Luminescence and scintillation characteristics of four selected material systems, namely CsI:Tl(Na), CeF 3 , PbWO 4 and Ce-doped aluminium perovskites XAIO 3 :Ce (X=Y, Lu, Y-Lu) are reviewed. The progress in their physical understanding and related optimisation of their characteristics and technology are demonstrated. The important role of various defect states in the scintillator performance of these materials is stressed, which has led to the need for a deeper study of the processes of energy transfer and storage to achieve their intrinsic limits and full exploitation in scintillation detectors.

Wide Band Gap Scintillation Materials: Progress in the Technology and Material Understanding

We have fabricated Cr 3+ and Nd 3+ co-doped YAG (Cr;Nd:YAG) ceramics, and investigated their optical properties and laser characteristics. The Cr;Nd:YAG has two broad absorption bands at around 440 nm ( 4 A 2 → 4 T 1 ) and 600 nm ( 4 A 2 → 4 T 2 ) respectively, caused by Cr 3+ ions. In the case of pumping at 440 nm, the maximum effective lifetime of the Cr;Nd:YAG was 737 μs with a 0.1 at% Cr 3+ and 1.0 at% Nd 3+ co-doped YAG sample. Cr 3+ ions take a role of an effective sensitizer to convert the UV light of flashlamp. For single-shot laser operation, a 10.4 J output energy at 1064 nm was obtained with 0.1 at% Cr 3+ and 1.0 at% Nd 3+ co-doped YAG ceramic rod with a laser efficiency of 4.9%. The laser efficiency was found to be more than twice that of a 1.0 at % Nd 3+ :YAG ceramic rod.

The optical properties and laser characteristics of Cr3+ and Nd3+ co-doped Y3Al5O12 ceramics

In YAlO3 crystals grown in vacuum or reduced by annealing at low oxygen pressure, the luminescence of F centers in the band at 420 nm, with τ=30 ms at 9 K, excited in the bands at 212 and 242 nm, as well as the luminescence of F+ centers in the band at 355 nm, with τ=2.7 ns, excited in the main band at 220 nm and weaker bands at 190 and 288 nm, was detected. On the basis of the results obtained and data in the literature, the behavior of the emission of F+ and F centers in oxides of the Al2O3-Y2O3 system is analyzed on the example of the compounds α-Al2O3, YAlO3, and Y3Al5O12. The role of antisite defects in the stabilization of F-like luminescence and absorption centers in multisublattice oxides is discussed.

Luminescence of F+ and F centers in YAlO3

A flashlamp-pumped highly efficient 0.1 at. % Cr3+ and 1.0 at. % Nd3+ codoped Y3Al5O12 ceramic laser was demonstrated. A 10.4 J output energy at 1064 nm was obtained, with a laser efficiency of 4.9%. The laser efficiency of the Cr3+ and Nd3+ codoped Y3Al5O12 ceramic rod was found to be more than twofold that of a 1.0 at. % Nd3+-doped Y3Al5O12 ceramic rod.

https://iopscience.iop.org/article/10.1143/JJAP.45.133/pdf

Highly Efficient Flashlamp-Pumped Cr3+ and Nd3+ Codoped Y3Al5O12 Ceramic Laser

The polarization diagrams of the luminescence at 400 nm of colour centres in YAG crystals have been measured under excitation in absorption bands at 370 and 235 nm. The results suggest that the centre is most likely to be a one-electron centre involving an oxygen vacancy and a perturbing agent in the adjacent Al(Oh) site.

https://iopscience.iop.org/article/10.1088/0953-8984/3/28/021/pdf

Polarization of luminescence of colour centres in YAG crystals

Nonstoichiometric defects in YAG and YAP

The colour changes of YAG crystals doped with Ti, V, Cr, Mn, Fe, Co and Ni as well as those doped with Mg or Be are described The comparison of samples annealed in hydrogen oxygen and argon and exposed to an UV irradiation is given Yellow or brown colour of YAG crystals is attributed to the O− centre formation which causes an increase of absorption, particularly near 400 nm Most intensive coloration showed the crystals containing iron group ions in a higher valency state after UV irradiation and some crystals (e g YAG:Cr) annealed in argon



Es wird die Farbanderung von YAG-Kristallen, die mit Ti, V, Cr, Mn, Fe, Co, Ni oder mit Mg und Be dotiert wurden, beschrieben Proben, die in Wasserstoff, Sauerstoff und Argon getempert und einer UV-Bestrahlung ausgesetzt wurden, werden verglichen Gelbe oder braune Farbe von YAG-Kristallen wird der O−-Zentrenbildung zugeschrieben, die ein Anwachsen der Absorption, vor allem zwischen 380 und 420 nm hervorruft Kristalle mit mehrwertigen Ionen weisen nach der UV-Bestrahlung und einige Kristalle (z B YAG:Cr) nach der Temperung in Argon deutliche Absorption aus

O− centre formation in YAG crystals doped with iron group ions

Transient absorption of a long lifetime (≧ 20 s) of YAG: Nd is typical of pure material. It is the main reason of thermal deformation of the laser rods accompanied with power decreases at higher CW input. It may be prevented by an admixture of Fe, Ti or Cr. Using a small admixture (≦ 10−3 wt.%) of Ti or Cr the energy transfer among Nd ions and the gain coefficient may be increased. Cr in a higher concentration absorbs the pumping light and serves as earlier described coactivator (sensitizer) only. Fe impurity fully prevents any increase of the gain of YAG: Nd containing Ti or Cr and causes slow but irreversible degradation of the active parameters. Ce favourably modifies properties of YAG: Nd, Cr. YAG: Nd, Cr, Ce free of iron impurity is advisable active material for powerfull CW lasers.

Laser properties of yag: Nd, Cr, Ce

Thermoluminescence (TL) of several types of corundum crystals is described. Undoped crystals showed a weak TL at 15 and 110°C with emission at 330 and 495 nm. Good TL response at 275°C is shown by Cr doped (0.03 wt%) crystals grown by Verneuil method in the oxygen cone of the flame annealed in hydrogen at 1500–1800°C.



The most intensive TL response is shown by crystals doped with Ti and Mo (∼ 10−3wt.%) grown by Czochralski method in reducing conditions. The former may be used to the detection of γ-rays dose ≥ 10−3 − 10−2 Gy, the latter ≥ 10−7 − 10−6 Gy.



Die Thermolumineszenz (TL) von Korund-Einkristallen wird im Hinblick auf die Praparationsmethode und Dotierung beschrieben. Die undotierten Kristalle zeigten eine relative schwache TL bei 15 und 110°C (λ = 330 und 495 nm). Die nach der Verneuil-Methode gezuchteten und im Wasserstoff getemperten Rubin-Kristalle (0,03 Gew.% Cr) zeigten eine erhohte TL bei 275°C (λ = 695 nm). Eine ausgepragte Intensitat der Thermolumineszenz (160°C, λ = 420 nm) zeigten die mit Ti und Mo dotierten (∼ 10−3Gew.%) Kristalle, welche nach der Czochralski-Methode in reduzierender Atmosphare gezuchtet wurden. Der beschriebene Rubin ermoglichtes, die Dosis von γ-Strahlen ≥ 10−3 – 10−2 Gy und beim letztgenannten Material ≥ 10−7 – 10−6 Gy zu messen.

Influence of dopants and preparation method on the thermoluminescence properties of corundum crystals

Spectral properties of YAG and YAP grown in vacuum or under ArH2 protective atmosphere were compared. The latter contained small amounts of argon which was detected by a laser mass spectral analysis. Ar impurity evokes brown colour of unannealed crystals and strenghtens anomalous red colour of annealed (Particularly in O2) YAP crystals doped with Nd + Cr or Nd + Mo. The same red coloration of the doped YAGs is less stable.



Es werden spektrale Eigenschaften der im Vakuum oder unter ArH2 Atmosphare gezuchteten Yttrium-Aluminate verglichen. Die Einkristalle enthalten eine kleine Menge Argon, die man mittels Laser Massen-Spektralanalyse nachweisen kann. Eine braune Farbung der ungetemperten YAG- und YAP-Einkristalle ebenso wie die anomale rote Farbung der mit Nd + Cr oder mit Nd + Mo dotierten und getemperten (besonders in O2) YAP-Einkristalle werden durch die Anwesenheit von Ar erklart. Die letztgenannte rote Farbung der dotierten YAG-Kristalle ist relativ unstabil.

The role of argon in yttrium aluminates

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