped Ca4Si2O7F2 phosphors have been synthesized by high temperature solid state reaction and their luminescence properties are investigated. The effect of Ce3+ concentration on the emission intensity of Ca4Si2O7F2: Ce3+ is studied, and the emission intensity reaches a maximum at 4% Ce3+. Energy transfer from Ce3+ to Mn2+ is observed. The emission spectra of the phosphors show a blue broad band at 460nm of Ce3+ and a yellow band at 580nm of Mn2+, originate from the allowed 5d→4f transition of the Ce3+ ion and the 4T1g(4G)→ 6A1g(6S) transition of the Mn2+ ion, respectively. Results indicate that the varied emitted color from blue to yellow can be achieved by tuning the relative ratio of the Ce3+ to Mn2+ ions based on the principle of energy transfer. We have demonstrated that Ca4Si2O7F2: Ce3+, Mn2+ phosphors can be a promising candidate for a color-tunable phosphor applied in a near-UV White light emitting diodes. [Copyright &y& Elsevier]

Abstract: Novel red long persistent phosphors of BaMg2Si2O7:Mn2+, Eu2+, Dy3+ have been synthesized at high temperature and weak reductive atmosphere. There are a deep blue emission with peak wavelength of 400nm and a broader emission band centered at 680nm when excited by 340nm. The broad emission band is attributed to the spin-forbidden transitions of the d-orbital electrons associated with the Mn2+ ions (4T1(4G)–6A1(6S)). The excitation and emission spectra of the samples with different dopants and doping concentrations show that the Mn2+ emission is dominantly due to the persistent energy transfer from Eu2+. Red long persistent phosphors have been observed in the system for over 2h. [Copyright &y& Elsevier]

Exploring new color-tunable phosphors is of significance for light-emitting applications. In this work, multicolor-emitting InNbTiO 6 :Dy3+,Eu3+ phosphors were formulated and synthesized using the classic solid-state reaction technique. Phase identification indicates the pure wolframite crystal structure of as-prepared samples. According to the Rietveld refinement, dopants have been confirmed to occupy the In3+ site in the InNbTiO 6 matrix. The phosphors exhibit strong absorption around 385 and 394 nm, due to the dominated transitions of 4F 9/2 ->6H 13/2 in Dy3+ and 5D 0 ->7F 2 in Eu3+, respectively, well matching the emissions from the commercial UV LED chips. In single doped phosphors, activators Dy3+ and Eu3+ under the UV light excitation respectively present their unique emission lines. As for the codoped phosphors, the co-activation and sensitization between Dy3+ and Eu3+ have been elucidated under a 394 nm excitation. The addition of Eu3+ into InNbTiO 6 :0.06Dy phosphor leads to the emission tuning from grass-green to orange-red crossing the warm-white region. The energy transfer can be proved through analyzing the PLE and PL profiles of the co-activated phosphors and evaluating the decay process for Dy3+ ions. According to the Dexter's theory and Reisfield's approximation, the mechanism of coupling effect has been identified to be the electric d-d (dipole-dipole) interaction. When the sum of dopants concentration equals to 0.09, the energy transfer efficiency reaches the maximum value 40.5. Moreover, the thermal stability of a representative InNbTiO 6 :0.06Dy3+,0.015Eu3+ phosphor have been investigated, which presented and a emission intensity maintenance of 42% at 423 K relative to room temperature 298 K. Besides, the quantum yields of InNbTiO 6 :0.06Dy3+, 0.04Eu3+ within the luminescence range 603–620 nm are measured to be 33.4% under the ultraviolet radiation of 394 nm. These results demonstrate that these new type phosphors have promising applications in UV LED based white light-emitting devices. Image 1 • The Dy3+-Eu3+ co-activated phosphors based on InNbTiO 6 have been prepared. • The dopants of Dy3+ and Eu3+ occupy the site of In3+ in the InNbTiO 6 host lattice. • The electric dipole-dipole interaction prompts energy transfer from Dy3+ to Eu3+. • The transfer efficiency from Dy3+ to Eu3+ reaches a high value 40.5. • These new type of phosphors demonstrate multicolor tunable property. [ABSTRACT FROM AUTHOR]