Intense Luminescence From Higher Level Of Eu³⁺ In Cala-apatite Silicate: Eu^（2+,3+） And Its Origin

The phosphor of CaLa-oxyapatite:Eu(2+,3+)was synthesized vianormal solid-state reaction method in weak reduction atmosphere. TheXPS spectrum of Eu4d level can be fitted to four photoelectric peaks, theratio of Eu3+and Eu2+is2:1. The intense emission lines from transitions5D71-F7Jand weak lines from5D2-FJof Eu3+are present in the emissionspectra besides lines from5D70-FJunder the excitation of the chargetransfer state (CTS) of Eu3+ion or Eu2+. The transitions of excitation andemission spectra were identified. The emission of high levels originatesfrom the luminescence center Eu3+at4f site and Eu2+occupy4f site for itradius. The decay curves of emission lines from levels5D50,5D1, andD2under excitations of CTS, Eu2+and level5D2could be fitted intobi-exponential decays. The lifetimes of5D1emission are much longerthan that of5D0emission. The analysis of lifetimes shows that excitationinto CTS following a energy transmission to5D1would be in theassistance of Eu2+and the energy transmission from5D51toD0isinterfered. As a result, the intense luminescence of5D1level is achieveddue to the enhanced probability of radiation transition. Three series ofsharp peaks brought about by absorption of oxygen vacancies in theexcitation spectra of monitored at different wavelengths. There are twopossible routes to transmit the excitation energy, one is directly to levelsof Eu3+and another is that the oxygen vacancies trap the energy and thenreleased it again. The second way result in the ultra long lifetime andsuper intensity of5D1emissions.The phosphor has three kinds of luminescence centers and theirsituations in crystallographic sites were surmised based on selectiveexcitation spectrum. Various concentrations of Eu were doped into thehost of CaLa-oxyapatite, the relative intensity of5D1emission lines ischanged with concentrations of Eu doped. The line of622.5nm haveabnormal lifetime under excitations of Eu2+. The phosphor ofCaLa-oxyapatite:Eu(2+,3+)was prepared by different method, and thephosphor synthesized via solid-state reaction method good performancein luminescence. Series phosphors were prepared via same amount of Pand B substitution of Si in the acid radical. The a, c, V decrease and thepeak positions of CTS and Eu2+are red shift with the B, P increases.Large amont of B, P substitution is beneficial to622.5nm line.