Improved photo-luminescence behaviour of Eu³⁺ activated CaMoO₄ nanoparticles via Zn²⁺ incorporation

Abstract

Zn 2+ (0, 2, 5, 7 and 10 at.%) co-doped CaMoO 4 :2Eu 3+ nanophosphors have been synthesized via polyol method using ethylene glycol (EG) as both capping agent and reaction medium at 150 o C.From XRD analysis, all 900 C annealed, Zn-co-doped CaMoO 4 :Eu 3+ have tetragonal scheelite phase.Some extra phase evolution has been observed for ASP Zn doped samples. Intensity and crystallinity of XRD patterns increase as heat treatment increases to 900 C. Valence state of the involved compositions (Zn co-doped CaMoO 4 : Eu) was investigated by X-ray photoelectron spectroscopy (XPS) and found that Ca, Mo, Eu and Zn are in their +2, +6, +3 and +2 oxidation states, respectively. TG-DSC studies of the as-prepared samples corroborate their thermal stability. TEM study reveals that particles have spherical morphology. Photoluminescence studies have been studied under ~266, and 395 nm excitation wavelengths. Zn co-doping in CaMoO 4 :Eu matrix, produces the high distortion and modify the crystal field around Eu 3+ ion and improves the PL intensity. CIE co-ordinates of 900 o C annealed 10 at.% Zn codoped CaMoO 4 :Eu sample under 266 nm excitation is x = 0.64 and y = 0.35, which are closer to the standard of NTSC (x = 0.67 and y = 0.33). CCT values vary for ASP and annealed samples at different excitation wavelengths. These investigations reveal that Zn co-doped CaMoO 4 :Eu 3+ nanophosphors can be used as potential red emitting phosphor which is bottleneck in the advancement of LEDs at much lower cost.performed to improve the luminescent properties of CaMoO 4 phosphor by co-doping of other metal ions. However, low efficacy of these nano-materials confined their generalised applications. Consequently, it will be of great interest to significantly enhance the emission intensity of phosphors in order to deploy their potential applications.The energy transfer mechanism from a sensitizer to an activator such as Eu 2+ /Mn 2+ , Ce 3+ /Mn 2+ , and Ce 3+/ Eu 2+ couples has been investigated in many inorganic hosts, and an effective resonancetype multi polar interaction has been verified in NaSr 4 (BO 3 ) 3 : Ce 3+ /, Mn 2+ , NaBa 4 (BO 3 ) 3 : Ce 3+ /Mn 2+ , Sr 3 Sc(PO 4 ) 3 : Eu 2+ / Mn 2+ ,Sr 3 B 2 O 6 : Ce 3+ , Eu 2+ ,and so on. Moreover, some single-phase phosphors, such as Ca 10 K(PO 4 ) 7 :Eu 2+ / Mn 2+ , Ca 9 Y(PO 4 ) 7 : Eu 2+ /Mn 2+ , Ca 9 Y(PO 4 ) 7 : Ce 3+ / Eu 2+ ,and Ca 9 Y(PO 4 ) 7 : Ce 3+ /Mn 2+ , are used to improve the emission intensity for n-UV LED (light emitting diode) applications. 11,13,14 Also an improvement in photo-luminescence intensity has been reported with co-doping of charge compensators such as Li + , K + , Na + and Bi 3+ in phosphors or with SiO 2 coating over particle of phosphor. In this direction, non-radiative rates are reduced by either charge compensation, improve crystallinity or extent of decrease of surface dangling bonds/OH bonds by shell from inner core phosphor. 15 Su and their co-workers also reported the enhanced photoluminescence in CaWO 4 based red phosphor via Eu and Na co-doping. 16 There ...

Enhanced Pr3+ photoluminescence by energy transfer in SrF2 : Eu2+, Pr3+ phosphor

“…SrF 2 stands out as an excellent host for various lanthanide ions due to its wide transparency window in visible spectrum and further reduced multiphonon relaxation rates as compared to other hosts such as YPO 4 and CaMoO 4 . [15][16][17] The YPO 4 and CaMoO 4 hosts have relatively high multiphonon relaxation but they can be prepared at a very low temperature. 17,18 In SrF 2 crystals, lanthanide ions form clusters in SrF 2 as a result of the need for charge compensation when divalent Sr 2+ is substituted by trivalent Pr 3+ .…”

Influence of doping alkali metal ions on the structure and luminescent properties of microwave synthesized CaMoO4:Dy3+ phosphors

“…They are able to emit characteristic transitions of 4 F 9/2 → 6 H 15/2 (blue) and 4 F 9/2 → 6 H 13/2 (yellow). The blue 4 F 9/2 → 6 H 15/2 transition is magnetic dipole transition, which is not easily affected by the surrounding environment, while yellow 4 F 9/2 → 6 H 13/2 transition is a highly sensitive electric dipole transition influenced by the microscopic environment [8].…”

“…As one of the members of metal molybdates, CaMoO 4 has the C 4h 6 symmetry and I4 1 /a space group. In the lattice, each Mo atom is surrounded by four oxygen atoms forming [MoO 4 ] polyhedral while each Ca atom is besieged by eight oxygen atoms building [CaO 8 ] polyhedral [4]. Due to their unique structure, good thermal and chemical stability and perfect luminescence properties, CaMoO 4 is a favorable host and has been widely utilized in scintillators, solid state lasers, fluorescent lamps and catalysts, etc.…”

“…Upon host excitation at 301 nm, the photon energy is absorbed by the host and efficiently transferred from MoO4 2-to Dy 3+ .…”

Growth and optical properties of ZnWO4 single crystals pure and doped with Ca and Eu

“…all [8] have observed a significant energy transfer from WO42-groups to Eu3+ ions. Singh et al [9] has codoped CaMoO4:Eu3+ nanophosphors with Zn2+ and have found that Zn co-doping (up to 10 at.%) in CaMoO4:Eu3+ matrix produces the high distortion and asymmetry and can modify the crystal field around Eu3+ ion as well as improve the PL intensity. Enhanced photoluminescence of 900 o C annealed samples has been found comparable with the one obtained for samples prepared by Zn-doping.…”