The exploration of stable/efficient phosphor for n-UV chip pumped white light-emitting diodes (wLEDs) remains an arduous task. Herein, a novel series of color tunable Eu2+/Tb3+/Sm3+ tridoped Sc-based cyclosilicate phosphors (KBaScSi3O9: Eu2+/Tb3+/Sm3+) have successfully designed and obtained via facile solid-state reaction based on comprehensive consideration of rigidly structural network of host, weak electron-phonon coupling strength and spectral adjustability of codopants via energy transfer (ET). The crystallographic occupancies of Eu, Tb and Sm primary in Ba/K, Ba and Ba sites in the monoclinic host, respectively were determined on the basis of the Rietveld refinements and crystal chemistry rules. The photoluminescence (PL) properties were systematically investigated in conjunction with structural analyses, implying that the 'warm' white light with excellent thermal stability is stemmed from combination of optimized blue (Eu2+), green (Tb3+) and red (Sm3+) emissions via Eu -> Tb -> Sm ET strategy. Interestingly, Tb ions play both roles of green light luminescent center and ET bridge to achieve cascade ET for connecting Eu/Sm ion pairs because of the adverse metal-metal charge transfer (MMCT) effect (Eu2+ + Sm3+ -> Eu3+ + Sm2+). Furthermore, the phosphor-converted wLEDs (pc-wLEDs), by encapsulating the optimal KBS: 4 %Eu/4 %Tb/6 %Sm with commercial n-UV LED chip, show high thermal stability with satisfactory electroluminescence (EL) performances. These results indicate the KBS: Eu/Tb/Sm phosphors are potential candidates for application in high power n-UV pumped pc-wLEDs.

The phosphor-converted white light-emitting diodes (pc- w LEDs) are current research hotspot. To meet simultaneously the requirements of high chemical/thermal stability and color-rendering index (CRI), low correlated color temperature (CCT) for actual application is still not be perfectly achieved. Herein, we studied for the first time the incorporation of Ce 3 + (blue-emitting) and Mn 2 + (orange/red emission) into the dibarium magnesium phosphate ceramic (Ba 2 Mg(PO 4 ) 2 , BMP) for packaging of pc- w LEDs via remote 'capping' approach, which exhibits highly efficient color-tunable photoluminescence (PL) with splendid chemical/thermal stability, singlephase/full-color-PL, efficient energy transfer (ET). To reduce the impact of heterovalent substitution (Ba 2 + <- Ce 3 + ), the monovalent (Li + , Na + , K + ) ion, respectively tridoped in BMP: Ce/Mn and played both roles as flux and charge compensator, were also studied/compared on the basis of PL efficiency, where Na + is the most effective because of the lowest electronegativity mismatch between the Ba 2 + and Na + . An alkaline-earth-metal-ion blending strategy via partial replacement of Ba 2 + with Sr 2 + was implemented to further regulate PL and obtain better parameters of CCT/CRI due to the variations of crystal field splitting. The site occupations of Ce/ Na/Sr in Ba sites ( CN = 8 and 7) and Mn in Mg site ( CN = 6) were based on the comparisons of ion radius and confirmed by XRD/Rietveld analyses, where Ce/Na/Sr ions gave priority to occupy the Ba site with CN = 8 due to their much closer ion radius. Altogether, the stably composition-optimized BMP: Ce/Mn/Na/Sr has great potential application as a single-component color-tunable phosphor in n -UV pumped pc- w LEDs.

Rare-earth (RE) and/or transition metal (TM) ions (co)doped phosphors have garnered much attention for promoting development in the fields of solid state lighting (SSL) and displays. It is a meaningful work to design high-quality phosphor via intelligent assembling from wide variety of compounds with RE/TM ions. Herein, the lanthanum borophosphate La7O6(BO3)(PO4)2 (LOBP) and Bi/Eu were selected as host and dopants for constructing the phosphor LOBP: Bi/Eu via solid phase synthetic method due to simple synthesis, chemical/thermal stability, rich cationic sites, appropriate bandgap, and controllable optical tuning from synergistic effect of cyan (Bi) and red (Eu) emissions, respectively. The structure and site occupations were analysed via XRD and Rietveld refinements, showing Bi3+ ions were only resided in La3+ sites within the monoclinic matrix (P21/n) and appeared greater inclination towards the La sites with coordinate number (CN) = 8 as compared with CN = 7 due to the closer ion radius ratio. While Eu3+ ions entered into the two distinct La sites with almost the same probability. The morphology and elemental mapping were obtained via SEM/EDS, exhibiting irregular particle shape with micron-level size, and the chemical composition met expectation. Through energy transfer (ET) from Bi to Eu under n-UV excitation, the adjustable photoluminescence (PL) from cyan traversing white and finally to red could be achieved. The concentration quenching for both singly- (Bi) and co-doped (Bi/Eu) phosphors were charged by the d-d interactions. Finally, the stable as-fabricated n-UV pumped wLED via coupling the composition-optimized white-emitting LOBP: 2%Bi, 7%Eu to a commercial 305 nm n-UV LED chip shows splendid performances.

Phosphor-converted white light-emitting diodes (pc-wLEDs) have attracted attention in the field of solid-state lighting. Selection and study of suitable single-phase phosphor and packaging modes are currently the main research hotspots. Herein, color-tunable photoluminescence (PL) and thermally stable tri-doped Melitite Sr2MgSi2O7:Ce/Tb/Sm are systematically studied via structural and static/dynamic spectral analyses. All dopants could only be accommodated in the Sr site due to similar ionic radii. Previous studies have concluded that green and red PL could be obtained from singly doped Tb and Sm phosphors with excellent reproduction, and color tunable PL can be achieved from Ce/Tb co-doped phosphors. The forbidden 4f-4f transitions of Tb/Sm cause low efficiency and Ce/Tb co-doping cannot achieve white light emissions. Alternatively, co-doping allowed 5d-4f transition sensitizer with emissions in the UV-blue region (i.e., Ce), color-tunable PL (including the white light); high efficiency of Sr2MgSi2O7:Ce/Tb/Sm could be achieved via energy transfer (ET) from Ce -> Tb -> Sm. The impossibly direct ET from Ce -> Sm is associated with the side metal-metal charge transfer (MMCT) effect. Due to chemically nonequivalent substitutions, two positive Ce(Tb,Sm)(Sr) and one negative V" (Sr) were created to maintain the whole charge balance. To reduce the defects and allow more dopants to enter into the Sr site, Na+ was added as a charge balancer to enhance PL efficiency. Furthermore, an alkaline-earth-metal-ions blending strategy via partial replacement of Sr with Ba was investigated to regulate PL owing to the change in crystal field splitting. PL blue-shifted by Ba-co-doping, which could increase the degree of overlapping and enhance ET efficiency. As a proof-of-concept experiment, the pc-wLED fabricated via a combination of the optimal Sr(Ba)(2)MgSi2O7:Ce/Tb/Sm/Na and an n-UV LED chip based on a remote 'capping' packaging mode shows excellent performances, indicating its strong potential application in the field of solid-state lighting.

Phosphor-converted white light-emitting diodes (pc-LEDs) have attracted attention in the field of solid-state lighting. Selection and study of suitable single-phase phosphor and packaging modes are currently the main research hotspots. Herein, color-tunable photoluminescence (PL) and thermally stable tri-doped Melitite SrMgSiO:Ce/Tb/Sm are systematically studied structural and static/dynamic spectral analyses. All dopants could only be accommodated in the Sr site due to similar ionic radii. Previous studies have concluded that green and red PL could be obtained from singly doped Tb and Sm phosphors with excellent reproduction, and color tunable PL can be achieved from Ce/Tb co-doped phosphors. The forbidden 4f-4f transitions of Tb/Sm cause low efficiency and Ce/Tb co-doping cannot achieve white light emissions. Alternatively, co-doping allowed 5d-4f transition sensitizer with emissions in the UV-blue region (, Ce), color-tunable PL (including the white light); high efficiency of SrMgSiO:Ce/Tb/Sm could be achieved energy transfer (ET) from Ce → Tb → Sm. The impossibly direct ET from Ce → Sm is associated with the side metal-metal charge transfer (MMCT) effect. Due to chemically nonequivalent substitutions, two positive Ce(Tb,Sm) and one negative V'' were created to maintain the whole charge balance. To reduce the defects and allow more dopants to enter into the Sr site, Na was added as a charge balancer to enhance PL efficiency. Furthermore, an alkaline-earth-metal-ions blending strategy partial replacement of Sr with Ba was investigated to regulate PL owing to the change in crystal field splitting. PL blue-shifted by Ba-co-doping, which could increase the degree of overlapping and enhance ET efficiency. As a proof-of-concept experiment, the pc-LED fabricated a combination of the optimal Sr(Ba)MgSiO:Ce/Tb/Sm/Na and an -UV LED chip based on a remote 'capping' packaging mode shows excellent performances, indicating its strong potential application in the field of solid-state lighting.

For n-type PbTe based compounds with relatively low optimal concentration (10(19) cm(-3)), the accompanied structural defects play pivotal role on the charge transport upon doping with alien valent atoms. Herein, we report that Oxygen has huge influence on the defect evolution and thermoelectric properties in n-type PbTe for the first time. A boosted thermoelectric figure of merit ZT of similar to 1.12 at 673 K and a ZT(ave) of 0.84 in the range of 300-873 K are achieved for vacuum sintered Bi-doped PbTe with the powders ground under the protection of Ar. This is in sharp contrast with the same Bi-doped PbTe material sintered with the powders ground in the air, which reaches a ZT(ave) of 0.52. This distinct thermoelectric properties in Bi-doped PbTe compounds are strongly correlated to Bi dopant, the vacancy defects (V-Pb '' and V-Te(center dot center dot)) induced during the fracturing process, and oxygen in the air. The coexistence of Bi dopant and oxygen lowers the formation energy of Pb vacancies and induces large number of O-Bi related Pb vacancies in the structure, yielding an acceptor-like effect. Such negatively charged Pb vacancies in the structure exert a strong long-range coulombic repulsion force on the electrons, leading to a low doping efficiency, a low carrier mobility (200 cm(2) V-1 s(-1)), and inferior electronic properties. Whereas, the protection provided by Ar effectively avoids the contamination by oxygen and prevents the formation of O-Bi related Pb vacancies, which appears remarkably effective in enhancing the electronic transport. A high carrier mobility of 1300 cm(2) V-1 s(-1) is attained in slightly doped Pb0.9995Bi0.0005Te sample and this contributes to an ultra-high power factor of 40 mu W cm(-1) K-2 for the Pb0.9995Bi0.0005Te sample at room temperature. The high PFave exceeds 25 mu W cm(-1) K-2 in the range of 300-723 K. The work provides a new insight into the formation mechanism of structural defects and a new avenue for suppressing the cation vacancies, resulting in higher performance of n-type PbTe-based compounds.