Temperaturska zavisnost luminescencije neorganskih fosfora na bazi retkih zemalja

Abstract

Fosfori na bazi retkih zemalja predstavljaju važnu grupu materijala koja nalazi primenu u medicinskoj tomografiji, fizici visoke energije, proizvodnji scintilatora, lampi i displeja [1] . Upotreba ovih materijala kao temperaturskih senzora u poslednje vreme postala je veoma interesantna [2] [3]. Predmet istraživanja ovog rada bio je temperatursko gašenje luminescencije fosfora na bazi retkih zemalja. Analizirane su matrice ortovanadata i seskvioksida dopirane jonima europijuma (Eu3+), disprozijuma (Dy3+) i samarijuma (Sm3+). Pokazana je temperaturska zavisnost luminescentnih emisionih spektara ovih materijala, koja nalazi praktičnu primenu u merenju temperature. Kako rezultati dobijeni merenjem emisionih spektara u funkciji temperature nisu pogodni za opisivanje fenomena temperaturskog gašenja luminescencije, izvršena su merenja vremena života pobuđenog stanja dopantnih jona. Pokazano je da postojeći modeli, model multifononske relaksacije i model neradijativnog pražnjenja preko CT nivoa (nivoi sa prenosom naelektrisanja, engl. Charge transfer states) ne daju zadovoljavajuće rezultate. Analizom ekscitacionih spektara pokazano je da CT nivo nema fiksnu vrednost već da se njegova energija menja sa promenom temperature. Na osnovu datih merenih rezultata izvršeno je unapređenje postojećeg modela neradijativnog pražnjenja preko CT nivoa koji uključuje temperatursku zavisnost energije CT stanja. Poređenje postojećih modela i modela temperaturski zavisnog CT stanja pokazano je bolje slaganje ovog modela sa eksperimentalnim rezultatima.

The rare earth based inorganic phosphors are a significant group of materials which are commonly used in medical tomography, high energy physics, the production of scintillators, lamps and displays. [1] Using these materials as temperature sensors has lately become a very interesting topic. [2] [3] The topic of this research is temperature quenching of luminescence of rare earth doped phosphors. The matrix of orthovanadates and sesquioxides doped with Europium (Eu3+), Dysprosium (Dy3+) i Samarium (Sm3+) ions has been analyzed. We have shown the temperature dependence of luminescent emission spectra of these materials and their practical use in the temperature measurement. Lifetime measurements are performed for the excited states of the rare earth ions due to the fact that the results obtained from testing the emission spectra as a function of temperature were not suitable to describe the temperature quenching of luminescence. This thesis showed that the existing models, multiphonon relaxation and temperature quenching through CT (charge transfer) state, do not provide the satisfactory results. By analyzing the excitation spectra we have shown that the CT level does not have a fixed value but its energy changes with the temperature change. Based on the experimental results, an improvement of the existing model (temperature quenching through the CT state) has been given, taking into account the temperature dependence of the CT state. The comparison of the temperature dependent CT state model to the existing models has shown its better correspondence to the obtained results.