Eu[sup 2+]-Activated Ca[sub 8]Zn(SiO[sub 4])[sub 4]Cl[sub 2]: An Intense Green Emitting Phosphor for Blue Light Emitting Diodes

Abstract

We report intense green luminescence upon blue light excitation in Eu 2+ -activated Ca 8 Zn͑SiO 4 ͒ 4 Cl 2 prepared by high temperature solid state reaction with nominal composition of ͑2 − x͒CaO-xZnO-SiO 2 -CaCl 2 ͑0 ഛ x ഛ 1.1͒. It is observed that the material phase gradually converts from Ca 3 SiO 4 Cl 2 :Eu 2+ to Ca 8 Zn͑SiO 4 ͒ 4 Cl 2 :Eu 2+ followed by improved luminescent properties with increasing x. The two phosphors both emit with a maximum at 505 nm. Significantly, Ca 8 Zn͑SiO 4 ͒ 4 Cl 2 :Eu 2+ shows a more intense excitation band in the blue centered at 450 nm. Upon 450 nm excitation, the integrated emission intensity of Ca 8 Zn ͑SiO 4 ͒ 4 Cl 2 :Eu 2+ is 1.3 times stronger Ca 8 Mg͑SiO 4 ͒ 4 Cl 2 :Eu 2+ and nearly the same as Ca 3 Sc 2 Si 3 O 12 :Ce 3+ phosphors. Attempts to understand the origins of the intense luminescence are presented on the basis of diffuse reflection spectra and fluorescence decays of Ca 8 Zn͑SiO 4 ͒ 4 Cl 2 :Eu 2+ in comparison with related phosphors. The present results suggest that Ca 8 Zn͑SiO 4 ͒ 4 Cl 2 :Eu 2+ could be a promising green emitting phosphor for excitation by blue light emitting diodes.

Persistent luminescence in Ca8Zn(SiO4)4Cl2:Eu2+

“…Thermoluminescence glow curves were recorded on homemade TL Reader with a heating rate of 1.6 1C per second using RCA 931 B PMT which is sensitive over the region 380-650 nm with maximum sensitivity around 420 nm. [15]. The observed pattern matches very well with ICDD file no.…”

“…Ca 8 Zn(SiO 4 ) 4 Cl 2 was successfully prepared by the method described by Lu et al [15]. XRD patterns of the samples prepared matched very well with those reported by Lu et al Europium activated samples exhibit intense green persistent phosphorescence.…”

“…Polycrystalline Calcium Zinc Chlorosilicate was prepared by a solid-state reaction, following recipe given by Lu et al [15] using analytical reagent grade CaCO 3 , ZnO, SiO 2 and CaCl 2 . For doping, corresponding salts of the activators in the desired quantities were added.…”

Rondorfite-type structure—XPS and UV–vis study

“…However, the position of the photoelectron line of magnesium (Mg 2s) and silicon (Si 2p) as well as Al/Si and Al/Mg ratios for examined samples indicate another type of substitutions. What is more, tetrahedrally coordinated magnesium is far more susceptible to the isomorphic substitution [26,27]. It is also well reflected in the concentrations measured by XPS: the Al/Si ratio of 0.17/0.04 is smaller than Al/Mg ratio of 0.81/0.20 for the green and orange rondorfite, respectively.…”

“…Pb 2+ , Al 3+ , Cu 2+ , I 2+ [20][21][22][23][24][25]. Thus the synthetic analog of zinc rondorfite Ca 8 Zn(SiO 4 ) 4 Cl 2 [26,27] or magnesium rondorfite Ca 8 Mg(SiO 4 ) 4 Cl 2 [28][29][30] were considered by many authors as a matrix for doping to induce fluorescence effect. The strong luminescence emission in green light range has become a motivation for further investigation of the potential luminescent material (phosphor) for production of a new type of LEDs [8][9][10][11][12].…”