A new kind of glass-ceramic phosphor, which contains crystalline phases with green emissions, is explored. The glassceramic is prepared through semi-melt-quenching procedure with a nominal composition of （Ca0.99Eu0.01）3Si2O7. The greenemitting crystals are precipitated and identified to be β-Ca2SiO4： Eu2＋ which is responsible for 510 nm-peaked much broader band emissions holding at 1550 ℃ for half an hour. In terms of the available light scattering theory, the appearance of opaque is discussed by closely associating with size and morphology of luminous β-Ca2SiO4 crystalline phase in glass.
A distinct red-shift to 660 nm-featured longer wavelength of europium doped calcium sulphide nanocrystals was observed in a microwave （MW）-assisted solvothermal synthesis procedure. This red-shift was probably due to a combined effect from Mg^2＋ codoping and strain accumulation at grain boundaries. The latter originated from the formation of small grains with an average size of around 200 nm in micrometer sized crystals upon Mg^2＋ codoping. In particular, MW electromagnetic field suppressed grain growth and enabled a reconstruction of atoms at the inner grain boundary at which the field strength was intensified around rare earth ions in host lattices. This MW synthesis route provided an option to prepare luminescent crystals with the desired blue-excitable longer wavelength emission.
Eu2+ -activated reddish-orange-emitting Ca3Si2O7 phosphors were synthesized with the addition of NH4Cl flux.When the phosphors were synthesized in a nominal composition of (Ca0.99Eu0.01)3Si2O7 without flux addition,a Ca3Si2O7 phase responsible for reddish-orange emission was identified to coexist with an intermediate phase of a-Ca2SiO4 for green emission.With the addition of NH4Cl flux,a-Ca2SiO4 was suppressed while the pure phase Ca3Si2O7 was obtained as the flux content was 3 wt%.Through varying the amount of flux,the emission color of samples can be tuned from green to reddish-orange,corresponding to the phase transformation from a-Ca2SiO4 to Ca3Si2O7.Through optimizing the doping concentration of Eu2+ ,the optimized photoluminescence (PL) properties for reddish-orange emission can be achieved,which makes this kind of phosphor prospective in the applications of the phosphor-converted white light emitting diodes (PC-WLEDs).
A solid-solution-phase Ba1.75Ca1.25MgSi2O8： Eu2＋, Mn2＋ phosphor in the photosynthetic action spectrum with dual band emissions at 438 nm and 660 nm is fabricated. X-ray diffraction （XRD） confirms the presence of the solid-solution phase. With the supporting information from the diffuse reflection spectrum, a feasible way to obtain higher energy-transfer （ET） efficiency is attained, and the ET efficiency of Eu2＋-Mn2＋ is enhanced to 76%. The mechanism of this enhancement is owing to variation of the solid solution composition of Ca3MgSi208 and Ba3MgSi2Os, which contributes to the extension of the critical distance. Temperature-dependent results show an en- hancement which is attributed to Ca. These enhancements show great promise for improving coo-lighting devices.
Aprototype of YAG： Ce （Y3Al5O12） luminous bulk ceramic as a remote phosphor for white LED illumination was fabricated in air through a strategy of silica addition. With increasing the amount of silica in a specific range, the opaque sample turns to be semi-transparent. The precipitation of crystals is verified to be in pure YAG phase by X-ray diffraction （XRD）. Beyond the limit of silica amount, the dominant phase of YAG crystal is found to coexist with a small amount of newly-formed Y2Si2O7, Al2O3 and the amorphous phase. The YAG crystals are with a grain size of approximately 2 μm and distribute evenly. The YAG hosts after structural modification via addition of silica result in yellow band emission of 5d → 4f transition peaked around 535 nm as excited by a blue LED, owing to the self-reduction of Ce^4＋ to Ce^3＋ even in the absence ofreductive atmosphere.
Morphology control of cage-like （Ba,Sr）3MgSi2O8：Eu,Mn luminous sphere in micrometer size with a simultaneous 660 nm/430 nm-featured band emission was investigated via microwave （MW） firing procedure. A firing temperature range associated with distinct reaction of xerogel particles was determined by thermal analysis, at which the pure host phase of （Ba,Sr）3MgSi2O8 was formed and the release of decomposed gas from the precipitated nitrates played a key role in controlling the multi-scale structured morphology. As-prepared Ba1.14Sr1.7MgSi2O8：0.06Eu2＋,0.1Mn2＋ samples featured in a band emission simultaneously emitting at both 660 and 430 nm under 350 nm light excitation by MW procedure with an enhancement emission compared to the sample by solid state procedure. The results suggested that MW firing procedure affected assembling cage-like particle in meso-, nano- and submicro- meters to achieve photoluminescence （PL） enhancement of the simultaneous red/blue emission.
