Literatura académica sobre el tema "5d-4f luminescence"

Luminescent properties of Sr9Lu(PO4)7 crystalline powders doped with Pr3+ ions upon excitation in the ultraviolet region of the spectrum are considered. in the temperature range 5-320 K, are considered.. In the photoluminescence spectra, an intense glow corresponding to radiative interconfigurational 5d->4f-electronic transitions, weak narrow lines of intra-configuration 4f->4f-transitions, and also the emission of two types of crystal structure defects, are observed, Under pulsed electronic excitation, the temporal characteristics of emission associated with an impurity center and defects and the temperature dependence of the luminescence yield were studied. The processes of energy transfer between defects and an impurity center are discussed. Keywords: 5d->4f luminescence, energy transfer, decay kinetics, ion Pr3+

Accurate and sensitive remote temperature measurement is required in a growing number of existing and emerging applications. As the technology advances and nanotechnology enters still new fields, the size of objects whose temperature needs to be controlled gets smaller and the non-contact temperature reading is the only reasonable approach. Luminescence thermometry is believed to become the technology of choice for such purposes, as it is resistant to disturbances by an electromagnetic field and the sensitivity and accuracy of measurements may be tuned for the specific requirements. Thus, whether it comes to reading temperature at cryo-range, around the room, or at high temperatures, one may design a luminescent thermometer offering high-quality measurements. This is not to say that such designing is easy to do. Even under laboratory conditions, highly-sensitive and accurate luminescent thermometers are not that frequent. Additional problems appear when it comes to measurements over a broad range of temperatures. At first, the basic physics of luminescence processes are not conducive to the design of a luminescence thermometer offering very sensitive and accurate measurements over a broad range of temperature (a few hundred degrees, for example). On the other hand, wide-range luminescence thermometers are of interest for such important fields as aviation and space industries. Fast, accurate, and credible measurements of quickly changing temperatures are of special importance in these areas. In this presentation, we shall report a new approach toward wide-range high-quality luminescence thermometry. Phosphors activated with either Pr3+ or Eu2+ will be examined for that purpose. Both these ions are capable of generating two types of emissions: (i) intra-configurational 5f→4f and inter-configurational 4f→4f ones. We shall prove that such phosphors may offer both broad-range and high-accuracy and high-sensitivity temperature measurements. Furthermore, we will demonstrate that the sensitivity of such sensors may be deliberately tuned to reach its maximum at temperatures where it is most needed. A few examples of such phosphors will be discussed and possible expectations for further development using this approach will be discussed. This research was supported by the Polish National Science Center (NCN) under the grant #UMO-2018/29/B/ST5/00420. Figure 1

The spectroscopic properties of several fluoride crystals ( LiYF 4, KYF 4, K 2 YF 5, KLiYF 5, CsY 2 F 7, SrF 2) doped with Nd 3+, Er 3+ or Tm 3+ are analyzed from the viewpoint of their possible applications as active media for VUV solid state lasers. It has been found that in many crystals there exists very efficient nonradiative relaxation from higher-lying 5d states to the lowest 5d level responsible for the spin-forbidden luminescence. In fact, the energy level diagram of 5d–4f transitions for these two ions represents a typical four-level laser scheme with a considerably larger Stokes shift of 5d–4f luminescence from the edge of the strong spin-allowed 4f–5d absorption than for Nd 3+, which causes smaller reabsorption of emitted VUV radiation in the crystals doped with Er 3+ or Tm 3+. Two crystals LiYF 4: Nd 3+ and SrF 2: Er 3+ were tested for laser action under pumping by a pulsed F 2 laser operating at 157 nm. However, no indications of the appearance of stimulated emission have been detected for both crystals. The possible reasons for the absence of lasing are discussed.

The results of the calculation of the energy band structure and luminescent research of CeF3 crystals are presented. The existence of two 5d1 and 5d2 subbands of the conduction band genetically derived from 5d states of Ce3+ ions with different effective electron masses of 4.9 me and 0.9 me, respectively, is revealed. The large electron effective mass in the 5d1 subband facilitates the localization of electronic excitations forming the 4f-5d cerium Frenkel self-trapped excitons responsible for the CeF3 luminescence. The structure of the excitation spectra of the exciton luminescence peaked at 290 nm, and the defect luminescence at 340 nm confirms the aforementioned calculated features of the conduction band of CeF3 crystals. The peculiarities of the excitation spectra of the luminescence of CaF2:Ce crystals dependent on the cerium concentration are considered with respect to the phase formation possibility of CeF3.

For optically active Ln3+ ions, fluoride is a very good luminescent substrate that has been used in the field of lasers, solid-phase optical transmitters, optical communications, up/down conversion. This work reports a systematic study on bridging between structure and tunable luminescence for SrF2:Ce3+/Ln3+ (Ln = Dy, Eu, Sm, Tb) nanoparticles. Regardless of the dopant level, all nanocrystals crystallized in a single cubic phase with the diameter of ∼20–30 nm. It was found that SrF2:Ce3+ exhibited intense ultraviolet emission under 288 nm excitation which can be attributed to the typical 4f-5d transition of Ce3+ ions. After the incorporation of Ln3+ ions, multicolor emission can be achieved when excited by the 4f-5d transition of Ce3+. This result gave an evidence that the excitation energy of Ce3+ canbe transferred toLn3+ leading to multicolor emission. The findings reported in this work may provide useful information in designing novel luminescent materials for tailored performances.

The mechanism of formation of emitting complexes is efficiently elucidated by in situ luminescence measurements of 5d–4f electronic transitions from the early stages of the reaction until the final product crystallization.

Efficient UV excitable Ce3+ ion activated SrWO4 phosphors, which were successfully prepared through a hydrothermal method. X-ray diffraction, field-emission scanning electron microscopy, CIE color coordinates and photoluminescence were used to characterize the samples. The effect of adding pH solution on the luminescent properties of SrWO4: Ce3+ was studied, the luminescence material SrWO4:Ce3+ exhibits intense blue photoluminescence (PL) with the maximum peak located at 306 nm, which is ascribed to the 4f→5d transition of Ce3+, All these results indicate that the SrWO4: Ce3+ phosphor holds tremendous potential for practical applications in and display with high performance LEDs.

Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(人間・環境学)<br>甲第21849号<br>人博第878号<br>新制||人||210(附属図書館)<br>2018||人博||878(吉田南総合図書館)<br>京都大学大学院人間・環境学研究科相関環境学専攻<br>(主査)教授 田部 勢津久, 教授 内本 喜晴, 教授 加藤 立久, 教授 吉田 寿雄<br>学位規則第4条第1項該当

Il lavoro presentato in questa tesi si pone l'obiettivo di studiare le proprietà ottiche e spettroscopiche di nuovi materiali luminescenti destinati ad applicazioni quali scintillatori veloci per moderne tecniche di diagnostica medica. Specificatamente la nostra attenzione è stata rivolta alla sintesi di materiali inorganici ad ampio band-gap attivati con lo ione trivalente praseodimio (Pr3+) il quale, in seguito ad opportuna eccitazione, può dare luogo ad emissioni radiative veloci (15-25 ns) potenzialmente utili nella realizzazione di scintillatori. Le prestazioni dei scintillatori sono determinate prevalentemente dalla dissipazione dell'energia assorbita in seguito all' irradiazione del materiale attraverso una sequenza di processi che portano infine all'emissione di radiazione visibile o ultravioletta. Lo studio e la comprensione dei meccanismi di rilassamento, migrazione e trasferimento dell'energia assorbita dal materiale ai difetti e/o impurezze è fondamentale per la progettazione di nuovi materiali ottici dalle prestazioni avanzate, soprattutto in termini di efficienza quantica, velocità di risposta, stabilità termica e chimica. Nel presente lavoro di tesi sono stati preparati e caratterizzati campioni di Ca9LuPO4:Ce3+/Pr3+, K3Lu(PO4)2:Pr3+, KLuP2O7:Pr3+, X2SiO5:Pr3+ (X= Y, Lu) come polveri policristalline e BaMgF4:Nd3+ come cristallo singolo. Per ciascun materiale è stato quindi condotto uno studio ottico sistematico mediante spettroscopia di luminescenza risolta nel tempo e dinamica di stato eccitato al fine di comprendere la struttura elettronica dei centri luminescenti, l'influenza dei difetti reticolari e i principali meccanismi responsabili dei trasferimenti energetici tra matrice e ione luminescente. L'attività di ricerca proposta in questo progetto di tesi porrà le basi per lo sviluppo di adeguati modelli sulle modalità di trasferimento energetico in nuovi materiali scintillatori attivati con ioni lantanidi, portando infine alla possibilità di progettare materiali dalle proprietà ottiche opportunamente selezionate e all'ottimizzazione delle prestazioni di materiali già in uso.<br>The work presented in this thesis is focused on the development and improvement of new wide band-gap luminescent materials used as fast scintillators in modern medical diagnostic techniques. The goal of this research consists in obtaining inorganic scintillators activated with trivalent preaseodymium (Pr3+) ion where a very fast interconfigurational d-f emission could be observed. The performance of scintillator materials is determined by the dissipation of high energy photons in a sequence of processes ultimately leading to the emission of visible or UV radiation. The understanding of the processes responsible for relaxation and migration of electronic excitations, and the transfer of energy to defects and impurity centers is crucial for successful development of new optical materials with enhanced performance, especially in terms of quantum efficiency, temporal response, radiation resistance, thermal and chemical stability. In the present work polycrystalline powders of Ca9LuPO4:Ce3+/Pr3+, K3Lu(PO4)2:Pr3+, KLuP2O7:Pr3+, X2SiO5:Pr3+ (X= Y, Lu) and single crystals of BaMgF4:Nd3+ were synthesized and characterized. A systematic study of time-resolved luminescence spectra and luminescence decay profiles of these materials was performed at the HASYLAB, DESY synchrotron facility in Hamburg (Germany) in order to understand the electronic structure of luminescent centers, the influence of defects, and the main mechanisms responsible for host-to-impurity energy transfer and relaxation of the host electronic excitation. The research proposed in this project will allow developing an adequate model of creation and relaxation of electronic excitations establishing the main principles for the synthesis of new materials with controllable optical and luminescence properties.