Triboluminescent materials and devices

Compounds of formula I:

• wherein
• x is 1 or 2
• M is selected from Europium, Terbium, Dysprosium and Samarium;
• R1, R2 and R3 are independently of each other selected from phenyl, naphthyl,
• H and C1-C6 branched or straight chain alkyl, thiophene and C1-C6 fluorinated alkyl wherein the fluorination may be in 1 or all positions or any intermediate value,
• substituted phenyl wherein the substituents are independently selected from C1-C4 straight or branched chain alkyl, Cl, Br, F, I and the phenyl group may be substituted in 1, 2 or 3 positions;
• R4 and R5 are independently of each other selected from phenyl, tolyl, naphthyl, C1-C6 branched or straight chain alkyl and substituted phenyl wherein the substituents are independently selected from C1-C4 straight or branched chain alkyl and the phenyl group may be substituted in 1, 2 or 3 positions;
• R6 is selected from C1-C6 branched or straight chain alkyl and —(CH2)nP(O)R7 R8, wherein n=1 to 4, wherein R7 and R8 are independently selected from phenyl, naphthyl, C1-C6 branched or straight chain alkyl and substituted phenyl wherein the substituents are independently selected from C1-C4 straight or branched chain alkyl and the phenyl group may be substituted in 1, 2 or 3 positions,
• provided that when R4, R5, R7 and R8 are all selected from phenyl then X is 2 or R2 is other than H.