Strontium aluminate

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Strontium aluminate
Europium doped strontium silicate-aluminate oxide powder under visible light, long-wave UV light, and in total darkness.
Names
IUPAC name
Strontium aluminate
Identifiers
3D model (
JSmol
)
ECHA InfoCard
 100.031.310 Edit this at Wikidata
EC Number
  • 234-455-3
  • InChI=1S/2Al.5O.2Sr/q2*+3;5*-2;2*+2
  • [O-2].[O-2].[O-2].[O-2].[O-2].[Al+3].[Al+3].[Sr+2].[Sr+2]
Properties
SrAl2O4
Molar mass 205.58 g/mol
Appearance Pale yellow powder
Density 3.559 g/cm3
Structure
Monoclinic
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Strontium aluminate is an

monoclinic crystalline powder that is odourless and non-flammable. When activated with a suitable dopant (e.g. europium, written as Eu:SrAl2O4), it acts as a photoluminescent phosphor with long persistence of phosphorescence
.

Strontium aluminates exist in a variety of other compositions including SrAl4O7 (monoclinic), Sr3Al2O6 (

orthorhombic
). The different compositions cause different colours of light to be emitted.

History

Phosphorescent materials were discovered in the 1700s, and people have been studying them and making improvements over the centuries. The development of strontium aluminate pigments in 1993 was spurred on by the need to find a substitute for glow-in-the-dark materials with high luminance and long phosphorescence, especially those that used promethium. This led to the discovery by Yasumitsu Aoki (Nemoto & Co.) of materials with luminance approximately 10 times greater than zinc sulfide and phosphorescence approximately 10 times longer, and 10 times more expensive. The invention was patented by Nemoto & Co., Ltd. and licensed to other manufacturers and watch brands.[1] Strontium aluminates are now the longest lasting and brightest phosphorescent material commercially available.

For many phosphorescence-based purposes, strontium aluminate is a superior phosphor to its predecessor, copper-activated zinc sulfide, being about 10 times brighter and 10 times longer glowing.[citation needed] It is frequently used in glow in the dark objects, where it replaces the cheaper but less efficient Cu:ZnS that many people recognize with nostalgia – this is what made 'glow in the dark stars' stickers glow.

Advancements in understanding of phosphorescent mechanisms, as well as advancements in molecular imaging, have enabled the development of novel, state-of-the-art strontium aluminates.[2]

Properties

Strontium aluminate phosphors produce green and

crystal field splitting of the 5d orbital energy levels.[3]

diver's watch
to make it readable in low light conditions.
Blue-green (emission at 485 nm) BGW9 Super-LumiNova applied on a similar diver's watch face.

The excitation wavelengths for strontium aluminate range from 200 to 450 nm, and the emission wavelengths range from 420 to 520 nm. The wavelength for its green formulation is 520 nm, its aqua, or blue-green, version emits at 505 nm, and its blue emits at 490 nm. Strontium aluminate can be formulated to phosphoresce at longer (yellow to red) wavelengths as well, though such emission is often dimmer than that of more common phosphorescence at shorter wavelengths.

For europium-dysprosium doped aluminates, the peak emission wavelengths are 520 nm for SrAl2O4, 480 nm for SrAl4O7, and 400 nm for SrAl12O19.[4]

Eu2+,Dy3+:SrAl2O4 is important as a persistently luminescent phosphor for industrial applications. It can be produced by molten salt assisted process at 900 °C.[5]

The most described type is the stoichiometric green-emitting (approx. 530 nm) Eu2+:SrAl2O4. Eu2+,Dy3+,B:SrAl2O4 shows significantly longer afterglow than the europium-only doped material. The Eu2+ dopant shows high afterglow, while Eu3+ has almost none. Polycrystalline Mn:SrAl12O19 is used as a green phosphor for

sol-gel process.[6]

The wavelengths produced depend on the internal

rare-earth halides
) can significantly influence the emission wavelengths.

Strontium aluminate phosphor is usually fired at about 1250 °C, though higher temperatures are possible. Subsequent exposure to temperatures above 1090 °C is likely to cause loss of its phosphorescent properties. At higher firing temperatures, the Sr3Al2O6 undergoes transformation to SrAl2O4.[7]

Cerium and manganese doped strontium aluminate (Ce,Mn:SrAl12O19) shows intense narrowband (22 nm wide) phosphorescence at 515 nm when excited by ultraviolet radiation (253.7 nm mercury emission line, to lesser degree 365 nm). It can be used as a phosphor in fluorescent lamps in photocopiers and other devices. A small amount of silicon substituting the aluminium can increase emission intensity by about 5%; the preferred composition of the phosphor is Ce0.15Mn0.15:SrAl11Si0.75O19.[8]

However, the material has high hardness, causing abrasion to the machinery used in processing it; manufacturers frequently coat the particles with a suitable lubricant when adding them to a plastic. Coating also prevents the phosphor from water degradation over time.

The glow intensity depends on the particle size; generally, the bigger the particles, the better the glow.

Strontium aluminate is insoluble in water and has an approximate pH of 8 (very slightly basic).

Structural material

Strontium aluminate

radiation shielding. The use of strontium aluminate cements is limited by the availability of the raw materials.[9]

Strontium aluminates have been examined as proposed materials for immobilization of

fission products of radioactive waste, namely strontium-90.[10] Europium-doped strontium aluminate nanoparticles are proposed as indicators of stress and cracks in materials, as they emit light when subjected to mechanical stress (mechanoluminescence). They are also useful for fabricating mechano-optical nanodevices. Non-agglomerated particles are needed for this purpose; they are difficult to prepare conventionally but can be made by ultrasonic spray pyrolysis of a mixture of strontium acetylacetonate, aluminium acetylacetonate and europium acetylacetonate in reducing atmosphere (argon with 5% of hydrogen).[11]

Industrial and commercial applications

Reusable and non-toxic glow stick made from strontium aluminate particles mixed with a settable material. The different colours are made from slightly different strontium aluminate formulas.

Strontium aluminate based afterglow pigments are marketed under numerous brand names such as Core Glow, Super-LumiNova[12] and Lumibrite, developed by Seiko.

Many companies additionally sell products that contain a mix of strontium aluminate particles and a 'host material'. Due to the nearly endless ability to recharge, strontium aluminate products cross many industries. Some of the most popular uses are for street lighting, such as the viral bike path.[13]

Companies offer an industrial marble aggregate mixed with the strontium aluminate, to enable ease of using within standard construction processes. The glowing marble aggregates are often pressed into the cement or asphalt during the final stages of construction.

Reusable and non-toxic glow stick alternatives are now being developed using strontium aluminate particles.

Cubic strontium aluminate can be used used as a water-soluble sacrificial layer for the production of free-standing films of complex oxide materials.[14][15]

Safety

Strontium aluminates are considered non-toxic, and are biologically and chemically inert.[16]

Care should be used when handling loose powder, which can cause irritation if inhaled or exposed to mucous membranes.[16]

References

  1. ^ United States Patent 5,424,006 'Phosphorescent phosphor'
  2. ISSN 0272-8842
    .
  3. S2CID 13801803
    .
  4. doi:10.1111/j.1151-2916.1998.tb02349.x
    .
  5. PMID 26447865
    .
  6. doi:10.5755/j01.ms.19.4.2670
    .
  7. doi:10.1021/jp022062c
    .
  8. ^ "Archived copy" (PDF). Archived (PDF) from the original on 2015-12-10. Retrieved 2015-12-08.{{cite web}}: CS1 maint: archived copy as title (link)
  9. ISBN 9780203302118. Archived
    from the original on 2021-06-28. Retrieved 3 March 2016.
  10. ^ "Archived copy" (PDF). Archived (PDF) from the original on 2015-12-08. Retrieved 2015-12-08.{{cite web}}: CS1 maint: archived copy as title (link)
  11. ISBN 9780470588239. Archived
    from the original on 2021-06-28. Retrieved 3 March 2016.
  12. ^ "RC TRITEC Ltd. : Swiss Super-LumiNova". Archived from the original on 5 July 2018. Retrieved 3 March 2016.
  13. ^ Cross, Daniel T. (2019-04-15). "A sun-powered bicycle path glows in the dark in Poland". Sustainability Times. Retrieved 2021-09-30.
  14. S2CID 174809623
    .
  15. PMID 27618712
    .
  16. ^ a b MSDS

External links

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